What it means
Reductant Heater B Current Too Low: 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 the DEF/AdBlue fluid so it can remain usable for SCR dosing in cold conditions. This code sets when the control module detects less current through heater B than expected, which can leave the fluid too cold to dose properly.
Common causes
Most likely first.
- Reductant heater element partially open or degraded
- High resistance in wiring or connector
- Poor power or ground connection
- 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
- Check freeze-frame data and live heater status to see whether reductant heater B was commanded on when its current was low.
- Inspect the heater B connector and wiring for corrosion, loose terminals, heat damage, or chafing.
- Check heater B power and ground connections for poor contact that could restrict current.
- With the circuit isolated as directed by the manufacturer, test heater B for an open or degraded element and compare results with the manufacturer's specification.
- If the heater, wiring, power, and ground pass, check the heater B control circuit using the manufacturer's procedure.
Common fixes
- Clean or repair a poor power or ground connection for reductant heater B.
- Repair damaged or corroded heater B wiring and connector terminals.
- Replace reductant heater B if its element is open or outside specification.
- Repair the heater B control circuit if it fails the specified test.
Can I keep driving?
The vehicle may remain drivable in mild conditions, but cold weather can prevent proper DEF thawing and SCR dosing. Do not ignore a DEF or NOx warning, since emissions faults may lead to a no-start countdown on vehicles that use one.
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.