P011B
Engine Coolant Temperature/Intake Air Temperature Correlation
ECT and IAT readings disagree at long soak (engine off for hours) when both should match ambient. The intake air temperature sensor feeds the ECM's density calculation — a drifted reading miscalculates fuel mass and pushes mixture lean (cold reading) or rich (hot reading).
- 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
- IAT Sensor
P011B 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.