Powertrain
Definition only
Lights the check engine lamp
P20AA: Reductant Injection Air Pressure Control Valve Stuck Open
Standardized SAE J2012 code · P20xx — Fuel & air metering and auxiliary emission controls
What does P20AA mean?
Reductant air-pressure control valve mechanically stuck open — air pressure cannot be reduced, dosing atomisation off-spec.
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
- 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.
Add your car to see reports of P20AA on the same make and model first.
P20AA in the community
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