What it means
Reductant Heater B Current Too High: the control module has detected this fault condition. 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 the SCR system can use the fluid in cold conditions. This code sets when the control module detects more current through heater B than expected, which can indicate a shorted heater element or wiring fault.
Common causes
Most likely first.
- Reductant heater element partially shorted
- Short in heater wiring
- Damaged or contaminated connector
- Faulty 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
- Use freeze-frame and live data to confirm when reductant heater B was commanded and whether the excessive-current fault is present.
- Inspect the heater B connector for contamination, damaged terminals, or heat marks and check its harness for pinching or chafing.
- Check the heater B wiring for a short and verify the connector is not bridging adjacent terminals.
- With the circuit isolated according to the manufacturer's procedure, test heater B for an internally shorted element against the manufacturer's specification.
- If the element and wiring pass, check the heater B control circuit for a fault that could cause excess current.
Common fixes
- Repair heater B wiring shorted between conductors or to a power source.
- Clean or replace a contaminated or damaged heater B connector.
- Replace reductant heater B if its element is internally shorted.
- Repair the heater B control circuit if it fails the specified test.
Can I keep driving?
Avoid prolonged driving with an active heater B current fault, especially in freezing weather, because a short can damage the circuit and the DEF may not be heated for SCR dosing. Follow any DEF or NOx warning promptly; some vehicles begin a no-start countdown if the emissions fault remains unresolved.
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.