P20BDReductant Heater B Control Circuit/Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- Heater B's control circuit is open. In GM's tables heater 2 is the DEF line heater; the 2025 version detects the open state with the output off and sets a Type A code after two seconds, while the 2018 version relies on an open status reported by the DEF control module with battery voltage above 11 V. Deutz assigns B to the pressure line heater, the hose from pump to dosing valve. Hino numbers differently: its 2018 bulletin calls P20BD heater 1 of the heated DEF line on J05 cab-overs and asks for a resistance check at the 6-pin connector before the line assembly is replaced. On the Touareg CNRB, VW stores the code when the power stage's diagnostic signal drops below 4.70 V. A frozen pressure line delays or blocks dosing in cold weather. Short circuits of the same element are P20BF and P20C0.
- What you may notice
- Warning lamp, especially after cold nights
- DEF pressure builds slowly or not at all in frost
- Inducement countdown with eventual speed limit
- Likely causes
- LikelyHeating wire in the pressure line broken (line assembly replacement)
- PossibleCorroded or unplugged line heater connector
- PossibleHarness to the line heater damaged along the frame rail
- 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: €80 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.