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Discussion Starter #1
Heads up.
I have a 2013 Jeep Compass Limited 4WD.
I got a check engine light popup. I checked the code and it said P0420 (Catalyst system efficiency). I figured it was not a big deal. I reset it and drove around for a few weeks with no issues. Then it started happening. I would get a check engine light, i would check for a code and no code was present. The light would stay on for a day or two, then it would go off. Two or three days later it would come back on. Again no code was present. Then again the check engine light would clear itself.

This went on for a month. I finally gave up and had a mechanic shop look at it. They test drove the car and both O2 sensors functioned properly. The issue was not bad sensor. The shop recommended a new catalytic convertor.
When the old catalytic convertor was removed the issue was discovered.

A weld had failed between the catalytic convertor and the exhaust manifold. As the system was cool, it would allow an exhaust leak. when the metal got hot the metal would expand closing the gap and the system would test normal clearing the check engine light. The flexing caused by the temperature changes also started crack formations in the exhaust manifold itself.
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