What it means
The module monitors the control circuit for engine coolant heater B and sets this code when its operation falls outside the expected performance range. The code identifies a circuit performance problem, but does not specify the failed part.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Engine Coolant Heater B helps warm the engine coolant, and the control module checks whether its electrical operation matches the commanded behavior. This code means heater B's circuit performance is outside the expected range; it does not by itself identify whether the heater, wiring, connection, or driver is at fault.
Common causes
Most likely first.
- Coolant heater element failure
- Loose or corroded electrical connection
- Damaged wiring
- Fault in the heater control driver
Symptoms
- Check-engine light or coolant-heater warning light
- Longer engine warm-up in cold weather
- Reduced cabin heat during warm-up
How to diagnose it
- Review freeze-frame data and heater B command or status live data to establish when the performance fault occurred.
- Inspect heater B's connector and wiring for looseness, corrosion, chafing, heat damage, or a broken conductor.
- Check the heater element and its electrical connections using the manufacturer's test procedure.
- Measure the control circuit for continuity and excessive resistance while checking the connector terminals for poor contact.
- If the heater and circuit pass their checks, investigate the module's heater B control driver.
Common fixes
- Clean and secure a loose or corroded heater B connection.
- Repair damaged wiring or replace faulty connector terminals in the heater B circuit.
- Replace a heater B element that fails the manufacturer's test.
- Repair or replace the control module if its heater B driver is confirmed faulty.
Can I keep driving?
You can generally continue driving, but cold-weather warm-up may take longer and cabin heat may be reduced. Plan for slower window defrosting until heater B is operating correctly.
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.