P24DFReductant Purge Control Valve B Stuck Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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.
- What you may notice
- Malfunction indicator lamp on
- DEF pressure too low, reduced dosing and rising NOx
- Warnings about reduced SCR function, possibly later engine power limits
- Likely causes
- LikelyInternal leak or worn seat in purge valve B
- PossibleDEF crystals preventing the valve from returning to dosing position
- RareControl circuit fault keeping the valve energised
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €300 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.