Powertrain, generic (extended)

P20A2 Reductant Purge Control Valve A Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

The purge valve that reverses the DEF flow at shutdown is usually switched on the ground side. P20A2 reports that its control line is pulled too low, typically a short to ground somewhere between the driver and the coil, which would switch the valve on unintentionally or keep the driver from sensing it. GM tests the low-side driver of the 6.6 L Duramax with the output off and sets P20A2 when the impedance to controller ground is under 0.5 Ω for 2 s, Type A. Volkswagen flags the Touareg 3.0 TDI (CNRB, 2014) when the power-stage voltage falls below 2.97 V. Compared with P20A0, where the line is open, the fault here is an unwanted connection to ground. Chafed wiring near the tank and water in the connector are the usual findings; the controller may then block dosing.

Likely causes

Control wire chafed against the frame or tank bracket
Moisture or DEF in the valve connector creating a leakage path
Valve coil shorted to its housing

Symptoms

  • MIL on at once (GM Type A)
  • Service emission or DEF system message
  • Dosing possibly disabled

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–1,200
Time0.5–3 h

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

Parts involved

reductant purge valve

Related codes

P20A0P20A3P20A1P24DD

References: gsi.ext.gm.com, static.nhtsa.gov, law.cornell.edu.