P20A1Reductant Purge Control Valve A Performance
- 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
- P20A1 judges the valve by its effect rather than its wiring. When the purge valve switches the pump into reverse, the pressure in the DEF line must drop. GM's 6.6 L Duramax (LML/LGH, tables 14OBDG10 and 16OBDG08) watches this pressure reduction phase: if the pump pressure at its end is less than 50 kPa below the value at its start, the code is stored, Type A, so the MIL comes on in the first trip. Hino describes the same code as a DEF pump reversing valve that stays shut; bulletin SB-16-015 for 2011 to 2017 conventional trucks reports false detections and supplies new DCU software. Real causes are a valve that does not shift, a blocked return path or a pressure sensor that misreads. Electrical faults of the same valve are P20A0, P20A2 and P20A3.
- What you may notice
- MIL on after shutdown and restart
- DEF warning message, possibly with other pump codes
- Line not emptied, frost damage possible
- Likely causes
- LikelyReversing valve in the supply module not shifting, often from crystallized DEF
- PossibleDosing control unit software detecting falsely (Hino SB-16-015)
- PossibleReturn or suction path blocked so pressure cannot drop
- RareDEF pressure sensor reading wrong during the test
- 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: €0 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.