Powertrain, generic (extended)

P20B5 Reductant Metering Unit Heater Control Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Heater element in the metering unit burnt out (usually module replacement)
Broken heater supply or ground wire
Corroded heater terminals at the module connector

Symptoms

  • Warning lamp mainly in cold weather
  • DEF dosing starts late after a cold start
  • Inducement countdown possible

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–1,800
Time1–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

reductant metering unit heater

Related codes

P20B6P20B7P20B8P20B9P202A

References: static.nhtsa.gov, law.cornell.edu, picoauto.com.