P0A01: A cold-soak comparison tests electronics-coolant temperature plausibility

P0A01 checks whether the power-electronics coolant temperature is believable after a long engine-off period. The cited GM cold-start strategy compares that reading with engine coolant and intake-air temperatures. It does not simply ask whether the electronics coolant is hot.

The reference temperatures must agree first

The example requires engine-off time greater than 28,800 seconds, or eight hours. Failure then uses electronics-coolant versus engine-coolant disagreement above 30°C while engine coolant and intake air differ by no more than 15.75°C. The agreement of the other two measurements gives context to the outlying reading.

The pass relationship is different: electronics coolant must be within 15.75°C of both engine coolant and intake air. A reading between the failure and pass boundaries is therefore not automatically proof of a completed passing test.

Preserve the actual cold-start evidence

Record the three startup temperatures and the verified engine-off interval. Measurements taken after warmup cannot recreate the original thermal comparison. The row also excludes several intake-air, engine-coolant, airflow and electronics-coolant circuit faults, so companion codes matter to eligibility.

The page describes a plausibility monitor, not a coolant-fill instruction or proof of a failed sensor. Temperature disagreement must be investigated with the matching cooling-system and sensor information. Access around hybrid power electronics requires the appropriate professional isolation procedure, and an apparently ordinary coolant task should not bypass those requirements.

Source and applicability

GM 2010 10OBDG10 Hybrid Diagnostics, only the cited controller and monitor. These are historical calibration examples; individual vehicle, engine and hardware applicability is not established. GM PDF, page 91.