Engine Coolant Heater A Control Circuit Low

Common symptoms

What you'll notice

• Check the engine coolant level and top up if necessary
• Inspect the engine coolant temperature sensor and replace if faulty
• Check the wiring and connectors for any damage or loose connections and repair or replace as needed
• Test the engine coolant heater control module and replace if defective
• If all else fails, consider replacing the engine coolant heater itself

Common causes

Most likely first

1. Faulty engine coolant heater control module
2. Malfunctioning engine coolant heater relay
3. Defective engine coolant heater sensor
4. Wiring issue or loose connection in the engine coolant heater circuit
5. Low engine coolant level

How to diagnose & fix

Work through it in order

1. Engine overheating
2. Poor heater performance
3. Check Engine Light (MIL) illuminated
4. Reduced engine power
5. Fuel economy decreases