What it means
This code indicates a low voltage condition in reductant heater C'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 C warms a monitored part of the DEF system so the fluid remains usable in cold weather. The control module monitors voltage in heater C’s control circuit and sets this code when voltage is lower than expected, which can result from a short to ground or high resistance in the circuit.
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 other heater circuit codes that could indicate a shared power or ground problem.
- Inspect heater C’s connector and harness for chafing, exposed conductors, corrosion, moisture, or loose terminals.
- Test the heater C control circuit for a short to ground using the manufacturer’s wiring diagram and isolation procedure.
- Measure voltage drop at heater C’s power and ground connections while it is commanded on, and compare with the manufacturer’s specification.
- Test the heater C element and relay, then check the module control circuit if the wiring and connections pass.
Common fixes
- Repair heater C harness insulation that has rubbed through to ground.
- Clean or replace corroded or loose heater C connector terminals.
- Repair a poor power or ground connection in the heater C circuit.
- Replace a failed heater C element or relay after confirming the fault.
Can I keep driving?
A short drive may be possible if the vehicle has no other symptoms, but heater C may not warm its DEF section adequately in freezing conditions. Monitor warnings and heed any no-restart countdown, since DEF delivery and emissions control can be impaired and restarting may eventually be restricted.
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.