P20CAReductant Injection Air Pressure Leakage
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- Air-assisted dosing, used mainly on older heavy and medium-duty diesels, mixes diesel exhaust fluid with compressed air from the vehicle's air system and blows the mixture through a nozzle into the exhaust. Airless pump systems in passenger cars and most current light trucks, such as Bosch Denoxtronic 2.2, have no air branch and cannot set this code. P20CA reports that compressed air is escaping from the dosing air circuit: the pressure expected downstream of the air shut-off or pressure control valve fails to hold. CARB names air-assisted injection among the reductant delivery functions that must be monitored. No maker documents P20CA publicly; a Cummins patent for an air-assisted urea doser lists leaks in the air supply, tank and lines as causes of its low-pressure fault. Too low and too high air pressure are P20E6 and P20E7.
- What you may notice
- Check engine light and SCR warning
- Audible hissing near the dosing unit or air lines
- Poor DEF atomisation, higher NOx and later engine derate
- Likely causes
- LikelyLeaking air hose or fitting between air supply and dosing unit
- PossibleWorn seal on the air shut-off or pressure control valve
- PossibleLeak in the vehicle's compressed-air supply feeding the doser
- RareCracked or poorly sealed dosing unit housing on the air side
- 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: €50 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.