P20B3Reductant Heater Coolant Control Valve 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
- P20B3 reports a low reading on the control line of the coolant valve that feeds the DEF heating, the classic picture of a control wire shorted to ground or a solenoid with shorted turns. Depending on how the output stage is wired, the valve then stays permanently energised or never responds, so the DEF can get too warm in summer or remain frozen in winter. No manufacturer is known to describe P20B3 publicly; the classification rests on the CARB rule that actuators in the SCR system be checked continuously for circuit faults. The valve exists mainly on coolant-heated systems, where it governs how quickly frozen DEF becomes available. Before replacing it, look for chafed wiring along the frame and for coolant or DEF inside the connector.
- What you may notice
- Malfunction indicator and SCR warning on
- DEF tank overheats or does not thaw, depending on valve position
- Likely causes
- LikelyValve control wire shorted to ground
- PossibleValve solenoid with shorted turns (low resistance)
- RareCoolant or DEF inside the valve connector
- 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.