Diagnostic Procedure
WARNING: This page is about a different car, the 1998 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
- DTC U1255 does not necessarily represent an MSM failure. If DTCs are history, check each module on class 2 data line before diagnosing class 2 data line.
- Clear all DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES (DTCS) under SELF-DIAGNOSTICS. Cycle ignition. Check for DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES (DTCS) under SELF-DIAGNOSTICS. If DTC U1255 is current, ensure all modules on class 2 serial data line are functioning properly. Check for short to ground or voltage in circuit No. 1807 (Purple wire) between MSM and other modules on class 2 serial data line. Check for poor connections at MSM. If components, circuit and connections are okay, replace MSM.