What it means
The module detects that engine coolant temperature sensor 1 and sensor 2 readings do not agree within the expected limits.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Engine coolant temperature sensors 1 and 2 provide separate temperature readings that the control module compares to check whether the readings agree. P011A sets when their difference exceeds the expected correlation, which can result from a biased sensor or a fault in either sensor's wiring.
Common causes
Most likely first.
- One coolant temperature sensor drifting or biased
- Faulty sensor wiring or connector
- Poor electrical connection or corrosion
- Less commonly, a module fault
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
How to diagnose it
- Review freeze-frame data and compare ECT sensor 1 and sensor 2 live readings when the engine is cold and again during warm-up.
- Identify both sensors from the vehicle's service information, then inspect each connector and harness for corrosion, looseness, or damage.
- Check coolant level and confirm both sensors are exposed to coolant as intended, since air or low coolant can distort readings.
- Compare each sensor's temperature response with the other and with actual engine warm-up to identify which reading is biased.
- Test the suspect sensor's wiring and output against the manufacturer's specification before considering a control-module fault.
Common fixes
- Repair a loose, corroded, or damaged connector on the affected temperature sensor circuit.
- Repair damaged wiring to the sensor whose reading disagrees.
- Correct low coolant or trapped air that is affecting sensor contact with coolant.
- Replace the biased coolant temperature sensor if its output fails the manufacturer's specification.
Can I keep driving?
A short drive may be possible if the temperature gauge remains normal, but stop if the engine overheats or the fan fails to control temperature. Disagreeing readings can cause incorrect fan or fueling decisions, so diagnose the fault before relying on the vehicle for a long trip.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.