This may be complete coincidence. Had a CEL for quite a while, might have been since last oil change. Intermittent initially but has stayed on for last several thousand miles. Catalytic inefficiency code. Changed my oil/filter on Sunday. Noticed I was maybe a little under a quart overfilled, my mistake. I always pour my used oil back into oil 5L oil bottle, and this time I overflowed the container with some left in topside oil extractor. Oops. But, driven a couple hundred miles since and CEL is nowhere to be found. I have an AWE downpipe with hjs cat. Even bought j spacer and new o2 sensor to install before last oil change. Could just a quart or little under a quart overfill cause some fouling of cat/o2 sensor?
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