نشتی اگزوز قبل از جاذب

A leak in the exhaust upstream of a NOx adsorber, admitting outside air into the stream it treats. Exhaust flow is pulsed, so a leak draws air in during the low-pressure part of each pulse even though the average pressure is positive.

Extra oxygen defeats the trap's chemistry. The adsorber stores oxides of nitrogen under lean conditions and releases them under rich ones, and unmetered air stops the rich excursion ever arriving at the catalyst — so purge cycles fail and efficiency codes follow, with a trap in good condition. Listen for a tick that follows engine speed and is loudest cold, before the metal expands and closes the crack. Check for a leak before condemning the adsorber, which is among the most expensive parts on the vehicle.