What it means
DEF heater A current draw exceeds the upper threshold — typically a partial short in the heating element.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Reductant heater A warms DEF (AdBlue) so it can flow through the SCR emissions system in cold conditions. The controller monitors heater A’s current and sets this code when the draw is above its upper limit, often because the element or its wiring has a partial short.
Common causes
Most likely first.
- Reductant heater A element partially shorted
- Damaged heater wiring or connector
- Faulty heater control circuit
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
How to diagnose it
- Record freeze-frame data and check SCR, heater, DEF, and NOx codes to determine when heater A was commanded and the ambient conditions.
- Use scan-tool data to compare heater A’s commanded state and current with other available heater readings.
- Inspect heater A’s connector and wiring for chafing, melted insulation, corrosion, or fluid intrusion.
- Test heater A’s resistance and circuit for shorts using the manufacturer’s procedure and specification.
- If wiring passes, test the heater control circuit and module output before condemning the heater element.
Common fixes
- Repair damaged or shorted heater A wiring and connector terminals.
- Replace heater A if its element fails the manufacturer’s electrical checks.
- Repair a faulty heater control circuit if testing confirms the control fault.
- Clear the code and confirm heater current is within specification when commanded.
Can I keep driving?
The vehicle may continue to run, but DEF heating and emissions control can be impaired; some vehicles may begin a no-start countdown if the fault remains. Repair it promptly, especially before cold weather or if a dashboard countdown appears.
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.