P20ABReductant Injection Air Pressure Control Valve Stuck Closed
- 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
- The opposite of P20AA: the air pressure control valve does not open although the controller commands it, so no atomizing air reaches the DEF dosing point. The air pressure sensor stays near ambient during dosing requests. Without air, an air-assisted dosing module cannot spray the fluid into fine droplets, and the risk of liquid DEF and deposits in the exhaust grows; controllers therefore stop dosing, NOx rises and heavy vehicles move toward a derate. No manufacturer documents P20AB publicly; Deutz files low air pressure under its own code P1124 and a blocked air path at the injector under P1123. Before condemning the valve, check the supply pressure from the vehicle air system, a frozen or kinked line and the air filter. P20A6 to P20A9 indicate electrical causes instead.
- What you may notice
- MIL or SCR warning on
- Air pressure stays at zero when dosing is requested
- Power derate or inducement on trucks
- Likely causes
- LikelyValve seized by corrosion or deposits
- PossibleNo supply pressure, for example low air reservoir or closed protection valve
- PossibleAir line frozen with condensate or kinked
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.