Quote:
Originally Posted by hayden55
Cat is probably good its your oxygen sensor fouling out.
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That can be tested, but I have a feeling it's not the sensor.
There are two sensors, one before and one after the cat. The one before has to constantly vary it's signal because that's what O2 sensors do after an engine as it gets hit with pulses of unburnt fuel and air, otherwise it'll set an O2 sensor code.
The second one has to stay flat, since after the cat the pulses of oxygen and unburnt fuel are now catalyzed and don't vary as much. If the second sensor varies like the first then it will set the failed catalyst code. It's kind of hard, or maybe even impossible, to set such a code with a bad O2 sensor.