WAMS GM Electronics Glossary

The Audio Control Module (ACM) is the radio in GM HMI-based infotainment systems — separate from the HMI module and separate from the touchscreen. It contains the AM/FM/HD Radio/SiriusXM tuner and either drives the speakers directly (base audio configurations) or hands audio data off over MOST bus to an external amplifier (Bose/premium audio configurations).

On IO5 and IO6 vehicles (2014–2019 era), the ACM is a discrete module that can be replaced or upgraded independently of the HMI. The radio must match the vehicle’s audio configuration:

• Vehicles with RPO codes UQ3, UQ5, UQF (Base audio) use a base ACM.
• Vehicles with UQG (Enhanced Audio with Amplifier) use an ACM matched to the amplifier.
• Vehicles with UQA, UQS, UQH (Premium/Bose) use a Bose-spec ACM that outputs audio data over MOST to the Bose amplifier.

You cannot mix and match Bose and base ACMs — installing a base ACM in a Bose-equipped vehicle (or vice versa) results in no audio. GM also refers to the ACM as the “Silverbox” on some platforms.

On CSM-based vehicles (2017.5+ Cadillac, 2018.5+ other brands), there is no separate ACM — the tuner and audio routing are integrated into the CSM itself.

A failed ACM typically presents as no audio (with the HMI otherwise working), missing HD Radio, missing SiriusXM, or “LOCKED”/”THEFTLOCK” if the VIN authority handshake fails.

Also known as: Radio, Head Unit, Silverbox

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Android Auto is Google’s smartphone-projection platform — the Android counterpart to Apple CarPlay. It lets a compatible Android phone use the vehicle’s infotainment display, microphone, and speakers for Google Maps navigation, music, calls, messages, and Google Assistant.

Android Auto support across GM infotainment generations mirrors CarPlay closely:

• HMI 1.1 / 2.0 (2013–2015) — No native Android Auto support. Can be retrofitted via a WAMS upgrade kit.
• HMI 2.5 (2016–2019) — Wired Android Auto supported natively. No wireless.
• 2016 model year exception — 2016 GM vehicles shipped with native CarPlay support but Android Auto was added via a mid-cycle update. WAMS performs Android Auto activation for 2016 vehicles that didn’t receive the update.
• CSM (2017.5+) — Wired Android Auto supported natively. Wireless Android Auto added on selected later CSM platforms.
• CSM with Google Built-in / IOK — Wired and wireless Android Auto plus native Google services.

WAMS offers wireless Android Auto upgrade kits for many vehicles that originally shipped with wired-only support, often bundled with CarPlay wireless and HD Radio upgrades into a single retrofit.

Also known as: Android Auto, Google Android Auto

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The Body Control Module (BCM) is the central computer that manages a GM vehicle’s body electronics: interior and exterior lighting, power windows and locks, anti-theft authority, chime and warning sounds, key fob recognition, and — critically — the VIN authority that other modules (HMI, CSM, ACM, cluster) authenticate against when the vehicle is started.

When the BCM is replaced, the new module must be programmed to the vehicle’s VIN before other modules will trust it. If the BCM fails to send the proper VIN data over GMLAN to the radio, the radio will display “LOCKED” or “THEFTLOCK” and refuse to operate until the VIN authority is restored.

Many infotainment problems that initially appear to be HMI or radio failures are actually BCM problems. Symptoms of a failing BCM can include:

• Radio displays “LOCKED” or “THEFTLOCK” after a battery disconnect or replacement
• Intermittent failure of windows, locks, or interior lights
• Phantom warning chimes
• Loss of communication between modules on GMLAN
• Key fob recognition failures

WAMS offers VIN-programmed replacement BCMs and custom BCM programming for both Global A and Global B vehicles. Custom programming covers manual transmission conversions, RPO changes, and option enablement on platforms where the dealer cannot perform the work.

Also known as: Body Control Module

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Apple CarPlay is Apple’s smartphone-projection platform that lets a compatible iPhone use the vehicle’s infotainment display, microphone, and speakers for navigation, music, calls, messages, and Siri.

CarPlay support across GM infotainment generations:

• HMI 1.1 / 2.0 (2013–2015) — No native CarPlay support. Can be retrofitted via a WAMS upgrade kit that swaps the HMI 2.0 and matching radio for HMI 2.5 hardware plus a high-speed USB hub.
• HMI 2.5 (2016–2019) — Wired CarPlay and Android Auto supported natively. No wireless support.
• CSM (2017.5+) — Wired CarPlay supported natively. Later CSM versions add wireless CarPlay on selected platforms.
• CSM with Google Built-in / IOK (newer) — Wired and wireless CarPlay supported.

WAMS offers wireless CarPlay/Android Auto upgrade kits for many CSM-based vehicles that originally shipped with wired-only CarPlay, including Cadillac CT4, CT5, XT5, XT6, Blazer, Camaro, and Corvette C7.

Aftermarket “dongle” wireless adapters are generally not recommended — WAMS has seen them cause HMI damage and infotainment instability. The OEM-grade retrofit kits use genuine GM hardware programmed to the vehicle’s VIN.

Also known as: Apple CarPlay, CarPlay

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The Center Stack Module (CSM) is GM’s next-generation infotainment controller, used on 2017.5+ GM vehicles. It debuted on the Cadillac ATS and CTS “.5” refresh in mid-2017.5, expanded to Buick Regal and Buick Encore GX in 2018.5, and rolled out across the broader Chevrolet, GMC, Buick, and Cadillac lineup in subsequent model years. Unlike the older HMI-based architecture (where the HMI, radio/ACM, and amplifier are separate modules connected over MOST bus), the CSM integrates infotainment computing, radio tuning, and most audio processing into a single unified module supplied by Harman.

