What it means
This code indicates a low 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 heats a downstream portion of the DEF supply line. The control module monitors voltage in heater B’s control circuit and sets this code when it is lower than expected, which can indicate a short to ground or resistance in the connector or wiring.
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
- Record freeze-frame data and check for related heater circuit codes that may indicate a shared power or ground issue.
- Inspect heater B’s line-mounted connector and harness for rubbed insulation, corrosion, moisture, or loose or pushed-back terminals.
- Check the heater B control circuit for a short to ground using the manufacturer’s wiring diagram and isolation procedure.
- Measure voltage drop across heater B’s power and ground connections while the heater is commanded on, comparing results with the manufacturer’s specification.
- Test the heater B element and relay, then check the module control side if the wiring and connections are sound.
Common fixes
- Repair chafed heater B wiring that has shorted to ground.
- Clean or replace corroded, loose, or damaged heater B connector terminals.
- Restore a poor power or ground connection in the heater B circuit.
- Replace a confirmed failed heater B element or relay.
Can I keep driving?
A short drive may be possible if the vehicle behaves normally, but heater B may not keep its line section warm enough for DEF flow in freezing weather. Take NOx warnings and any no-restart countdown seriously, as the vehicle may eventually be restricted from restarting.
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.