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.