P20A4: Reductant Purge Control Valve A Stuck Open
Standardized SAE J2012 code · P20xx — Fuel & air metering and auxiliary emission controls
What does P20A4 mean?
Reductant purge control valve A is mechanically stuck open — system cannot maintain dosing pressure because the line is constantly vented to the tank.
The code tells you which monitor failed, not which part is broken. Test before replacing parts.
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)
Common causes
- High Valve stuck open mechanically
- Low Carbon or debris buildup preventing free movement
- Low Component wear with age - mechanical play
Likelihood is a general estimate across vehicles; your make and model may differ.
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P20A4 in the community
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