What it means
Reductant Heater B Sense Circuit: an electrical fault is present in the circuit. The reductant (DEF/AdBlue) heater keeps the urea fluid from freezing; a fault can impair SCR dosing in cold conditions.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Reductant Heater B warms DEF/AdBlue so it can flow when cold, while its sense circuit reports heater temperature or operating feedback to the control module. This code sets when the Heater B sense circuit has an electrical fault, preventing reliable confirmation of Heater B operation.
Common causes
Most likely first.
- Open or damaged heater sense wiring
- Faulty heater temperature sensor
- Loose or corroded connector
- Fault in the reductant heater control circuit
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
- Review freeze-frame data and live reductant-heater readings to confirm the fault is associated with Heater B.
- Inspect Heater B's connector and sense-wire harness for corrosion, loose pins, fluid intrusion, or damage.
- Check the Heater B sense circuit for an open, short, or poor ground, as applicable to the vehicle wiring diagram.
- Measure the temperature sensor or feedback signal at the connector and compare it with the manufacturer's specification.
- If the sense circuit and sensor pass, test Heater B's control circuit and heater operation using the manufacturer's procedure.
Common fixes
- Clean and secure the Heater B connector.
- Repair damaged or open Heater B sense wiring.
- Replace a failed Heater B temperature sensor if it is serviceable separately.
- Repair the Heater B control circuit or replace the faulty heater assembly as indicated by testing.
Can I keep driving?
Driving may be possible in mild conditions, but a failed Heater B sense circuit can impair DEF/AdBlue heating in cold weather and affect emissions control. A NOx warning or no-start countdown may follow, so address any countdown 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.