Fault-Code Library · AdBlue / SCR
P2BA9: NOx exceedance due to insufficient reductant quality
The SCR system calculates excessive NOx emissions associated with reductant quality or dosing performance.
Common symptoms
- •AdBlue warning
- •Restart countdown
- •Engine warning light
- •Emissions-test failure
Likely causes
- •Incorrect or contaminated AdBlue
- •Dosing fault
- •Biased NOx sensor
- •SCR catalyst or temperature issue
First checks
- •Verify fluid quality and concentration
- •Check dosing quantity
- •Compare upstream and downstream NOx data
Important
Do not replace the SCR catalyst until fluid, dosing, sensors, leaks, and temperature conditions have been proven.
A fault code identifies a detected condition, not a failed part. Confirm manufacturer-specific subcodes and live data.
Related research
Continue your research
Move from brand context to exact model, powertrain, fault-code, and buying-checklist evidence.
Buyer help
Request a used-car risk review
Send us the model, year, engine and mileage. We'll help identify the main risks before you buy.
Known engine and gearbox weak points.
Fault codes and symptoms to verify.
Inspection questions before negotiation.
This is buyer guidance, not a remote mechanical inspection or a guarantee. Always verify the car in person with diagnostics and service records.