Powertrain, generic (extended)

P20A1 Reductant Purge Control Valve A Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P20A1 judges the valve by its effect rather than its wiring. When the purge valve switches the pump into reverse, the pressure in the DEF line must drop. GM's 6.6 L Duramax (LML/LGH, tables 14OBDG10 and 16OBDG08) watches this pressure reduction phase: if the pump pressure at its end is less than 50 kPa below the value at its start, the code is stored, Type A, so the MIL comes on in the first trip. Hino describes the same code as a DEF pump reversing valve that stays shut; bulletin SB-16-015 for 2011 to 2017 conventional trucks reports false detections and supplies new DCU software. Real causes are a valve that does not shift, a blocked return path or a pressure sensor that misreads. Electrical faults of the same valve are P20A0, P20A2 and P20A3.

Likely causes

Reversing valve in the supply module not shifting, often from crystallized DEF
Dosing control unit software detecting falsely (Hino SB-16-015)
Return or suction path blocked so pressure cannot drop
DEF pressure sensor reading wrong during the test

Symptoms

  • MIL on after shutdown and restart
  • DEF warning message, possibly with other pump codes
  • Line not emptied, frost damage possible

Repair estimate

DifficultyHardWorkshop job
Parts and labour€0–1,500
Time0.5–3 h

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

Parts involved

reductant purge valve

Related codes

P20A0P20A4P20A5P204BP24DC

References: gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov.