Mercedes-Benz, Audi Warning Message
“AdBlue Malfunction”
The diesel exhaust fluid (DEF/AdBlue) system has detected a fault. The SCR system cannot properly reduce NOx emissions. If ignored, the vehicle may enter a speed-limited mode or refuse to restart after the next shutoff.
moderate severity
Common Causes
- AdBlue quality degradation (crystallization)
- DEF injector clogging or failure
- AdBlue pump or heating element failure
- NOx sensor malfunction
- AdBlue tank level sensor fault
Immediate Action
Refill AdBlue if low. If the message persists after refill, the system has a component fault. Schedule service before the countdown timer reaches zero — the vehicle will not restart once the limit is reached.
Typical Repair Cost
$300–$3,000