What it means
The reductant heater relay control circuit is open or has an open-circuit fault. The code does not specify which component or connection is responsible.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The reductant heater relay control circuit lets the vehicle command heating for the DEF/AdBlue system in cold conditions. This code sets when the module detects an open circuit in the relay control path, such as a break in wiring, a poor terminal connection, or an open relay coil.
Common causes
Most likely first.
- Relay coil open
- Pin pushed back out of connector body
- Cracked solder joint inside the module or sensor
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
- Read freeze-frame data and related reductant-system codes, then check warning messages and heater command status to establish when the open-circuit fault occurred.
- Inspect the reductant heater relay and its connectors for loose or backed-out pins, corrosion, heat damage, or broken wires.
- With the circuit de-energized as directed by the service information, check the relay coil and control-path continuity against the manufacturer's specification.
- If the relay checks correctly, test continuity through the control wire between the relay and module, flexing the harness gently to reveal an intermittent open.
- Check module connector terminals and any accessible internal control connections only as directed by the manufacturer's diagnostic procedure.
Common fixes
- Reseat or repair a backed-out, corroded, or damaged relay connector terminal.
- Repair an open or broken wire in the heater relay control circuit.
- Replace the relay if its coil is confirmed open.
- Repair a confirmed module-side connection fault following the manufacturer's procedure.
Can I keep driving?
You can usually drive if the engine runs normally, but the DEF heater may not work and emissions warnings can remain active. In cold weather, a continuing fault may trigger an emissions-related no-start countdown, so address it promptly and follow any countdown shown by the vehicle.
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.