P20E4: particulate-filter temperature correlation uses startup references

P20E4 concerns correlation between the exhaust-temperature measurements upstream and downstream of the particulate filter in this GM calibration. It evaluates captured startup values, not an unrestricted comparison of two live readings during regeneration or sustained engine load.

A cold-start comparison with a lookup limit

The table requires at least 28,800 seconds of engine-off time, equivalent to eight hours. The engine must then be running under the specified startup conditions, afterrun must be inactive and the diagnostic must not already have been performed in that driving cycle.

The absolute temperature difference is evaluated against Look-Up Table 32. The summary prints a wide range of possible calibration values rather than one universal allowable difference. Selecting a single number from that range would conceal the lookup dependence and could misclassify an otherwise legitimate reading.

Preserve capture time and sensor identity

Record both captured startup temperatures, the off-time history and the applicable lookup context. Comparing a later downstream value with an earlier upstream value would not reproduce the paired startup observation described by the monitor.

The disagreement does not prove that the particulate filter is damaged or identify which sensor is biased. The source also requires its general enabling and inhibition conditions to be satisfied. Use the matching engine procedure and calibration data to evaluate those details. Physical exhaust work needs the proper heat precautions; this parameter table is not a sensor-removal or filter-replacement instruction.

Source and applicability

GM 2015 15OBDG04 Engine Diagnostics, cited startup particulate-filter temperature correlation monitor only. Individual vehicle, engine, wiring and calibration applicability has not been established from this parameter file.

General Motors source, physical page 196 · General Motors source, physical page 197