P2C21: two sump oil-temperature readings disagree

P2C21 is an oil-temperature correlation code. The selected 25OBDG07A Part 2 row compares oil temperature sensor 1 with sensor 2 in the sump. It fails when the absolute difference exceeds 15°C for the listed 0.1-second duration, subject to the table's basic enable conditions.

Correlation does not identify the inaccurate sensor

The absolute-difference calculation discards direction. Sensor 1 reading too high and sensor 2 reading too low can produce the same magnitude of disagreement. The code therefore identifies a consistency problem without proving which measurement is wrong or that the oil itself is overheated.

A useful diagnostic record preserves both temperatures, their difference and operating history. Agreement with an independent temperature reference is more informative than selecting one sensor merely because it has the less plausible label. Compare the values under conditions appropriate to the service procedure; a generic cold-soak threshold from another calibration should not replace this row's direct comparison.

Keep calibrations separate

Other GM tables associate P2C21 with broader cold-start, warm-up and continuous rationality strategies. Those algorithms must not be blended into a single universal diagnostic. This article uses only the simple two-sensor sump comparison cited below, and the unresolved file-to-application mapping prevents a model claim.

Verification should show both sensor channels remaining mutually consistent while the applicable monitor runs. A dashboard temperature gauge cannot usually demonstrate that two separate monitored inputs agree. The source does not specify sensor access, part replacement or oil-service requirements.

Source and applicability

Documented 2025 GM gm-2025-07a-2 monitor only; vehicle, engine and controller applicability must be established separately. The download-index/application-matrix filename join is unresolved; no model or engine is inferred. GM monitor table, PDF page 611.