P20B6Reductant Metering Unit Heater Control Circuit Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- P20B6 is the functional check of the metering unit heater circuit: wiring and driver pass the electrical tests, yet the heating falls short of what the control unit expects, for instance the module temperature barely rises during a commanded heating phase or the current drifts away from its target. Such a monitor needs the heater to be running, so it can only reach a verdict in cold conditions and across a drive cycle. Volkswagen's Touareg CNRB chart lists P20B5, P20B7 and P20B8 for this heater but no P20B6, and no other maker publishes the code with limits. Suspects include an aged element with changed resistance, poor thermal contact inside the module or a temperature sensor feeding a false value.
- What you may notice
- Warning lamp after cold starts only
- Long delay before DEF dosing begins in frost
- Likely causes
- LikelyAged heater element with reduced output
- PossibleMetering unit temperature sensor reporting a wrong value
- RareLow supply voltage to the heater (weak battery, poor ground)
- 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.