P246F: Exhaust sensor 4 fails to warm plausibly after a soak

P246F is a bank 1 exhaust-gas temperature sensor 4 plausibility check in the GM 04A monitor. After a qualifying engine-off soak, the controller compares a later maximum temperature with a reference captured around key-on. It tests whether the temperature behaviour makes sense, rather than only whether the signal lies between electrical range limits.

A response check with a temperature-dependent map

The failure criterion is a temperature difference smaller than the applicable calibrated map value. The map depends on the frozen reference temperature; the summary does not provide one fixed number that works at every starting temperature. The source describes this check as capable of identifying a sensor out of the exhaust stream or information that remains stuck, without declaring either the sole cause.

A valid engine-off timer and sufficient soak are required. Communication, high/low range, quick-change and key-on faults are among the conditions that prevent this check. The sensor must also complete its initialization delay.

What distinguishes this diagnosis

A believable temperature at one instant can still fail a response test after warm-up. Retain the initial reference, subsequent temperature behaviour and soak/initialization status where available. Conversely, a sensor already rejected by an electrical diagnostic should not be evaluated as if this plausibility monitor necessarily completed.

The source lists no additional debounce once its conditions are satisfied, but that does not remove the prerequisite soak and response observation. Use the matching service procedure for sensor location and exhaust-system access. The code supports investigating inadequate measured response; it is not an automatic replacement instruction.

Source and applicability

2025 GM 04A documented monitor only; module and calibration applicability must be matched to the vehicle. GM PDF, page 1197. GM PDF, page 1198.