P20A1 code meaning
Reductant Purge Control Valve A Performance
Powertrain system Generic code P20xx codes Check engine light
What P20A1 means
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.
P20A1 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P20A1
- MIL on after shutdown and restart
- DEF warning message, possibly with other pump codes
- Line not emptied, frost damage possible
Common causes of P20A1
- Most 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
- Less likelyDEF pressure sensor reading wrong during the test
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Reductant purge valve
What each part of P20A1 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 0 | Area: fuel and air metering and auxiliary emission controls. |
| A1 | The exact fault in that area. |
What to do next
- Note P20A1 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P20A1
What does P20A1 mean?
P20A1 means "Reductant Purge Control Valve A Performance". P20A1 judges the valve by its effect rather than its wiring. It is a generic code, so it means the same on every make.
Is it safe to drive with P20A1?
Drive gently and only to a workshop. With P20A1 the car can go into limp mode (reduced power) to protect itself.
Will P20A1 fail an emissions test?
Yes, it can. P20A1 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P20A1 to fix?
Difficulty: hard. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P20A1 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.