Urgency: Moderate
DEF / AdBlue Warning Light
Investigate soon. Driving short distances is generally okay, but book a diagnostic check.
What the DEF / AdBlue Warning Light Means
On your diesel your car, this light means the AdBlue tank needs topping up. Modern diesels will progressively limit and then block restart once DEF runs out, so refill promptly.
Common Causes
- Low diesel exhaust fluid level (normal)
- DEF quality/contamination
- Faulty DEF level or quality sensor
- SCR system fault (P204F)
- Crystallised DEF injector
How to Fix It
- Top up with the correct AdBlue/DEF fluid
- Add enough to clear the low threshold (usually several litres)
- Wait for the system to re-read the level
- If it will not clear, scan the SCR system
- Have the DEF sensor or injector checked if faults persist
Related DTC Codes
| Code | Meaning |
|---|---|
P204F | Reductant System Performance The selective catalytic reduction (AdBlue/DEF) system is underperforming. |