What it means
Engine Coolant Heater A Control Circuit/Open: the control circuit is open. Likely a broken wire, disconnected connector, or failed actuator.
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 is an electrically controlled heater used to warm engine coolant on vehicles equipped with this system. The control module monitors heater A's control circuit and sets this code when it detects an open circuit, such as a broken wire or disconnected connection.
Common causes
Most likely first.
- Wiring break
- Pin pushed back out of connector body
- Cracked solder joint inside the module or sensor
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 fault occurred during a cold start or a commanded heater operation.
- Identify coolant heater A and its circuit from vehicle service information, then inspect the connector and harness for disconnection or visible damage.
- Check the connector for pushed-back pins, corrosion, or poor terminal retention.
- Test the heater A control circuit for continuity and check its connections to the heater and control module against the manufacturer's wiring information.
- If the wiring and connections are intact, test the heater element and control driver according to the manufacturer's procedure.
Common fixes
- Reconnect and secure the coolant heater A connector.
- Repair a broken wire or damaged connector terminal in the heater A control circuit.
- Repair a failed connection within a module only if testing confirms the fault there.
- Replace coolant heater A or repair its control driver if testing identifies the failed component.
Can I keep driving?
The vehicle can generally be driven if engine temperature remains normal, but coolant may warm more slowly and cabin heat may be reduced in cold weather. Follow the vehicle's cold-weather guidance if starting or visibility is affected by poor defrosting.
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.