Engine Coolant Heater A Control Circuit/Open

Common symptoms

What you'll notice

• Check the coolant heater wiring and connections for any damage or loose connections.
• Inspect the engine coolant heater control circuit fuse and replace if necessary.
• Test the engine coolant heater control circuit relay and replace if it is faulty.
• Verify that the engine coolant heater is receiving power and functioning properly.
• If all else fails, consider replacing the engine coolant heater itself.

Common causes

Most likely first

1. Faulty engine coolant heater control module
2. Open or shorted circuit in the engine coolant heater wiring
3. Malfunctioning engine coolant heater relay
4. Low engine coolant level
5. Defective engine coolant temperature sensor

How to diagnose & fix

Work through it in order

1. Engine overheating
2. Poor heater performance or lack of heat from the heater
3. Check Engine Light (CEL) illuminates
4. Reduced engine power or acceleration
5. Inability to start the engine in cold weather