CSM-equipped vehicles use newer RPO codes rather than the IO4/IO5/IO6 codes used on HMI vehicles:

• IOR — Conventional radio (not actually a CSM, but uses similar home screen styling). No App Shop.
• IOS — CSM with standard CSM features. Most common on non-luxury GM vehicles.
• IOU — CSM with embedded factory navigation.
• IOT — CSM with embedded factory navigation and larger storage.
• IOV — Escalade T1 only; Virtual Cockpit precursor.
• IOK — CSM running Google Built-in (Android Automotive). Found on full-size truck/SUV and 2024–2025 C8 Corvette.
• CPO — Newer CSM variant.

If your vehicle has an App Shop on its home screen, you have a CSM. If you don’t, you have an IOR radio (despite the visually similar UI).

Within the CSM family, GM service literature and resellers commonly identify generations as “HMI / CSM 3.0, 3.5, 3.6, 3.7, 3.8” — this is the unified naming convention used by WAMS as well. It refers to software/hardware revisions of the CSM, not to the original HMI module.

CSM replacement requires VIN programming and, on Global B vehicles, a Techline Connect marriage procedure.

Also known as: Center Stack Module, HMI 3.0, HMI/CSM 3.0, HMI/CSM 3.5, HMI/CSM 3.6, HMI/CSM 3.7, HMI/CSM 3.8, infotainment module 3.x, NGI

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Cadillac User Experience (CUE) is the branded infotainment interface used across the Cadillac lineup. CUE has spanned two distinct hardware generations:

First-generation CUE (2013–2016) uses HMI hardware. The original 2013 Cadillac CUE rollout (ATS, XTS, SRX) used HMI 1.1 with capacitive touch — both for the main 8-inch screen and for the lower climate/audio “haptic” controls below it. Subsequent 2014–2016 CUE vehicles used HMI 2.0 and HMI 2.5.

Second-generation CUE (mid-2017.5 onward) uses CSM hardware. The “CUE” branding continued on Cadillac CSM-equipped vehicles (CT6, XT5, the .5 refresh ATS/CTS) starting in mid-2017.5, but the underlying module is a CSM, not an HMI.

First-generation CUE became known for capacitive-touch failures, the “Ghost Touch” symptom, and “Waiting for Update Media” boot loops. Most of these issues are addressed by replacing the HMI module with a WAMS VIN-programmed replacement, sometimes paired with a new touchscreen assembly.

Identifying which CUE you have:

• Lower capacitive haptic controls + RPO IO4/IO5/IO6 = HMI-based CUE 1.0
• Standard physical buttons + App Shop on home screen + RPO IOS/IOU/IOT = CSM-based CUE

Also known as: CUE, Cadillac User Experience, Cadillac CUE 1.0

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“Ghost Touch” is the common name for a symptom where a GM infotainment touchscreen registers phantom inputs — randomly changing radio stations, opening menus, scrolling lists, or selecting options — as if an invisible finger were operating the screen. It is one of the most frequently misdiagnosed GM infotainment symptoms.

Critical diagnostic point: Ghost Touch is almost always caused by a failing capacitive touchscreen assembly, NOT a failed HMI module. Replacing the HMI on a Ghost Touch vehicle generally does not fix the problem. The fix is a new touchscreen assembly.

Why Ghost Touch happens:

• The capacitive digitizer behind the screen degrades over time
• Internal corrosion or moisture damage causes the digitizer to register inputs that aren’t there
• Connector pin oxidation between the screen and the HMI can introduce false touch coordinates

How to confirm the diagnosis:

• Disconnect the touchscreen from the HMI. If the phantom inputs stop, the screen is the problem.
• If a customer has the patience to swap a screen first before replacing the HMI, they typically save several hundred dollars.

When Ghost Touch IS HMI-related:

• Vehicles where the HMI’s GPU/video subsystem is failing can produce both display artifacts AND apparent ghost inputs simultaneously. In these cases, a full HMI replacement is appropriate. The distinguishing symptom is that the screen shows visible distortion (scrambled pixels, color corruption) alongside the phantom touches.

WAMS sells replacement touchscreen assemblies for HMI-based vehicles where Ghost Touch is the only symptom. For vehicles displaying both Ghost Touch AND distorted graphics, an HMI replacement is the right call.

Also known as: Ghost Touch, Ghost Input, phantom touch, self-operating touchscreen

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Global A is GM’s first-generation electrical and network architecture, predominant on vehicles built from approximately 2010 through 2020. Modules on Global A communicate over GMLAN (a low-speed Single-Wire CAN protocol) and MOST bus (a high-speed multimedia ring), with each major function — HMI, ACM, BCM, instrument cluster, VCIM — living in its own discrete module.

Key Global A characteristics:

• Modular: each function is a separate physical module that can be individually programmed, replaced, or upgraded
• No security gateway: modules can be reprogrammed using GM’s SPS (Service Programming System) without requiring a Techline Connect online marriage
• No native OTA support: software updates require a USB stick at home or a dealer visit
• MOST bus carries multimedia between the HMI, ACM, amplifier, and disc player
• GMLAN carries everything else

Because Global A modules can be programmed without an online dealer connection, most of WAMS’s retrofit and upgrade work happens on Global A vehicles — including HMI replacements, IO5-to-IO6 navigation retrofits, CarPlay/Android Auto upgrades, digital cluster swaps, and BCM custom programming.

The successor to Global A is Global B (Vehicle Intelligence Platform / VIP), which began appearing on Cadillac in 2020 and rolled out across the GM lineup through 2022.

For a complete year-by-year identification guide, see the WAMS Global A vs. Global B Identification Guide.

