AdBlue faults • SCR diagnostics • 2026
AdBlue Fault Codes Explained
P20EE, P204F, P20E8 & More
Warning light on.
No-start countdown ticking.
This guide explains what the fault codes mean, what usually causes them, and what actually fixes them.
Mobile across Leicestershire • Mon–Sun 09:00–20:00
Modern diesel vehicles rely on the AdBlue SCR system to control emissions. When something drifts out of range, the ECU logs a fault code.
Some codes are warnings.
Others start a countdown that ends in a no-start.
Most common AdBlue fault codes
| Code | What it usually means | Risk level |
|---|---|---|
| P20EE | SCR efficiency low, often linked to NOx sensor or dosing issues | High – countdown likely |
| P204F | Overall AdBlue system performance fault | Critical – no-start risk |
| P20E8 | AdBlue dosing control malfunction | High |
| P2BAE | NOx emissions exceeded limits | High |
| P207F | AdBlue quality or concentration issue | Medium–High |
Why AdBlue fault codes trigger no-start countdowns
The ECU does not care which part failed.
It only checks emissions compliance.
- Repeated faults escalate severity
- SCR efficiency drops below limits
- A countdown starts and cannot be ignored
If you are already in countdown, see how to clear a no-start countdown without the dealer.
Key AdBlue fault codes explained
P20EE – SCR efficiency below threshold
Usually linked to NOx sensor readings, dosing issues, or long-term unresolved faults.
P204F – Reductant system performance
Often caused by pump pressure problems, injector blockages, or contaminated AdBlue.
P20E8 – Dosing control fault
Common on higher-mileage vans and frequently leads to countdown activation.
P207F / P20BA – AdBlue quality faults
Triggered by diluted, old, or contaminated AdBlue, or sensor mis-reading.
P2BAE / P2BAF – NOx exceeded limits
Usually appears alongside other unresolved AdBlue or NOx faults.
AdBlue fault codes – FAQs
Can I keep driving with an AdBlue fault code?
Some faults allow limited driving. Many escalate into a no-start countdown.
Will topping up AdBlue clear fault codes?
No. Faults require diagnosis and a reset after repairs.
Why does the countdown stay after fixing parts?
The ECU must confirm stable readings before allowing a reset.
Is it cheaper to repair or delete the AdBlue system?
It depends on age, mileage, and repeated failures.
Can AdBlue faults affect MOT results?
Yes. Active warnings and no-start conditions can cause MOT failure.
Stuck with an AdBlue fault code?
We diagnose AdBlue, NOx, and SCR faults properly and offer mobile solutions across Leicestershire.
Call 07349 821 999
