P20B1Reductant Heater Coolant Control Valve 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
- Many heavy-duty SCR systems thaw the DEF tank and supply module with engine coolant, and an electrically switched valve decides when that warm coolant may circulate; Bosch offers its larger supply modules with either electric or cooling-water heating. P20B1 is set when the control unit finds the drive circuit of this valve open or otherwise defective. No manufacturer documents P20B1 publicly. Hino, which fits such a coolant cutoff valve, explains in TT-16-014 that once its dosing control unit detects an open load it stops powering the valve until a UREA SCR memory reset, so circuit tests only work while the valve stays connected. Without a working valve, DEF stays frozen longer in winter.
- What you may notice
- Malfunction indicator and SCR warning on
- DEF thaws slowly or not at all in cold weather
- Valve does not click during an actuator test
- Likely causes
- LikelyValve connector unplugged, loose or corroded
- PossibleOpen solenoid coil in the coolant valve
- PossibleBroken wire between control unit and valve
- 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 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.