P2C79
NOx Adsorber - Sulfur Limit Exceeded
The ECM detects that the cumulative sulfur load on the NOx adsorber catalyst exceeds the calibrated threshold. Desulfation regeneration is required to restore catalyst function.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
Common causes
Ordered by how often each turns out to be the cause.
- Operation with high-sulfur fuelCommon
- Desulfation regen strategy disabled or failedPossible
Parts involved
- NOX Adsorber Catalyst
P2C79 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.