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.
Medium severity. Can I keep driving?You can usually keep driving in the short term, but get it repaired soon: on many diesels, the warning eventually limits starting or engine power.
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)
Most likely causes
- Operation with high-sulfur fuel
- Desulfation regen strategy disabled or failed
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: hard
- It can trigger limp mode.
- It affects emissions.
What each character of P2C79 means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- C: Subsystem depends on the code range
- 79: Specific fault in that system
Frequently asked questions
Can I keep driving with code P2C79?
You can usually keep driving in the short term, but get it repaired soon: on many diesels, the warning eventually limits starting or engine power.
What causes code P2C79?
The most common causes are: operation with high-sulfur fuel; desulfation regen strategy disabled or failed.
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.