P20B5Reductant Metering Unit Heater 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
- P20B5 concerns the electric heater inside the reductant metering unit, the element that keeps the pump module from freezing. The control unit sets it when this heater circuit is open or otherwise broken. Volkswagen documents the code for the 2014 Touareg 3.0 TDI (engine CNRB): the engine control unit measures the conductance of the element while heating and stores P20B5 at 0.10 siemens or less, roughly 10 ohms or more. A burnt-out element, a broken wire or a corroded terminal are the usual reasons. With the heater dead, DEF in the module stays frozen longer after a cold start and dosing begins late. Too little and too much conductance have separate codes, P20B7 and P20B8, and the tank heater uses its own range.
- What you may notice
- Warning lamp mainly in cold weather
- DEF dosing starts late after a cold start
- Inducement countdown possible
- Likely causes
- LikelyHeater element in the metering unit burnt out (usually module replacement)
- PossibleBroken heater supply or ground wire
- PossibleCorroded heater terminals at the module connector
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €80 – €1,800
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.