P2C79NOx Adsorber - Sulfur Limit Exceeded
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P2C79 says the sulfur load held in the NOx adsorber (lean NOx trap) has reached the limit the engine computer allows. Sulfur from fuel and oil occupies the storage sites more firmly than NOx, so capacity shrinks until a desulfation is run: rich phases with the trap above roughly 550 °C, as a Volkswagen patent explains. A Ford patent models the stored sulfur and starts this cleaning once a calibrated amount is reached, naming typical values between 0.1 and 0.5 g per litre of trap. CARB requires the trap and its desulfation hardware to be monitored. No manufacturer documents P2C79 publicly; it suggests the load stayed high, for instance because the trap never got hot enough on short trips. P2000/P2001 judge NOx efficiency, P21B4 overheating. NOx output rises and fuel use may grow.
- What you may notice
- Check engine light
- Higher fuel consumption from repeated rich regeneration attempts
- Occasional rotten-egg smell from the exhaust
- Raised NOx emissions, possible failure at an emissions test
- Likely causes
- LikelyDesulfation never completes because the trap stays too cool (short trips, idling)
- PossibleFuel with high sulfur content (outside EU/US ultra-low-sulfur grades)
- PossibleIncreased oil consumption carrying sulfur-bearing additives into the exhaust
- RareFaulty exhaust temperature or lambda signal that blocks or aborts the rich desulfation phases
- RareThermally aged trap whose sulfur can no longer be removed
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.