What it means
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.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
A NOx adsorber catalyst stores nitrogen oxides from the exhaust and periodically needs a desulfation regeneration to clear accumulated sulfur. The engine control module estimates sulfur loading and sets this code when the calculated load exceeds its limit. The catalyst may then remove NOx less effectively, potentially triggering emissions warnings or an inducement countdown.
Common causes
Most likely first.
- Operation with high-sulfur fuel
- Desulfation regen strategy disabled or failed
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)
How to diagnose it
- Read freeze-frame data and the NOx aftertreatment status to confirm the sulfur-load fault and note any active inducement or no-start countdown.
- Check the vehicle's fuel history and applicable fuel specification for possible high-sulfur fuel exposure.
- Use a capable scan tool to check whether desulfation regeneration is enabled, requested, completed, or inhibited, and record any related faults.
- Diagnose faults that could inhibit regeneration, including relevant exhaust temperature, NOx sensor, and aftertreatment codes.
- If the system permits it, carry out the manufacturer's desulfation procedure and verify sulfur-load and NOx readings afterward.
Common fixes
- Use fuel that meets the vehicle manufacturer's required sulfur specification.
- Repair the fault or operating condition that is preventing desulfation regeneration.
- Perform the manufacturer's desulfation regeneration procedure when system conditions allow.
- Replace the NOx adsorber catalyst only if testing shows it remains ineffective after correct regeneration.
Can I keep driving?
Follow any displayed countdown and warning instructions; ignoring the fault can lead to reduced power or a no-start restriction, and the vehicle may fail an emissions inspection. Avoid assuming a warning will clear on its own, and arrange diagnosis promptly.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.