What it means
This code indicates a high voltage condition in reductant heater B'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 B warms a downstream section of the DEF line to support fluid delivery in cold conditions. The control module monitors heater B’s control-circuit voltage and sets this code when the voltage is higher than expected, commonly when the wire 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
- Save freeze-frame data and check for other heater circuit codes that may help identify a shared wiring fault.
- Inspect heater B’s harness and connector for pinched insulation, corrosion, loose terminals, or contact with a power feed.
- Follow the manufacturer’s wiring diagram to test whether heater B’s control wire is shorted to B+.
- Check circuit voltage with heater B commanded both on and off, using the manufacturer’s procedure to locate the source of the high reading.
- If the harness checks out, test heater B’s relay and module output against the manufacturer’s specification.
Common fixes
- Repair heater B wiring pinched against a battery-positive source.
- Replace a harness section with insulation damaged by a B+ short.
- Clean or replace damaged heater B connector terminals.
- Replace a confirmed faulty relay or module output component after testing the circuit.
Can I keep driving?
If there are no drivability symptoms, a short trip may be possible, but heater B may not keep its DEF line section warm in freezing conditions. Avoid relying on the vehicle in severe cold and heed any no-restart countdown, since DEF delivery and emissions control may be affected.
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.