What it means
The module monitors the control circuit for engine coolant heater A and sets this code when its operation falls outside the expected performance range. The code identifies a circuit performance problem, but does not specify the failed part.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Engine coolant heater A warms engine coolant when commanded, and the control module monitors whether the heater circuit responds as expected. This code sets when heater A's circuit operation falls outside its expected performance, without identifying whether the element, wiring, connection, or control driver is at fault.
Common causes
Most likely first.
- Coolant heater element failure
- Loose or corroded electrical connection
- Damaged wiring
- Fault in the heater control driver
Symptoms
- Check-engine light or coolant-heater warning light
- Longer engine warm-up in cold weather
- Reduced cabin heat during warm-up
How to diagnose it
- Save freeze-frame data and note coolant temperature and heater command state when the performance fault occurred.
- Identify coolant heater A from vehicle service information and inspect its connector and harness for looseness, corrosion, or damage.
- Review live data during a cold start to see whether heater A is commanded and whether coolant temperature responds as expected.
- Test the heater element and its control circuit for correct operation against the manufacturer's specification.
- If the element and wiring pass, check the heater control driver according to the manufacturer's procedure.
Common fixes
- Secure the heater A connector and clean or repair corroded terminals.
- Repair damaged wiring in the coolant heater A circuit.
- Replace coolant heater A if its element fails testing.
- Repair the control driver if testing confirms it is not operating the heater correctly.
Can I keep driving?
Driving is generally possible if engine temperature remains normal, but cold-weather warm-up and cabin heat may be reduced. Allow extra time for defrosting and monitor the temperature gauge.
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.