P0603: nonvolatile-memory checks occur at both startup and shutdown

P0603 is commonly labeled a keep-alive-memory error. The cited GM ECM and TCM tables describe invalid nonvolatile memory, including static and preserved memory regions. This is a broader and more precise description than assuming a simple loss of a battery-fed memory circuit.

The event may belong to shutdown

The source lists static-region and preserved-region errors detected during controller initialization. It also lists a preserved-region error detected during shutdown. A fault discovered on the next scan can therefore relate to the preceding power-down process, not necessarily to the moment when the engine was most recently started.

That timing makes the complete power cycle relevant to verification. An immediate check with the controller still awake does not exercise every listed path. Conversely, repeated resets without preserving the original record can obscure when the failure occurred.

Identify the memory owner

Both ECM and TCM sections contain P0603. Confirm the storing module before associating the code with engine or transmission control. The table does not state that battery disconnection is the cause, prescribe a keep-alive fuse test, or authorize replacing either controller automatically.

The useful diagnostic distinction is between an initialization memory-integrity failure and a shutdown preservation failure. Apply the exact module's service procedure and verify through the relevant controlled power-up and power-down sequence. Both documented implementations list a one-trip Type A classification; the generic title alone does not provide a complete repair diagnosis.

Source and applicability

Documented monitors in gm-2025-03a, model year 2025. These are module/calibration examples; vehicle, engine and transmission applicability must be confirmed independently. GM 2025-03a, page 359. GM 2025-03a, page 1081.