P01F9
Engine Coolant Heater B Control Circuit Driver Current/Temperature Too High
Generic OBD-II
Common symptoms
What you'll notice
- Replace the Engine Coolant Heater Control Unit
- Inspect and repair any damaged or loose wiring connections in the Engine Coolant Heater circuit
- Check and replace the Engine Coolant Temperature Sensor
- Verify and repair any issues with the Engine Control Module (ECM) related to the Engine Coolant Heater circuit
Common causes
Most likely first
- Faulty engine coolant heater control module
- Short circuit or open circuit in the engine coolant heater control circuit
- Overheating of the engine coolant heater due to continuous operation
- Malfunctioning engine coolant temperature sensor
- Faulty engine coolant heater relay
How to diagnose & fix
Work through it in order
- Engine overheating
- Loss of engine power
- Check Engine Light (CEL) illuminates
- Engine misfires or runs rough
- Poor fuel efficiency
Read & clear P01F9 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.