Powertrain, generic (extended)

P24DF Reductant Purge Control Valve B Stuck Open

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

Stuck open means purge valve B remains in, or leaks toward, its emptying position while the system should be dosing. Part of the pump flow then goes back to the tank, so working pressure builds slowly, drops quickly when the pump stops, or needs a high pump duty to hold. No manufacturer documents P24DF publicly, and the public GM tables cover only the opposite failure of valve A (no pressure drop in purge, P20A1). The Denoxtronic 2.2 layout described by Pico explains the mechanism: one 4/2-way valve decides whether the pump feeds the injector or sucks the line empty, so a valve hanging halfway shortcuts the pressure side. CARB requires SCR delivery faults to be detected before emissions rise. P24E0 is the opposite fault; P24DC the general function test.

Likely causes

Internal leak or worn seat in purge valve B
DEF crystals preventing the valve from returning to dosing position
Control circuit fault keeping the valve energised

Symptoms

  • Malfunction indicator lamp on
  • DEF pressure too low, reduced dosing and rising NOx
  • Warnings about reduced SCR function, possibly later engine power limits

Repair estimate

DifficultyHardWorkshop job
Parts and labour€300–1,500
Time1–4 h

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

Parts involved

reductant purge valve b

Related codes

P24E0P24DCP20A4

References: picoauto.com, law.cornell.edu, gsi.ext.gm.com.