P20CA code meaning
Reductant Injection Air Pressure Leakage
Powertrain system Generic code P20xx codes Check engine light
What P20CA means
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.
P20CA at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P20CA
- Check engine light and SCR warning
- Audible hissing near the dosing unit or air lines
- Poor DEF atomisation, higher NOx and later engine derate
Common causes of P20CA
- Most 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
- Less likelyCracked or poorly sealed dosing unit housing on the air side
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Reductant air lineReductant air pressure control valve
What each part of P20CA means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 0 | Area: fuel and air metering and auxiliary emission controls. |
| CA | The exact fault in that area. |
What to do next
- Note P20CA and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P20CA
What does P20CA mean?
P20CA means "Reductant Injection Air Pressure Leakage". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P20CA?
Drive gently and only to a workshop. With P20CA the car can go into limp mode (reduced power) to protect itself.
Will P20CA fail an emissions test?
Yes, it can. P20CA is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P20CA to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P20CA clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.