P20BFReductant Heater B Control Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- For heater B the code stands for a grounded control circuit or an overcurrent. Ford, where B is the pressure line heater, sets it when circuit 2 draws more than 15 A with the power stage on; the glow plug module can report such a short within 250 ms. GM's 2025 DEF module applies to heater 2 (line heater) the same low-band and overcurrent tests it uses on the tank heater, Type A, confirmed within 2 s, and in 2018 relied on a short-to-ground status from the DEF control module. VW's Touareg CNRB stores P20BF below 2.97 V signal voltage; Deutz lists FMI 4, a voltage too low, for its pressure line heater. Chafed line harnesses along the frame and water in connectors are typical. Because the driver shuts down or a fuse fails, the pressure line stays unheated in winter.
- What you may notice
- Check engine light, sometimes with a blown fuse
- DEF pressure fault codes in cold weather
- Speed limitation if the fault persists
- Likely causes
- LikelyLine heater wire chafed on the frame and grounded
- PossibleWater in the line heater connector creating a path to ground
- PossibleInternal short in the heated pressure line
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €60 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.