OBD-II code · Powertrain (generic, extended)
P20A4 Reductant Purge Control Valve A Stuck Open
Reductant purge control valve A is mechanically stuck open — system cannot maintain dosing pressure because the line is constantly vented to the tank.
Is it safe to drive with P20A4?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyValve stuck open mechanically
- Less likelyCarbon or debris buildup preventing free movement
- Less likelyComponent wear with age - mechanical play
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.7–3 h
- Emissions test
- Likely to fail
- Parts involved
- Reductant Purge Valve
Related codes
- P20A0Reductant Purge Control Valve A Circuit/Open
- P24DFReductant Purge Control Valve B Stuck Open
- P20A1Reductant Purge Control Valve A Performance
- P20A2Reductant Purge Control Valve A Circuit Low
- P20A3Reductant Purge Control Valve A Circuit High
- P20A5Reductant Purge Control Valve A Stuck Closed
- P20A6Reductant Injection Air Pressure Control Valve Circuit/Open
- P20A7Reductant Injection Air Pressure Control Valve Performance
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.