Here is a good example where Pre-Cat O2 sensors were lazy, no codes were every triggered and there may not have been any obvious problems. I do not recall all the details and exactly what we were attempting to resolve, but I think this graph is very self explanatory even to a novice person.

The Pre-cat O2 sensors were lazy, probably high mileage units that should have been replaced long before they were, but we were able to get the data, determine the Pre-cat O2 sensors were lazy and they get after data so we were able to compare a before and after case.

Attached Images

 

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2008 4.8i Black with Tabacco. Black Y-spoke wheels and shadowline trim.