Powertrain, generic (extended)

P2C21 Engine Oil Temperature Sensor A/B Correlation

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

One oil temperature sensor drifting or stuck within its range
Corroded or loose contacts adding resistance on one sensor
Low oil level leaving one sensor partly uncovered
Block or oil heater use skewing the cold-start comparison

Symptoms

  • MIL after two trips
  • Oil life or oil temperature display may be wrong
  • Usually no change in driveability

Repair estimate

DifficultyMediumDIY possible
Parts and labour€40–300
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

engine oil temp sensor aengine oil temp sensor becm

Related codes

P0196P01BAP0195P01B9P0197P01BB

References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com, patents.google.com.