What it means
The signals of cylinder head temperature sensors A and B do not correlate within the calibrated tolerance. One sensor drifts or installation offset between the two channels.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Cylinder head temperature sensors A and B provide separate temperature signals to the ECM. This code sets when their readings differ beyond the calibrated tolerance, which can happen if one sensor has drifted or the channels are connected to the wrong harnesses.
Common causes
Most likely first.
- One sensor characteristic drifted
- Harness incorrectly swapped between channels
Symptoms
- Check-engine light
- Engine temperature reading may be inaccurate
- Cooling fan may run unexpectedly
How to diagnose it
- Compare freeze-frame and live readings from sensors A and B when the engine is cold and as it warms to identify which channel diverges.
- Inspect both sensor connectors and harness routing to confirm A and B have not been swapped and that neither connection is loose or corroded.
- Check that both sensors are installed correctly and seated as intended, since a different installation position can create an offset.
- Compare each sensor's resistance or output with the manufacturer's specification at the same conditions.
- If wiring and installation are correct, test each channel independently and replace the sensor that shows drift.
Common fixes
- Reconnect the A and B harnesses to their correctly identified sensors if they were swapped.
- Correct a loose or improperly seated sensor installation.
- Repair corroded or damaged wiring or connector terminals on the affected channel.
- Replace the A or B sensor that fails comparison with the manufacturer's specification.
Can I keep driving?
Unexpected fan operation or inaccurate temperature readings may occur while the ECM sees conflicting sensor data. Monitor the temperature gauge and stop safely if the engine overheats.
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.