P050C: Cold-start coolant plausibility uses prior heat history

P050C compares coolant temperature with intake-air temperature at key-on in GM's group 04 strategy. The description extends onto the next PDF page, where additional heat-history and exclusion conditions are given. Reading the first row alone would miss important qualifications.

Both directions of disagreement are considered

The printed comparison includes coolant more than 15°C above intake temperature and, on the continuation page, coolant more than 10°C below it. These are limits for this implementation. They do not identify which sensor is inaccurate, nor do they prove a cooling-system part has failed.

Previous running, accumulated airflow and shutdown temperature affect qualification. The controller also accounts for block-heater use and a heat-history condition associated with strong wind or an open hood. These factors can change how quickly the two sensor locations cool.

Verify the comparison that actually failed

Preserve the key-on temperatures and the prior shutdown conditions. A later warmed-up comparison answers a different question and cannot reconstruct the cold-start evidence. Likewise, an aborted or unqualified test should not be counted as a pass.

Use the vehicle-specific diagnostic procedure to determine whether the temperature inputs are credible under the required history. After correction, confirm a completed qualified cold-start monitor. Clearing P050C or performing repeated warm restarts can leave the original temperature disagreement entirely untested.

Source and applicability

2009 General Motors diagnostic parameter file 09OBDG04 Engine Diagnostics.pdf. Section-specific modules and calibrations; no per-code model or engine applicability established. This explanation describes the documented monitor, not a universal repair procedure.

GM diagnostic parameters, PDF page 23 · GM diagnostic parameters, PDF page 24.