What it means
Engine Coolant Heater A Control Circuit Low: the control-circuit voltage is below the expected range. Often a short to ground or high resistance in the wiring.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Engine coolant heater A warms coolant when the control module commands it, and the module monitors the heater's control circuit. This code sets when that circuit's voltage is below the expected range, which can result from a short to ground or excessive resistance; it concerns heater A specifically.
Common causes
Most likely first.
- Wiring shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Check engine light on
- Coolant may take longer to warm up
- Cabin heat may be reduced
- Cold-weather starting or warm-up may be affected
How to diagnose it
- Save freeze-frame data and check whether the low-circuit fault occurred during a command to operate coolant heater A.
- Identify heater A and inspect its wiring for chafing, crushed sections, or contact with ground.
- Check the heater A connector for corrosion, moisture, loose terminals, or other resistance-raising damage.
- Test the control circuit for a short to ground and check connection resistance using the manufacturer's circuit information.
- If the wiring and connectors are sound, test the heater element and control driver according to the manufacturer's procedure.
Common fixes
- Repair wiring chafed through to ground in the heater A control circuit.
- Clean corroded terminals or repair a loose heater A connection.
- Repair damaged circuit wiring or terminals that create excessive resistance.
- Replace coolant heater A or repair its control driver if testing confirms the component fault.
Can I keep driving?
You can generally drive if engine temperature is normal, but coolant and cabin heat may take longer to warm in cold conditions. Allow extra time for defrosting, and do not drive if reduced visibility makes the trip unsafe.
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.