Also known as: Global A, GM Global A Architecture

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Global B — also known as the Vehicle Intelligence Platform (VIP) — is GM’s second-generation electrical architecture, introduced beginning approximately 2020 and rolled out across the lineup through 2022. Global B replaces Global A and represents a fundamental change in how GM vehicles handle module communication, security, and updates.

Key Global B characteristics:

• High-speed CAN-FD networks (29-bit, up to 5 Mbit/s) replace Global A’s mix of GMLAN and standard CAN
• Centralized gateway module enforces module-level security and authentication
• Native support for over-the-air (OTA) software updates
• Modules must be “married” to the vehicle through GM’s Techline Connect online platform
• Replaces the separate MOST bus with Ethernet-based audio/video transport

Because Global B requires Techline Connect for module marriage, retrofits and replacements on Global B vehicles are more complex than Global A. WAMS coordinates the Techline Connect step as part of every Global B module shipment, either by pre-marrying the module before shipping or by performing the marriage remotely via WAMS2U.

Global B vehicles include Cadillac CT4, CT5, XT4 (2020+), 2021+ Tahoe/Suburban/Yukon/Escalade, 2022.5+ Silverado/Sierra 1500 refresh, Corvette C8, and most 2022+ GM vehicles. GM has announced the Centralized Computing Platform as the successor to Global B, launching first on the 2028 Cadillac Escalade IQ.

For year-by-year identification, see the WAMS Global A vs. Global B Guide.

Also known as: Global B, VIP, Vehicle Intelligence Platform, GM CAN-FD architecture

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GM uses a family of “UQ” RPO codes to identify a vehicle’s factory audio system. The codes split into three tiers:

Base audio (no external amplifier) – UQ3 — Standard base speakers, older GMT900-era code. – UQ5 — Step-up base speakers, no external amplifier. – UQF — Standard Audio. GM’s official definition: “Speaker System Standard Audio.”

Mid-tier enhanced audio (with amplifier, not Bose) – UQG — Enhanced Audio with Amplifier. Has a non-Bose amplifier in the audio path.

Bose premium audio – UQA — Speaker System Premium Audio (Bose) with Amplifier. The most common Bose configuration on GMT900 and K2XX SUVs. – UQS — Speaker System Premium Audio (Bose) with Surround Amplifier. Includes surround sound processing. – UQH — Speaker System Premium Audio Branded (Bose) with Surround Amplifier, Audiophile. Top-tier Bose. Common on Corvette.

Why this matters for module replacement:

When ordering a replacement radio (ACM) from WAMS or anywhere else, you must match the original audio configuration:

• Base audio (UQ3/UQ5/UQF) → requires the base ACM variant
• Enhanced audio (UQG) → requires the matched ACM
• Bose audio (UQA/UQS/UQH) → requires the Bose ACM variant

Installing a base ACM in a Bose-equipped vehicle (or vice versa) results in no audio output. The two ACM variants are not interchangeable.

How to find your audio RPO code:

Locate the SPID label (typically in the glove box) and look for any code beginning with “UQ” — that’s your audio system. On 2018+ vehicles, scan the QR code on the driver’s door B-pillar with a smartphone QR reader.

WAMS lists both base and Bose ACM options on the Replacement GM Radio/ACM Module page; select your audio RPO from the dropdown when ordering.

Note: GM also uses related codes for active noise cancellation (ANC) amplifiers (UQP, UQT, etc.) on newer vehicles. ANC-equipped amplifiers can introduce feedback when paired with aftermarket subwoofers — an ANC bypass harness may be required.

Also known as: Audio RPO Codes, UQ Codes, Bose RPO, Base Audio RPO, UQA, UQG, UQS, UQH, UQ3, UQ5, UQF

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GM uses a set of “UDx” RPO codes to identify which instrument cluster tier is installed in a vehicle. Cluster hardware varies dramatically across these tiers — from a basic monochrome display with analog gauges to a full 12.3-inch digital reconfigurable cluster.

The cluster RPO ladder:

• UDC — Base cluster lens variant. Typically monochrome or limited-graphic driver information display.
• UDD — “Display Instrument-Driver Info Enhanced (Multi Color Standard Graphic).” Mid-tier color driver info display. Standard on most K2XX and T1 truck trims.
• UHS — “Display Instrument-Driver Info Enhanced (Multi Color Enhanced Graphic).” Enhanced color cluster between UDD and UDV.
• UDV — “Display Instrument-Driver Info Enhanced, Full Cluster (Multi Color Graphic).” The top-tier 12.3-inch full digital cluster.

WAMS performs cluster retrofits across these tiers. The most common upgrade path is UDD → UDV — swapping a standard-graphic cluster for the full 12.3-inch digital cluster on platforms where the hardware is compatible. Required work:

• Source the donor 12.3-inch cluster from a same-platform donor vehicle
• Update the cluster’s EEPROM with the recipient vehicle’s VIN and security PIN
• Update the BuildRecord and XMLFile configuration to enable the correct gauges and features
• VIN-program through GM SPS or Techline Connect

WAMS offers complete cluster upgrade services for many platforms — Cadillac CTS to ATS-V cluster, CT4 and CT5 full LCD upgrades, Camaro 6th-gen uplevel cluster, Denali/High Country T1 cluster, Escalade V-style cluster, and many others. See the GM Cluster Upgrade Guide for the full platform-by-platform matrix.

WAMS also sells replacement cluster lenses for specific platforms — useful when the cluster’s protective lens is scratched or damaged but the underlying cluster is still good.

