P2BA6
NOx Exceedance - SCR NOx Catalyst Performance
NOx emissions are above the legal threshold and the ECU isolates the cause to the SCR NOx catalyst. Conversion efficiency is degraded — aged substrate, sulphur poisoning, or thermal damage.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
Common causes
Ordered by how often each turns out to be the cause.
- SCR catalyst substrate aged or contaminatedCommon
- Thermal damage from prior over-temperature eventPossible
Parts involved
- SCR Catalyst
- Reductant Dosing Unit
P2BA6 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.