P262B: The control module’s power-off timer fails increment or agreement checks

P262B concerns the controller's hardware timer used while run/crank is inactive in the reviewed GM strategy. It is a timekeeping-performance diagnosis, not simply an indication that the vehicle has been parked for an unusually long period.

Two tests examine different timer behavior

The count-up test checks the interval between consecutive timer readings. A difference greater than 1.50 seconds is abnormal for the documented one-second sampling interval. The decision requires eight failures out of 40 samples.

The range test compares the hardware timer with a mirror timer. Both start when run/crank becomes inactive. A variation above 0.25% is the failure criterion when controller shutdown begins or run/crank becomes active again. The percentage is an agreement limit, not a fixed quarter-second allowance.

Shutdown timing changes what can be observed

The count-up check runs continuously while run/crank is inactive until controller shutdown is initiated. The range comparison happens once per trip at the specified transition. A recording gathered only during ordinary engine operation may therefore miss both of the relevant opportunities.

Preserve power-mode transitions and any available timer diagnostic status when evaluating recurrence. The code identifies incorrect timing behavior, but the summary does not isolate an internal timer component, power interruption or software cause.

Verification should show normal timer incrementing and agreement across an applicable shutdown or wake transition. The source documents Type B, two-trip behavior and does not justify replacing or reprogramming the controller solely from the code.

Source and applicability

These limits describe the stated monitor and require vehicle, hardware and calibration confirmation. GM diagnostic table, PDF page 665.