What it means
Engine Coolant Heater B Control Circuit High: the control-circuit voltage is above the expected range. Often an open circuit or a short to supply voltage.
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 is controlled through an electrical circuit monitored by the engine module. This code sets when the module detects voltage higher than expected on heater B's control circuit, including when the circuit is open or connected to a power source.
Common causes
Most likely first.
- Wiring shorted to battery
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
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
- Use freeze-frame and heater B live data to identify when the high reading occurred and whether the module had commanded the heater.
- Inspect heater B's harness and connector for a wire pinched against a power feed, loose connection, or visible damage.
- Check connector terminals for corrosion, poor contact, or a pin that is not seated properly.
- Test the control circuit for a short to battery voltage and check for an open connection using the manufacturer's procedure.
- If the circuit wiring is sound, check heater B and the module's control output for a fault.
Common fixes
- Secure a loose heater B connector and correct poor terminal contact.
- Repair a wire shorted to a power feed or trapped against a B+ source.
- Replace damaged terminals or the affected harness section.
- Replace a confirmed failed heater element or repair a faulty control-module output.
Can I keep driving?
Driving is generally possible, though heater B may not warm the engine coolant, especially affecting warm-up and cabin heat in cold weather. Make sure the windows can be kept clear before driving.
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.