Rotten egg smell and check engine light on my Grand Cherokee

Kennethashworth

So my 2018 Jeep Grand Cherokee with the 3.6 Pentastar started throwing a P0420 code a few weeks ago, and now I'm noticing this sulfur smell after driving on the highway. The car still runs okay but the fuel economy has dropped by maybe 15 percent. I took it to a muffler shop and they said the catalytic converter is probably failing, but they couldn't tell me if it's the cat itself or maybe a bad oxygen sensor causing it to run rich. I don't wanna spend two grand on a new converter if it's just a sensor or an exhaust leak. I'm trying to find a place that can do a proper backpressure test and look at live data from the O2 sensors before condemning the cat. I've been looking for Superior Catalytic Converter Abu Dhabi shops that actually diagnose instead of just quoting a replacement. Has anyone here had the P0420 code on the Pentastar and found it was just a bad upstream sensor or even an exhaust manifold leak? Also wondering if running a fuel additive cleaner could unclog a partially blocked cat or if that's just a waste of money. The car has 130k km on it and I really need to pass the next inspection. Any recommendations for an honest shop in Abu Dhabi would be lifesaving. Thanks a lot.

Gisellewannell

P0420 with sulfur smell and fuel economy drop together on a Pentastar at 130k km does point toward catalytic converter degradation, but a broken exhaust manifold bolt upstream is worth ruling out first since it can cause both the code and the rotten egg smell.

Gizellawarder

Live O2 sensor data during a highway drive cycle is the proper diagnostic step before condemning the cat. An upstream sensor reading correctly while the downstream sensor shows a healthy switching pattern means the cat is still functioning, which is something a muffler shop quoting a replacement won't bother checking.

Gladysewarenne

Backpressure test confirming restriction in the cat before replacement is exactly right. A partially melted converter substrate creates measurable backpressure that a live test reveals definitively rather than guessing from a fault code alone.

Glorianawarrington

Fuel additive cat cleaners are worth trying before spending on a replacement if the blockage is partial and the converter is not physically damaged. Results vary but the cost is low enough that it makes sense as a first step on a code that appeared recently rather than repeatedly.

Glorywashbourne

A bad upstream O2 sensor causing rich running that poisons the cat is a real sequence worth investigating. Replacing the sensor is significantly cheaper than a converter and sometimes resolves the P0420 entirely if the cat was not yet permanently damaged by the rich condition.