Also known as: Cluster RPO, UDV, UDD, UDC, UHS, GM Cluster Codes, Digital Cluster RPO

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Several frequently-encountered GM option RPO codes determine a vehicle’s telematics and connectivity hardware. These appear on the SPID label alongside the audio (UQx), cluster (UDx), and infotainment (IOx) codes.

UE1 — OnStar Equipped

GM’s official definition: “Communication System-Vehicle, OnStar.” Indicates the vehicle has the full OnStar telematics hardware — VCIM module, cellular antenna, and OnStar service capability. Most GM vehicles from approximately 2000 onward have UE1.

UE0 — OnStar Delete

Indicates the vehicle was specifically built without OnStar hardware. Less common; sometimes appears on export-market vehicles or fleet builds. UE0 vehicles do not have a VCIM module installed. Worth flagging when ordering a CarPlay/Android Auto retrofit because some kits assume OnStar hardware is present.

VV4 — WiFi Hotspot Capability

Indicates the vehicle’s VCIM has the in-vehicle 4G LTE WiFi hotspot capability. Requires an active data subscription (separate from OnStar emergency service). Common on most GM vehicles from approximately 2015 onward.

CWM — Technology Package

Indicates the vehicle was built with GM’s Technology Package option, the specific contents of which vary significantly by vehicle. The Technology Package typically includes the 12.3-inch UDV digital cluster, additional driver-assist features, and often Super Cruise. Where CWM appears varies by model:

• Cadillac CT4, CT5, CT4-V, XT4
• Silverado 1500 2022+ (Global B refresh)
• Sierra 1500 2022+ (Global B refresh)
• Colorado 2023+
• Yukon 2023+
• Bolt EV 2027

The exact features bundled into CWM vary by vehicle — check the vehicle’s full RPO list to determine what’s actually included on a specific build.

Why these codes matter:

For module replacement and retrofit work, knowing whether a vehicle has UE1 vs. UE0 (OnStar present or not) and what’s in CWM (cluster type, driver-assist hardware) is required for correct VIN programming. Send your VIN to WAMS and we’ll pull the complete RPO list before recommending parts.

Also known as: UE1, UE0, VV4, CWM, OnStar Delete, OnStar Equipped, GM Option Codes

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GM has used a sequence of body-on-frame full-size vehicle platforms over the past two decades, each with its own electrical architecture, module compatibility, and retrofit options.

GMT900 (2007–2014 trucks, 2007–2014 SUVs)

The predecessor to K2XX. Used on Silverado, Sierra (light-duty and HD), Tahoe, Suburban, Yukon, Yukon XL, and Escalade. Older Global A electrical architecture. Most GMT900 vehicles do not have HMI infotainment — they use legacy radio head units.

K2 / K2XX (2014–2019 light-duty trucks, 2015–2020 SUVs)

The successor to GMT900. The “K2XX” assembly code refers to the platform family. Used on:

• Silverado 1500 light-duty: 2014–2018 (with some 2019 overlap to T1)
• Sierra 1500 light-duty: 2014–2018 (with some 2019 overlap to T1)
• Silverado/Sierra HD: 2015–2019
• Tahoe, Suburban, Yukon, Yukon XL, Escalade, Escalade ESV: 2015–2020

K2XX trucks and SUVs use Global A electrical architecture, HMI-based infotainment (IO4/IO5/IO6), and the MOST bus. This is the platform where most WAMS retrofit work happens — HMI replacements, IO5→IO6 navigation retrofits, CarPlay/Android Auto upgrades, digital cluster swaps (UDD→UDV), and BCM custom programming.

T1 / T1XX (2019+ light-duty trucks, 2021+ SUVs)

The successor to K2XX. The “T1” assembly code identifies the platform. Used on:

• Silverado 1500 light-duty: 2019+ (pre-refresh on Global A; 2022.5+ refresh on Global B)
• Sierra 1500 light-duty: 2019+ (pre-refresh on Global A; 2022.5+ refresh on Global B)
• Tahoe, Suburban, Yukon, Yukon XL, Escalade, Escalade ESV: 2021+

Pre-refresh T1 trucks (2019–2022 model year) are on Global A with CSM-based infotainment. The 2022.5+ refresh moves to Global B architecture. T1 SUVs (2021+) are on Global B from launch. WAMS performs cluster upgrades (UDD→UDV), CarPlay/Android Auto retrofits, and BCM programming on T1 vehicles.

Alpha (Cadillac compact RWD)

GM’s compact rear-wheel-drive platform — not a truck/SUV platform but worth noting for cluster compatibility and module work. Used on Cadillac ATS, CTS (3rd gen), CT4, CT5, and the 6th-gen Chevrolet Camaro. Spans both Global A (older Alpha) and Global B (Cadillac CT4/CT5).

C7 and C8 (Corvette)

Outside the truck/SUV platforms but worth mentioning. C7 Corvette (2014–2019) uses HMI-based infotainment on Global A. C8 Corvette (2020+) uses CSM-based infotainment on Global B. WAMS performs CarPlay/Android Auto retrofits on C7 and various module work on both generations.

Why platform matters for module work:

The platform determines which electrical architecture is in use, which means which modules are compatible, which programming tools are required, and which retrofit paths are possible. An HMI from a K2XX truck will not work in a T1 truck. A T1 SUV cluster will not work in a K2XX SUV. Always identify the platform before ordering parts.

Also known as: K2, K2XX, T1, T1XX, GMT900, Alpha, GM Truck Platform, GM SUV Platform

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The HMI (Human Machine Interface) module is the primary infotainment controller used on most 2013–2020 GM vehicles equipped with MyLink, IntelliLink, or first-generation CUE. It is the computer — separate from the touchscreen, separate from the radio (ACM), and separate from the speakers — that boots the infotainment operating system and drives everything visible on the center display.

