Q: Check engine light is on. 04 Pathfinder. Quick check at Autozone and clerk said possible vacuum leak, o2 sensor, or catalytic conv

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The check engine light is on. Car runs very well but gets poor mileage. Autozone put a code check on it and said it was either a vacuum leak, an o2 sensor, or a catalytic conv. Your opinion?

My car has 11640 miles.
My car has an automatic transmission.

Hi there. Like any other professional mechanic would ask, my first question is what specific OBD-II trouble code was pulled and what symptoms is the vehicle experiencing? If the engine idle is high or extremely low, this would be a typical sign of a vacuum leak. If the car had issues with acceleration or the engine was stumbling during idle, then O2 sensors or a bad catalytic converter would be suspects as well. The problem with the code readers that most auto parts stores use is that they are simply that - code readers. They are unable to download all stored error codes from the ECU; which is only possible from professional digital scanner used by certified mechanics. This tends to tell the entire story about any mechanical or electrical fault that triggers the check engine light. The best way to begin any diagnosis is to have a professional mobile mechanic come to your location and complete a check engine light inspection, which will allow them to download all stored codes and determine exactly what’s triggering the light; so the right repairs can be made.

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