P20B4Reductant Heater Coolant Control Valve 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
- P20B4 is the opposite electrical case to P20B3: the drive circuit of the reductant heater coolant valve reads too high, which points to a short to battery voltage on the control line or, with certain driver designs, an interrupted ground return. The control unit can then no longer switch the valve, and the heating loop stays in whatever position the valve spring holds. On coolant-heated installations, such as Bosch supply modules supplied with a cooling-water heating option, that decides whether the module thaws at all. No manufacturer documents P20B4 publicly; CARB's comprehensive component rules form the basis. Measure with the valve connected, because some controllers cut the output after a fault, as Hino describes for its valve.
- What you may notice
- Malfunction indicator and SCR warning on
- Valve cannot be actuated in an output test
- Slow DEF thaw in winter
- Likely causes
- LikelyValve control wire shorted to battery voltage
- PossibleOpen ground return of the valve circuit
- RareOutput stage in the control unit defective
- 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 – €800
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.