What it means
This code indicates a high voltage condition in reductant heater A's control circuit.
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 in the tank or a heated section so the SCR system can use the fluid in cold weather. The control module monitors heater A’s control-circuit voltage and sets this code when voltage is higher than expected, often because the circuit is shorted to battery power.
Common causes
Most likely first.
- Short to B+
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
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 for related heater circuit codes that could point to a shared wiring or supply issue.
- Inspect heater A’s harness and connector for pinched wires, damaged insulation, corrosion, or terminals contacting a power source.
- Use the manufacturer’s wiring diagram to check whether the heater A control wire is shorted to battery voltage.
- Compare circuit voltage with the heater commanded on and off, following the manufacturer’s test procedure to locate where the high voltage remains.
- If the wiring checks out, test the heater A relay and module control output according to the manufacturer’s specification.
Common fixes
- Repair a heater A wire that is pinched against a battery-positive feed.
- Replace damaged harness sections that have shorted to B+.
- Clean or replace corroded or damaged heater A connector terminals.
- Replace a confirmed faulty relay or module only after its circuit and output have been tested.
Can I keep driving?
If the vehicle runs normally, a short trip may be possible, but heater A may not warm its DEF section as intended. Cold weather can prevent proper reductant delivery, and ignoring a no-restart countdown can leave the vehicle unable to restart.
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.