P24DCReductant Purge Control Valve B Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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.
- What you may notice
- Malfunction indicator lamp on
- Frozen DEF line or dosing fault after cold nights
- Likely causes
- LikelyValve B mechanically stuck by crystallised DEF
- PossibleBlocked return path or filter in the supply module
- RareDEF pressure sensor reading incorrectly
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €150 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.