Powertrain, generic (extended)

P20CA Reductant Injection Air Pressure Leakage

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Leaking air hose or fitting between air supply and dosing unit
Worn seal on the air shut-off or pressure control valve
Leak in the vehicle's compressed-air supply feeding the doser
Cracked or poorly sealed dosing unit housing on the air side

Symptoms

  • Check engine light and SCR warning
  • Audible hissing near the dosing unit or air lines
  • Poor DEF atomisation, higher NOx and later engine derate

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–700
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

reductant air linereductant air pressure control valve

Related codes

P20E6P20E7P20AAP20ABP2037P2038

References: law.cornell.edu, patents.google.com, static.nhtsa.gov.