What it means
Reductant Heater B Sense Circuit Low: the signal voltage is below the expected range. 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 fluid can remain usable in freezing conditions. The controller monitors heater B's sense circuit, and this code sets when its signal is below the expected range, which can point to a short to ground or a corroded connection.
Common causes
Most likely first.
- Sense line shorted 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
- Save freeze-frame data and check live data for reductant heater B's sense value and any related DEF temperature or heater status.
- Inspect heater B's connector and harness for corrosion, moisture, pin damage, or insulation rubbed through to ground.
- With the circuit powered down as directed by the service information, check the sense wire for an unintended connection to ground.
- Check connector contact and wiring continuity from heater B to the controller, looking for corroded terminals or damaged wire.
- Compare heater B sense-circuit readings with the manufacturer's specifications and test the heater or controller only after the wiring checks.
Common fixes
- Repair chafed insulation or a sense wire shorted to ground.
- Clean or replace corroded connector terminals and restore a sound seal.
- Repair an open or damaged section of the heater B sense wiring.
- Replace the reductant heater B assembly if its sense circuit fails testing.
Can I keep driving?
You may be able to drive normally at first, but cold weather can prevent proper DEF thawing and impair SCR emissions control. Heed any DEF warning or no-start countdown and address the fault before the countdown expires.
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.