What it means
Engine Coolant Heater A Control Circuit High: the control-circuit voltage is above the expected range. Often an open circuit or a short to supply voltage.
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 coolant when commanded, while the control module monitors voltage in its control circuit. This code sets when circuit voltage is higher than expected, often because the circuit is open or shorted to a supply; it identifies heater A's circuit.
Common causes
Most likely first.
- Wiring shorted to battery
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
Symptoms
- Check engine light on
- Coolant may take longer to warm up
- Cabin heat may be reduced
- Cold-weather starting or warm-up may be affected
How to diagnose it
- Record freeze-frame data and note whether the high-circuit fault appeared when coolant heater A was commanded on or off.
- Identify heater A and inspect its harness for broken wires, disconnected plugs, or contact with a power source.
- Check connector terminals for corrosion, pushed-back pins, or poor contact.
- Test the heater A control circuit for an open and for a short to supply voltage, following the manufacturer's wiring information.
- If circuit continuity and isolation are correct, test the heater element and control driver according to the manufacturer's procedure.
Common fixes
- Reconnect a disconnected coolant heater A connector.
- Repair an open wire in the heater A control circuit.
- Repair wiring shorted to supply voltage.
- Replace coolant heater A or repair its control driver if testing confirms the failed component.
Can I keep driving?
The code usually affects cold-weather warm-up rather than immediate engine temperature, so driving may be possible if the engine temperature is normal. Expect reduced cabin heat and allow extra time for defrosting before driving.
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.