The HMI handles touchscreen input, Apple CarPlay and Android Auto (on HMI 2.5+), factory navigation (on IO6 configurations), Bluetooth pairing, voice recognition, backup-camera rendering, and communication with the radio, instrument cluster, amplifier, and media disc player over GM’s MOST bus.

HMI generations:

• HMI 1.0 — Pre-production engineering hardware. Never shipped to customers.
• HMI 1.1 — 2013 Cadillac CUE only (ATS, XTS, SRX). Rare. Capacitive touch.
• HMI 2.0 — 2014–2015 across the GM lineup. Dual-core processor, 8 GB eMMC. No CarPlay or Android Auto.
• HMI 2.5 — 2016 through approximately 2019/2020. Quad-core processor, 16 GB eMMC. Adds wired CarPlay and Android Auto.

The architectural successor to the HMI is the CSM (Center Stack Module), used on 2019+ refreshed GM platforms. Some GM service literature and resellers refer to the CSM under a unified “HMI / CSM 3.0, 3.5, 3.6, 3.7, 3.8” naming convention. Physically and architecturally, however, the HMI and CSM are distinct modules — different connectors, different chassis, and different supplier (Bosch HMI vs Harman CSM). They are not interchangeable.

For the complete technical breakdown, see the WAMS HMI Guide.

Also known as: Human Machine Interface, infotainment module, infotainment head unit, infotainment computer

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IntelliLink is the branded infotainment interface on GMC and Buick HMI-based vehicles. Like MyLink (Chevrolet) and first-generation CUE (Cadillac), IntelliLink is the user-facing software layer that runs on top of the same underlying HMI module hardware. The only meaningful differences between IntelliLink, MyLink, and CUE are the home screen styling, brand logos at boot, and a few brand-specific menu items.

IntelliLink generations match HMI generations:

• IntelliLink 1.x — Earliest deployment, 2012–2013.
• IntelliLink 2.0 — 2014–2015. No CarPlay or Android Auto.
• IntelliLink 2.5 — 2016–2019. Adds wired CarPlay and Android Auto.

Vehicles displaying “IntelliLink” branding use HMI hardware with IO4, IO5, or IO6 RPO codes. Newer GMC and Buick vehicles use CSM hardware with IOS/IOU/IOT/IOK RPO codes — those don’t carry the “IntelliLink” badge.

IntelliLink shares all the same failure modes as MyLink and HMI-based CUE because they use the same underlying module. Replacement involves a VIN-programmed HMI; WAMS units ship pre-programmed and plug-and-play.

Also known as: IntelliLink, GMC IntelliLink, Buick IntelliLink

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IO4 is the GM Regular Production Option (RPO) code for the base 4.2-inch color display infotainment configuration. It is the entry-level radio package on K2-era trucks and SUVs (2014–2016) — a smaller color display in the center stack, paired with physical buttons and a separate ACM radio module. IO4 does not have the 8-inch touchscreen used on IO5 and IO6 vehicles.

What IO4 includes:

• 4.2-inch color driver information display in the center stack
• AM/FM/SiriusXM radio with physical preset and tuning buttons
• Bluetooth hands-free calling and audio streaming
• USB and AUX inputs
• Basic vehicle settings display

What IO4 does NOT include:

• 8-inch touchscreen (that’s IO5/IO6)
• Apple CarPlay or Android Auto (added on HMI 2.5 with the 8-inch screen)
• Embedded factory navigation (that’s IO6)
• App Shop (that’s CSM)

The most common upgrade for IO4 vehicles is the 4-inch to 8-inch screen upgrade, which converts the vehicle from IO4 to IO5 or IO6 — adding the 8-inch touchscreen, the HMI module, and full MyLink/IntelliLink functionality including CarPlay/Android Auto (on 2016 vehicles). The upgrade requires HMI, screen, harness, and bezel components plus VIN programming to enable the new RPO content.

IO4 vehicles are typically the base or fleet trim levels: 2014–2016 Silverado/Sierra WT or LS, base 2015–2016 Tahoe/Suburban/Yukon, base 2015–2016 Yukon XL, and similar entry trims. The configuration was discontinued as HMI 2.5 standardized on the 8-inch screen across the lineup from 2017 onward.

Also known as: IO4, RPO IO4, base radio, 4.2 inch display, 4-inch screen

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IO5 is the GM Regular Production Option (RPO) code for the non-navigation HMI infotainment configuration: 8-inch touchscreen with MyLink, IntelliLink, or first-generation CUE, but without factory embedded navigation. The vehicle still has full infotainment functionality (Bluetooth, audio sources, backup camera, on HMI 2.5+ wired Apple CarPlay and Android Auto) — it just doesn’t have GM’s built-in map database.

IO5 is the most common infotainment configuration on 2014–2019 GM full-size trucks and SUVs (Silverado, Sierra, Tahoe, Suburban, Yukon, Escalade) and many midsize vehicles. It is paired with the HMI module and the separate radio/ACM module.

Common upgrade paths from IO5:

• IO5 → IO6 navigation retrofit — replaces the HMI with a navigation-equipped variant programmed to the vehicle’s VIN. Adds embedded factory maps and turn-by-turn guidance.
• 2.0 → 2.5 CarPlay/Android Auto upgrade — for 2013–2015 IO5 vehicles, swaps the HMI 2.0 + matching radio + USB hub for HMI 2.5 hardware that supports wired CarPlay/Android Auto.

You can confirm whether your vehicle has IO5 by locating the SPID (Service Parts Identification) label, typically in the glove box, and looking for the “IO5” code. IO5 vehicles will not have the App Shop home screen used by CSM-based infotainment.

