What it means
The control module monitors whether reductant heater C responds as expected when commanded. It sets this code when the heater’s measured performance, such as its warming response, falls outside the calibrated range; the code does not by itself identify the cause.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Reductant heater C heats a monitored portion of the DEF system to help maintain fluid flow in cold conditions. The control module checks heater C’s electrical operation and temperature response, setting this code when its warming performance falls outside the expected range even though the circuit may not be open.
Common causes
Most likely first.
- Heater C partly failed
- Corroded or loose electrical connections
- Damaged wiring
- Poor heat transfer or excessive heat loss
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 compare heater C’s temperature readings with ambient conditions and other available reductant temperatures.
- Inspect the heater C assembly and nearby line or tank section for damage, poor insulation, or conditions that could cause heat loss.
- Check heater C’s connector and wiring for corrosion, loose terminals, chafing, or heat damage.
- Command heater C on with a scan tool where supported and monitor the temperature response over the specified test period.
- Measure heater C current or voltage drop under load as directed by the manufacturer and compare with its specification.
- If electrical tests pass, check the heater C temperature sensor and heat transfer path before suspecting a module fault.
Common fixes
- Repair loose or corroded heater C connections.
- Repair damaged heater C wiring or insulation.
- Replace a partially failed heater C element or assembly after confirming weak output.
- Repair poor insulation or heat transfer around the heater C section.
Can I keep driving?
The vehicle may be usable in mild weather, but heater C may not keep its DEF section warm enough in freezing conditions. Heed any NOx warning or no-restart countdown because poor DEF delivery can affect emissions control and eventually restrict 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.