Severity: Moderate
Drivable, but it can cause more damage or poor economy. Get it checked within days.
What P20EE means
The SCR catalyst is not reducing NOx enough. Often a DEF quality or dosing issue rather than the catalyst itself.
Symptoms
- DEF warning
- Countdown to speed limit on some trucks
Common causes
Most likely first
- 1Poor-quality or contaminated DEF
- 2Crystallized or clogged DEF injector
- 3Failed NOx sensor
- 4Exhaust leak
- 5Aged SCR catalyst
How we diagnose it
- Test DEF concentration with a refractometer
- Run a DEF dosing quantity test
- Compare upstream and downstream NOx sensors
Every vehicle sets codes under its own conditions. We check the factory diagnostic steps and service bulletins for your VIN, so the repair targets the actual cause.