Also known as: IO5, RPO IO5, non-nav infotainment

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IO6 is the GM RPO code for the HMI infotainment configuration with embedded factory navigation. The hardware is the same 8-inch touchscreen as IO5 — what’s different is the HMI is a navigation-equipped variant with the GM map database installed, and the SPID label calls out IO6 instead of IO5.

IO6 includes everything IO5 has (Bluetooth, audio sources, backup camera, on HMI 2.5+ Apple CarPlay and Android Auto) plus:

• Built-in GM map database with turn-by-turn directions
• Voice destination entry
• Points-of-interest search without needing a phone

GM has discontinued map database updates for HMI-based IO6 systems; the final map release was in 2023. Vehicles with IO6 can still order the final available map update from WAMS.

An IO5 vehicle can typically be upgraded to IO6 by replacing the HMI with a navigation-equipped unit programmed to the vehicle’s VIN. This is one of WAMS’s standard retrofit services.

Also known as: IO6, RPO IO6, factory nav, HMI navigation

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MOST (Media Oriented Systems Transport) is the high-speed multimedia network protocol used to connect infotainment modules on GM HMI-based vehicles. On a GM vehicle, the MOST bus connects the HMI, the radio (ACM), the amplifier (on Bose/premium audio), the media disc player, and other multimedia modules in a closed ring topology where each module both receives data from the previous module and forwards data to the next.

GM’s MOST implementation uses copper conductors (electrical signaling). The bus is designed to carry the high bandwidth needed for digital audio routing — particularly between the radio and the external Bose amplifier on premium audio configurations.

A break, short, or open anywhere in the MOST ring takes down the entire infotainment system. Because the ring is sequential, a single bad module or bad connector can make every other module on the bus appear to have failed. Common failure presentations:

• All infotainment dead, even though the HMI itself is healthy
• Missing audio with HMI screen still working (often a MOST issue, not an ACM issue)
• Intermittent infotainment that comes and goes with vibration
• “Audio system error” or similar messages

MOST faults are a frequent root cause of symptoms that look like a failed HMI but aren’t. WAMS requires a GM dealer diagnosis before shipping a replacement HMI specifically because a MOST bus open/short can present identically to module failure — and replacing the HMI will not fix a wiring problem.

On Global B vehicles, GM moved away from MOST in favor of Ethernet-based audio/video transport on the CSM. MOST bus is therefore an HMI-era concept.

Also known as: MOST, MOST Bus, Media Oriented Systems Transport, infotainment ring

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MyLink is Chevrolet’s branded infotainment interface. It is the user-facing software layer — the home screen styling, the menu animations, the Chevy logo on boot — that runs on top of the underlying HMI module hardware. Mechanically, the same HMI hardware runs IntelliLink on GMC and Buick vehicles and first-generation CUE on Cadillac vehicles.

MyLink generations correspond directly to HMI generations:

• MyLink 1.x — Earliest HMI-based Chevrolet rollout, 2012–2013.
• MyLink 2.0 — 2014–2015. No CarPlay or Android Auto.
• MyLink 2.5 — 2016–2019. Adds wired CarPlay and Android Auto.

Vehicles displaying the “MyLink” brand at startup are HMI-based and use IO4, IO5, or IO6 RPO codes. Vehicles displaying newer Chevrolet “Infotainment 3” branding are CSM-based and use IOR, IOS, IOU, IOT, or IOK RPO codes.

MyLink failures share the same root causes and symptoms as any HMI failure: “Waiting for Update Media,” black screen, boot looping, and missing CarPlay. The fix is the same — a VIN-programmed replacement HMI.

Also known as: MyLink, Chevy MyLink, Chevrolet MyLink Infotainment

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“Plug and Play” is the term WAMS uses for replacement modules that ship pre-programmed and ready to install without any further programming, dealer visit, scan tool, or Techline session by the customer. The customer removes the old module, installs the WAMS replacement, reconnects the connectors, and the vehicle functions as if the module had been installed at the factory.

What “Plug and Play” means at WAMS:

• The module ships as factory-new OEM GM hardware in original GM packaging — not refurbished, not salvage
• It is VIN-programmed before shipping with the correct software, RPO configuration, and feature set for the customer’s specific vehicle
• It is bench-tested at WAMS after programming, before it leaves
• It requires no dealer Techline session for installation
• It carries the full GM parts warranty on the module itself

For Global A vehicles, Plug and Play is straightforward — the module ships fully programmed and the customer installs it directly. For Global B vehicles where GM’s Techline Connect requires the module to physically be in the vehicle for the marriage step, WAMS coordinates a WAMS2U remote programming session to complete the marriage after install. This preserves the no-dealer-visit benefit.

What “Plug and Play” does not mean:

• It does not mean a module from a third party with no programming
• It does not mean a generic universal replacement
• It does not mean a module pulled from another vehicle and resold

Aftermarket and salvage-yard modules sold as “plug and play” by other sellers frequently arrive Theft-Locked, with wrong feature configurations, or with no programming at all. WAMS Plug and Play means the module behaves as if the factory installed it.

Also known as: Plug and Play, Plug-and-Play, Pre-Programmed

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RPO (Regular Production Option) is the GM standard coding system for vehicle configuration. Every factory-installed option, package, engine, transmission, color, interior, audio system, infotainment configuration, and feature on a GM vehicle is assigned a three-character alphanumeric code. The complete list of RPO codes for a specific vehicle is printed on its SPID (Service Parts Identification) label.

