P20B7 code meaning
Reductant Metering Unit Heater Control Circuit Low
Powertrain system Generic code P20xx codes Check engine light
What P20B7 means
P20B7 means the metering unit heater circuit reads low. Volkswagen gives this a concrete meaning for the 2014 Touareg CNRB: the control unit checks heater conductance at the start of heating and flags P20B7 below 0.33 siemens, so the element shows more than about 3 ohms; further stages at 0.18 and 0.04 siemens follow. In VW's logic, low therefore refers to conductance, not to voltage, and points to a degraded element, a high-resistance joint or a partly broken wire rather than a short to ground. Other makers may define the low case through the output-stage voltage instead, since their drivers differ. The module receives too little heat, and thawing after a frosty night takes longer.
P20B7 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P20B7
- Warning lamp at the start of a cold-weather heating phase
- DEF dosing delayed in winter
Common causes of P20B7
- Most likelyHeater element resistance too high (aged or partly damaged)
- PossibleContact resistance at the heater terminals
- PossibleHeater wire partly broken (few strands left)
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 P20B7 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. |
| B7 | The exact fault in that area. |
What to do next
- Note P20B7 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 P20B7
What does P20B7 mean?
P20B7 means "Reductant Metering Unit Heater Control Circuit Low". P20B7 means the metering unit heater circuit reads low. It is a generic code, so it means the same on every make.
Is it safe to drive with P20B7?
Drive gently and only to a workshop. With P20B7 the car can go into limp mode (reduced power) to protect itself.
Will P20B7 fail an emissions test?
Yes, it can. P20B7 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 P20B7 to fix?
Difficulty: hard. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P20B7 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.