Cooling

P011A — Engine Coolant Temperature Sensor 1/2 Correlation

Severity: medium Drive with care, to a shop

What P011A means

The engine control module compares the signals from two engine coolant temperature (ECT) sensors. Under the same conditions, especially on a fully cold engine, the two readings should be close. When the difference exceeds the allowed limit, the module sets P011A because it cannot tell which sensor is correct.

Symptoms

  • Check Engine Light is on
  • Erratic temperature gauge reading
  • Rough idle, especially on a cold start
  • Higher fuel consumption
  • Reduced power or sluggish acceleration
  • Cooling fan running at the wrong times

Possible causes

  1. Faulty ECT sensor (either one)
  2. Poor connection, corrosion or damaged wiring at the sensor circuits
  3. Low coolant level or air trapped in the cooling system
  4. Thermostat stuck open or closed
  5. Faulty PCM or software issue (uncommon)

How to diagnose

  1. Scan for all codes and review freeze frame data for other cooling-related faults
  2. Check coolant level and condition on a cold engine and look for leaks
  3. Compare both sensor readings with a scan tool on a fully cold engine; they should nearly match
  4. Watch both readings during warm-up and compare with actual temperature from an infrared thermometer
  5. Inspect sensor connectors and wiring for corrosion, chafing and coolant contamination
  6. Measure sensor resistance and compare it to the spec for your vehicle
  7. Check reference voltage and ground at the sensor connectors
  8. Test the thermostat and confirm the upper and lower radiator hoses heat up properly

Common fixes

  • Replace the faulty ECT sensor
  • Repair the wiring or replace the damaged connector
  • Top off coolant and bleed air from the cooling system
  • Replace a faulty thermostat
  • Reflash or replace the PCM only after it is confirmed faulty

Questions and answers

Can I drive with a P011A code?

For a short time, if the engine is not overheating. Still, wrong temperature data hurts engine operation, so get it diagnosed soon.

What most often causes P011A?

Most often it is a failed temperature sensor or a poor connection at its connector. Check coolant level and wiring first, then replace the sensor.

Can I just clear the code?

Clearing it only turns the light off temporarily. If the cause remains, the code will return and the engine keeps running on unreliable temperature data.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.