Why RPO codes matter for module work:

• Infotainment compatibility — A replacement HMI must match the original IO4/IO5/IO6 RPO code and the audio configuration (UQ3/UQ5/UQF/UQG/UQA/UQS/UQH).
• Cluster compatibility — A digital cluster replacement must match UDV/UDD/UDC and platform-specific options.
• VIN programming — When WAMS programs a module, the RPO list is the authoritative source for which features, languages, and calibrations to enable.

RPO codes can change meaning across model years and across vehicle families. A G80 RPO is a limited-slip differential on a passenger car but a locking differential on a truck. The same code in 2010 may not mean the same thing in 2025. Always cross-reference RPO codes against the specific vehicle’s model year and platform.

Where to find your RPO list:

• 2018 and newer: Scan the QR code on the driver’s door B-pillar or in the glove box with a smartphone QR reader app.
• 2017 and older: Read the printed RPO sticker on the SPID label, typically in the glove box, trunk floor, or inside the driver’s door panel.

Send your VIN to WAMS and we’ll pull your complete RPO list as part of any module quote.

Also known as: RPO, RPO Code, Regular Production Option, Option Code

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The SPID (Service Parts Identification) label is the physical sticker on a GM vehicle that lists every RPO option code installed at the factory. It is the authoritative source for determining a vehicle’s exact build configuration — what infotainment hardware it has, what audio system, what cluster, what packages, what colors, what engine, and what transmission.

Where to find the SPID label:

• Trucks — Typically inside the glove box.
• SUVs and crossovers — Glove box or spare tire cover in the cargo area.
• Sedans and coupes — Spare tire cover in the trunk floor, or sometimes the inside of the driver’s door panel.
• 2018 and newer — In addition to the printed SPID label, all GM vehicles include a QR code on the driver’s door B-pillar that encodes the VIN and full RPO list. Scanning this with a smartphone QR app is the fastest way to retrieve the data.

What the SPID label contains:

• The vehicle’s VIN
• A complete list of three-character RPO codes
• Color and trim codes (typically prefixed)
• Often: assembly plant code and build date

For WAMS module work, the SPID label or the door QR code is required to ensure the replacement part is configured correctly. A wrong RPO match results in a module that physically fits but produces wrong behavior — wrong audio routing, missing features, or “LOCKED” radio.

Also known as: SPID label, Service Parts Identification, RPO sticker, RPO label

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Theft Lock (often displayed as “LOCKED” or “THEFTLOCK”) is the anti-theft mode that GM radios and other VIN-paired modules enter when their stored VIN doesn’t match the vehicle they are installed in. When triggered, the radio refuses to play audio, accept inputs, or function in any meaningful way until the VIN authority is re-established.

What triggers Theft Lock:

• Installing a used radio or module from a different vehicle
• Replacing the BCM (which holds VIN authority) without proper programming
• Battery disconnect or voltage spike that disrupts the VIN handshake on the GMLAN bus
• A failing BCM that stops sending VIN data correctly

GM’s Theft Lock system is designed to prevent stolen modules from working in other vehicles — and it works exactly as intended. A salvage-yard radio installed in a different VIN will display Theft Lock on first power-up and never recover without the correct programming.

How to clear Theft Lock:

• Replacement module from WAMS — Ships VIN-programmed to your specific vehicle. No Theft Lock on install.
• Module pulled from another vehicle — Requires a “regreen” / VIN clear service. WAMS performs this for HMI modules via the HMI Theft Lock Removal ship-in service.
• BCM-related Theft Lock — Often resolved by diagnosing and replacing the underlying BCM issue rather than the radio.

If your radio displays Theft Lock after a battery disconnect on a vehicle where nothing was swapped, the BCM is the most likely culprit — not the radio.

Also known as: Theft Lock, THEFTLOCK, LOCKED, VIN Lock

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UDV is the GM Regular Production Option (RPO) code for the 12.3-inch full-color reconfigurable digital instrument cluster. In GM’s official terminology, UDV stands for “Display Instrument-Driver Info Enhanced, Full Cluster (Multi-Color Graphic).”

UDV clusters replace the traditional analog gauges entirely with a single large LCD that can render multiple gauge styles, navigation maps, vehicle status pages, and driver-assist visualizations. The cluster is a full electronic control module — not just a display — and is VIN-programmed to integrate with the rest of the vehicle’s electrical architecture.

UDV is one of three related cluster RPOs:

• UDC — Base cluster lens variant (typically monochrome or limited-graphic).
• UDD — Mid-tier “Driver Info Enhanced (Multi Color Standard Graphic)” cluster. Common on K2XX-era trucks.
• UHS — Enhanced graphic cluster between UDD and UDV.
• UDV — Top-tier 12.3-inch full digital cluster.

UDV clusters appear on premium Cadillac trims (CTS-V, CT6, Escalade), select Chevrolet/GMC top-trim vehicles (Denali, High Country), and on Corvette C8.

WAMS performs UDV retrofits — installing a 12.3-inch digital cluster on vehicles that originally shipped with a smaller UDD or UDC variant — including the necessary VIN programming, configuration flags, and EEPROM work to make the cluster behave correctly in the recipient vehicle. See the GM Cluster Upgrade Guide for compatibility and pricing.

Also known as: UDV, RPO UDV, 12.3 cluster, full digital cluster

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The Vehicle Communications Interface Module (VCIM) is the OnStar telematics module in GM vehicles. It contains the cellular modem, GPS receiver, and Bluetooth radio that connect the vehicle to OnStar’s service network and to paired phones. The VCIM is identified by RPO UE1 (OnStar equipped) on the SPID label.

