Ok so I picked up a 05' EP3 a couple months back. Finally had time to fix the CEL it had. Pretty simple fix secondary o2, or so I thought.
After replacing the o2 sensor and doing a reset. The CEL went away for about an hour maybe 2. Thinking it was possibly a faulty new sensor I returned it and got another. No biggie just a lil extra time...Same thing happened again.Its been a couple weeks now (since geting frustrated with it and just letting it be )and the CEL will periodically turn off then come back any where from an hour to as long as a couple days. This time I noticed that my auto window switch doesn't work when the CEL turned off. Then after the CEL came back and only after a complete cold start would the auto window work again. An yes the CEL would still be there ....Since noticing this it has happened at least 5 or more times. Every time the exact same way. An when the CEL is on it reads for 2nd o2 and when off nothing (like it should).

The only thing I can come up with is the multiplexor is causing it. But before spending a bunch of money on it. I would like some other opinions.