P2C21Engine Oil Temperature Sensor A/B Correlation
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- Engines with two oil temperature sensors can check them against each other; P2C21 means sensors A and B disagree although each signal is electrically valid. GM runs up to three tests in its 2019 and 2025 tables (19OBDG03D, 25OBDG03B): after a cold soak (engine off over 540 s or 2,100 s) oil, coolant and intake air must start within 16 °C of each other; the 2025 table also expects the oil to reach 70 °C once enough air has passed; and in operation A and B may differ by no more than 15.8 °C (8 of 10 samples). Type B, MIL after two trips. GM table 23OBDG07 sets it above 15 °C between the two sump sensors, likewise on two trips. A GM patent describes the coolant/intake comparison. Single-sensor faults are P0196 (A) and P01BA (B); typical causes are a drifting sensor or corroded contacts.
- What you may notice
- MIL after two trips
- Oil life or oil temperature display may be wrong
- Usually no change in driveability
- Likely causes
- LikelyOne oil temperature sensor drifting or stuck within its range
- PossibleCorroded or loose contacts adding resistance on one sensor
- RareLow oil level leaving one sensor partly uncovered
- RareBlock or oil heater use skewing the cold-start comparison
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €40 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.