P20CA
Reductant Injection Air Pressure Leakage
A leak has been detected in the air-assist branch of the DEF system — pressure decays faster than allowed when the air pump shuts off.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
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
Ordered by how often each turns out to be the cause.
- Cracked air line or fittingCommon
- Air pressure control valve seat leaksPossible
Parts involved
- Reductant Air Line
- Reductant Air Pressure Control Valve
P20CA is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.