P20B6 code meaning
Reductant Metering Unit Heater Control Circuit Performance
Powertrain system Generic code P20xx codes Check engine light
What P20B6 means
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.
P20B6 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 4 hours
- Clears after repairAfter a drive cycle
Symptoms of P20B6
- Warning lamp after cold starts only
- Long delay before DEF dosing begins in frost
Common causes of P20B6
- Most likelyAged heater element with reduced output
- PossibleMetering unit temperature sensor reporting a wrong value
- Less likelyLow supply voltage to the heater (weak battery, poor ground)
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Reductant metering unit heater
What each part of P20B6 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 0 | Area: fuel and air metering and auxiliary emission controls. |
| B6 | The exact fault in that area. |
What to do next
- Note P20B6 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P20B6
What does P20B6 mean?
P20B6 means "Reductant Metering Unit Heater Control Circuit Performance". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P20B6?
Drive gently and only to a workshop. With P20B6 the car can go into limp mode (reduced power) to protect itself.
Will P20B6 fail an emissions test?
Yes, it can. P20B6 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P20B6 to fix?
Difficulty: hard. A typical repair takes 1 to 4 hours of work. This is a job for a workshop.
Will P20B6 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.