What it means
The reductant heater relay control circuit signal is high. The code alone does not confirm a short to B+; 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 higher than expected; a short to battery voltage is one possibility, but the circuit design and fault require testing to confirm.
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
- Read freeze-frame data and related reductant-system codes, then check heater command status and warning messages to establish when the high signal was detected.
- Inspect the relay control harness for pinched or chafed wiring that could contact a power source, and check connectors for corrosion or loose terminals.
- Measure the control signal during the commanded and uncommanded states using the manufacturer's procedure, comparing it with the manufacturer's specification.
- With power isolated as directed, check the control wire for unwanted continuity to a supply circuit and inspect connector terminals for bridging or damage.
- If wiring and relay checks pass, test the module control output and connector condition using the manufacturer's diagnostic procedure.
Common fixes
- Repair a pinched or chafed control wire contacting a power source.
- Clean, secure, or replace damaged relay control connector terminals.
- Repair a harness fault causing the signal to remain high.
- Repair or replace a confirmed faulty relay or module control connection.
Can I keep driving?
The vehicle may remain driveable, but the DEF heater control and emissions monitoring may not work correctly. In cold weather, a persistent fault can contribute to an emissions-related no-start countdown; follow any countdown displayed and arrange repair promptly.
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.