What it means
The reductant heater relay control circuit signal is low. The code alone does not confirm a short to ground; the cause depends on the circuit design.
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 carries the module's command for heating the DEF/AdBlue system. This code sets when the circuit signal is lower than expected; the reading can result from a short to ground, excess resistance, or another circuit-design-specific fault and does not prove a ground short.
Common causes
Most likely first.
- Short to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
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 heater command status and warning messages to see under what conditions the low signal was detected.
- Inspect the relay control harness and connectors for chafing, exposed conductors, corrosion, moisture, or loose terminals that could lower the signal.
- Check the circuit signal and relay command with a scan tool or meter using the manufacturer's test procedure, comparing readings with the manufacturer's specification.
- With power isolated as directed, test the control wire for unwanted continuity to ground and check connector contact resistance.
- If the harness and relay circuit test correctly, verify the module's control output and connector condition using the prescribed diagnostic procedure.
Common fixes
- Clean and secure corroded or loose terminals in the heater relay control circuit.
- Repair chafed insulation or a wire shorting to ground.
- Repair a high-resistance connection or damaged harness section.
- Repair or replace a confirmed faulty relay or module control connection.
Can I keep driving?
The vehicle may remain driveable, but the DEF heater may not operate and the emissions system can fail its checks. In cold weather, continued operation with the fault may lead to a no-start countdown; heed any countdown and avoid relying on the vehicle until it is repaired.
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.