P20C0Reductant Heater B Control Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P20C0 reports that heater B's control circuit is high, typically a wire touching a battery feed or a driver that will not switch off. On Ford diesels B is the pressure line heater: with the power stage off, a current below 3 A while the output still carries over 5 V triggers it, and the glow plug module flags the condition in 250 ms. GM's 2025 tables test heater 2 (line heater) with the output off and an elevated voltage window, Type A with a two-second filter; the 2018 tables use a short-to-battery status from the DEF control module. VW uses more than 2.20 A reported by the power stage on the Touareg CNRB, and Deutz FMI 3 for its pressure line heater. A line heater that is powered all the time can overheat the hose, while one the module has shut down leaves it frozen.
- What you may notice
- Malfunction indicator lamp and DEF warning
- Line heater may stay on with the engine off, draining the battery
- Frozen pressure line once the module disables the heater
- Likely causes
- LikelyLine heater control wire shorted to a positive feed
- PossibleHeater output stage in the DEF, engine or glow plug module stuck on
- RareBridged pins in a shared connector next to a supply terminal
- 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.