The VCIM handles:

• The OnStar Blue Button service connection
• Automatic crash response and stolen vehicle assistance
• Hands-free Bluetooth calling on vehicles where the VCIM (not the HMI/CSM) owns Bluetooth
• The in-vehicle WiFi hotspot
• GPS for OnStar’s turn-by-turn navigation feature

VCIMs are VIN-locked to the vehicle they shipped with. A used VCIM pulled from another vehicle cannot simply be installed — it must be “regreened” (cleared of the original VIN) and reprogrammed before OnStar will activate it on a new vehicle.

GM vehicles built between approximately 2007 and 2014 used VCIMs that depended on 2G and 3G cellular networks. Those networks were shut down in 2022, leaving those VCIMs unable to connect regardless of their physical condition. For these older vehicles, the OnStar service itself is no longer available — but the VCIM can still be reworked for Bluetooth integration.

WAMS offers a VCIM rework service that adds modern Bluetooth paired-phone functionality to legacy VCIMs and re-greens VCIMs pulled from donor vehicles. The service requires you to ship the VCIM to WAMS.

Also known as: OnStar Module, Telematics Module, Communications Interface Module (CIM)

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VIN Programming is the process of configuring a GM electronic module — an HMI, CSM, ACM, BCM, cluster, VCIM, or other module — to operate as if it had been installed in a specific vehicle at the factory. The module receives:

• The vehicle’s VIN
• The vehicle’s RPO option list (so it enables the correct features, languages, and calibrations)
• The latest applicable software/firmware for that VIN
• Any required security or anti-theft handshakes

A module without VIN programming is a “blank” module — it will physically fit, but the vehicle will reject it with “LOCKED,” “THEFTLOCK,” or “NO VIN” messages, refuse to enable features, or fail to communicate with other modules on the bus.

VIN programming is performed using GM’s official tools:

• SPS (Service Programming System) — the legacy programming environment used on Global A vehicles. Can run via a J2534 pass-through device.
• Techline Connect — GM’s modern online programming platform required for all Global B vehicles and for some advanced Global A work. Requires a paid subscription and an online connection to GM’s servers.

WAMS performs VIN programming on every module we ship, before it arrives at the customer. This is what makes WAMS replacement modules “plug-and-play” — there is no required dealer visit, no Techline session for the customer to schedule, no scan tool required for installation. For Global B modules where Techline Connect requires the module to be physically in the vehicle, WAMS coordinates a WAMS2U remote programming session.

Without proper VIN programming, salvage-yard modules and used modules from other vehicles cannot function correctly — they remain locked to the original VIN until cleared and reprogrammed.

Also known as: VIN Programming, VIN coding, module programming, SPS programming, VIN-matched programming

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“Waiting for Update Media” is the on-screen message that appears when a GM HMI module’s internal eMMC flash storage has corrupted to the point that the infotainment operating system can no longer boot. The HMI is stuck in a recovery state looking for an external USB drive with a valid software image to recover from — software the average customer doesn’t have access to.

This symptom is the single most diagnostic HMI failure indicator. Based on the tens of thousands of replacement units WAMS has shipped, “Waiting for Update Media” is 100% diagnostic for HMI failure. A replacement HMI fixes it every time.

Why it happens:

• HMI modules use eMMC flash storage with finite write endurance
• As vehicles cross the 6–10 year mark, that flash starts to fail
• Once corruption hits the OS partition, the HMI cannot complete its boot sequence
• The recovery message (“Waiting for Update Media”) is the only thing the bootloader can still display

What it looks like:

• The infotainment system boots partially (logo appears) then stops
• A screen reading “Waiting for Update Media” remains indefinitely
• Audio may continue to function (radio plays from the ACM) but no infotainment UI is available
• The screen does not respond to touch

The fix:

A VIN-programmed replacement HMI from WAMS restores normal operation immediately. Installation takes 20–40 minutes at home with a T15 Torx driver and a trim tool. WAMS HMIs ship with the latest available software and map updates (where applicable) pre-loaded.

Vehicles affected most commonly: 2013–2019 GM HMI-equipped trucks, SUVs, and Cadillac CUE vehicles that have crossed the 6–10 year mark.

Also known as: Waiting for Update Media, WFUM, HMI no boot, HMI stuck on update media

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WAMS2U is the WAMS remote programming service. Instead of shipping a module to WAMS for programming, the customer keeps the module in their vehicle and WAMS performs the programming remotely via a scheduled session.

How WAMS2U works:

• The customer schedules a session via the WAMS Contact page with order number reference
• WAMS sends a software download link and a session token
• At the scheduled time, the customer connects a genuine GM MDI1 or MDI2 scan tool (MDI2 required for Global B) to the vehicle’s diagnostic port, then to a Windows 10/11 laptop with a hardwired ethernet connection (Wi-Fi works but is less reliable; cellular hotspots do not work)
• For Global A vehicles, the customer turns ignition to RUN. For Global B vehicles, ignition stays OFF.
• WAMS performs the programming through the customer’s MDI and laptop while communicating via in-software chat
• Programming standard hours are 9 AM – 5 PM Eastern; after-hours available for an additional fee

What WAMS2U is for:

• Global B module marriages that cannot be completed without the module being physically in the vehicle (Techline Connect requirement)
• Custom programming changes that don’t require the module to be removed
• Feature unlocks and option enablement on installed modules
• Situations where shipping a module isn’t practical (fleet vehicles, immobile vehicles)

Required equipment:

• Genuine GM MDI1 (Global A only) or MDI2 (Global A or Global B)
• Windows 10/11 PC with at least 8 GB memory and a working USB-A port
• Hardwired ethernet connection or strong Wi-Fi
• Vehicle battery fully charged, ideally on a charger/tender during the session

WAMS2U is available on services that explicitly offer it as a delivery method, and on certain services that are only available remotely.

Also known as: WAMS2U, WAMS to You, Remote Programming

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