Powertrain, generic (extended)

P24DC Reductant Purge Control Valve B Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P24DC judges purge valve B by its effect, not by its wiring: once the controller switches the valve to purge, the pressure in the DEF line it serves should fall noticeably, and here it did not. No manufacturer documents P24DC publicly. On the 6.6 L Duramax, GM tests valve A under P20A1: if, when the pressure reduction phase ends, the pump pressure is less than 50 kPa below its starting value, the fault is set, Type A, sampled every 100 ms. Pico's description of the Denoxtronic 2.2 explains why: in purge mode the reversing valve makes the pump pull fluid out of the line, so a vacuum should build. A valve that does not shift, a blocked return or a misreading pressure sensor all end here. Electrical faults of valve B are P24DB, P24DD and P24DE.

Likely causes

Valve B mechanically stuck by crystallised DEF
Blocked return path or filter in the supply module
DEF pressure sensor reading incorrectly

Symptoms

  • Malfunction indicator lamp on
  • Frozen DEF line or dosing fault after cold nights

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€150–1,500
Time1–3 h

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

Parts involved

reductant purge valve b

Related codes

P24DBP24DFP24E0P20A1

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