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Old 03-04-2009, 11:20 AM   #2 (permalink)
Daox
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It really shouldn't effect mileage. The front o2 sensor is mainly the only one the engine uses to maintain correct air/fuel ratios. The rear one mostly there to ensure the CAT is doing its job. Ironically, the rear O2 sensor usually goes bad before the CAT.

My guess is the O2 sensor went bad. I would take it in to get looked at since you have the warranty.
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