P200C: two downstream DPF overtemperature thresholds

P200C is a diesel particulate filter overtemperature code in the reviewed GM system. The monitored location is downstream of the DPF. The table explicitly describes a safety-related response to excessive sensed temperature, rather than a generic efficiency or pressure-loading test.

Higher temperature receives faster qualification

The first branch requires temperature above 800°C with 300 failing samples out of 450. The second uses temperature above 900°C with 50 failing samples out of 70. Both branches run at 100-millisecond intervals.

This means the monitor does not use one temperature limit with one fixed delay. The hotter branch can qualify with much less accumulated exposure. A brief peak and a longer period above the lower threshold must be evaluated against their respective sample windows.

Trustworthy temperature is a prerequisite

The engine must be running, battery voltage must be in range and the test must be enabled by calibration. The source also requires no downstream DPF temperature-sensor fault. If that sensor has a separate fault, absence of a new overtemperature code is not strong evidence that exhaust temperature is acceptable.

Verification should review the downstream temperature trace, sensor validity and completion of the relevant branch. The row lists Type A, one-trip reporting. It does not identify why temperature rose, guarantee that the filter escaped damage or authorize a regeneration procedure. Because the monitored event involves substantial exhaust heat, inspection and functional testing need the applicable professional service procedure. Exact vehicle and engine applicability remain outside this monitor summary.

Source: GM monitor, PDF page 1383.