P01F9
Engine Coolant Heater B Control Circuit Driver Current/Temperature Too High
Engine Coolant Heater B Control Circuit Driver Current/Temperature Too High: the component is overheating, typically from extended load or slip.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Symptoms
- Check engine light on
- Cooling fan runs constantly or not at all
- Cabin heater weak or excessively hot
- Possible long warm-up time or hard cold start
Common causes
Ordered by how often each turns out to be the cause.
- Short circuit in heater wiring or elementCommon
Parts involved
- Coolant Heater B
- Heater Driver
P01F9 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.