Powertrain, generic (extended)

P24DB Reductant Purge Control Valve B Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

After shut-down an SCR system empties its lines back into the tank so no fluid freezes in them; in Bosch's Denoxtronic 2.2 a 4/2-way valve in the supply module reverses the flow for this. Valve B is a second purge valve, for instance in layouts with two dosing branches. P24DB reports a drive circuit fault of valve B, mostly an interruption. No manufacturer documents P24DB publicly. GM documents the method only for valve A (P20A0) on its 6.6 L diesel: with the low-side driver off, an impedance above 200 kΩ between ECM pin and load for 3 s counts as open, Type A. CARB's heavy-duty rules require all electrical SCR components to be monitored. Shorts are split off as P24DD and P24DE. A line that is not emptied risks frost damage.

Likely causes

Broken wire or unplugged connector to purge valve B
Open solenoid winding in valve B
DEF-induced corrosion in the supply module connector

Symptoms

  • Malfunction indicator lamp on
  • DEF line not purged after shut-off, freezing risk in winter

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–1,500
Time0.5–3 h

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

Parts involved

reductant purge valve b

Related codes

P24DCP24DDP24DEP20A0

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