P24FF
Reductant Temperature Too High
The temperature of the AdBlue/DEF in the dosing system exceeds the safe limit — risk of thermal decomposition (NH3/biuret formation) and clogged dosing nozzles. Often caused by a stuck-on tank heater, a stalled coolant return or proximity to a hot exhaust component.
- 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.
- Tank heater stuck onCommon
- Heat soak from exhaust or engine bayPossible
Parts involved
- Reductant Tank
- Reductant Tank Heater
- Reductant Lines
P24FF 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.