P2D20
Reductant System Flow – Blocked
The SCR module detects fully blocked flow in the reductant system. No reductant reaches the injector despite commanded dosing.
- 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.
- Reductant injector cloggedCommon
- Frozen reductant in cold weatherPossible
Parts involved
- Reductant Lines
- Reductant Injector
- Reductant Pump
- SCR Module
P2D20 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.