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P012F

Engine Coolant Temperature / Engine Oil Temperature Correlation

Engine coolant and oil temperature readings disagree beyond plausible limits. The engine coolant temperature sensor feeds warm-up enrichment, fan control and closed-loop entry — a stuck-cold reading keeps the engine in open loop and rich forever.

  • Check engine light: Yes
  • Emissions related: Yes
  • Repair difficulty: easy

Symptoms

  • Check engine light on
  • Cooling fan runs constantly or not at all
  • Cabin heater weak or excessively hot
  • Possible long warm-up time or hard cold start

Common causes

Ordered by how often each turns out to be the cause.

  • One sensor driftedCommon

Parts involved

  • ECT Sensor
  • Oil Temp Sensor

P012F is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.