P20B5 code meaning
Reductant Metering Unit Heater Control Circuit/Open
Powertrain system Generic code P20xx codes Check engine light
What P20B5 means
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.
P20B5 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P20B5
- Warning lamp mainly in cold weather
- DEF dosing starts late after a cold start
- Inducement countdown possible
Common causes of P20B5
- Most likelyHeater element in the metering unit burnt out (usually module replacement)
- PossibleBroken heater supply or ground wire
- PossibleCorroded heater terminals at the module connector
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 P20B5 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. |
| B5 | The exact fault in that area. |
What to do next
- Note P20B5 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 P20B5
What does P20B5 mean?
P20B5 means "Reductant Metering Unit Heater Control Circuit/Open". P20B5 concerns the electric heater inside the reductant metering unit, the element that keeps the pump module from freezing. It is a generic code, so it means the same on every make.
Is it safe to drive with P20B5?
Drive gently and only to a workshop. With P20B5 the car can go into limp mode (reduced power) to protect itself.
Will P20B5 fail an emissions test?
Yes, it can. P20B5 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 P20B5 to fix?
Difficulty: hard. A typical repair takes 1 to 3 hours of work. This is a job for a workshop.
Will P20B5 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.