O2 Sensor Fail(s)
 

A while back I gutted both cats on my '99 Cali car because they had melted on track and clogged up. I ended up with a P0420 CEL (surprise). I left it alone for a while, but now I need to get the CEL to go away (totally not because I need to pass emissions).

I wired in an O2 simulator on the rear sensor, but for a while it didn't look like it was working.... until I found the O2 sensor harness unhooked in the engine bay. :facepalm: Now the car is throwing a P1135 code, for the upstream sensor.

So, couple of questions: should I replace the front O2 sensor? Or is the problem more likely something to do with the simulator not playing nice with the computer?

Also, when I gutted the cats, I also installed an 01+ manifold. I bought a new upstream sensor for a 2001 from O'Reilly, but it is not long enough to reach all the way to the front of the cam cover. So, is there an OEM O2 sensor with long enough wiring to go from the 2001+ sensor bung to the 99 Cali-spec harness location? Can I use a downstream sensor instead of an upstream sensor?

My '97 is a Cali car and I had a cel pop up for cat under threshold or bad secondary O2. I wired a simulator in the secondary hole and ran a test pipe. No issues. I would lengthen the wires for the primary and put it the right spot. Just splice the old O2 wires to the new O2. I don't know about it fitting the harness in the secondary. To my knowledge the only thing the secondary (post cat) one does is check to make sure the cat works properly. I don't beleive if you plugged the primary in there and left a plug in the header the ecu would know what to do with it. All it would know is a sensor is missing and/or the cat doesn't work.

Thanks, I had the feeling that was the case on the secondary. O'Reilly had another upstream that was listed as an "alternate fit" for a 2001, which was about 4" longer than the first one I bought. Turns out that was just enough. I ran the car for a few minutes in the garage and no code. I will test it out tomorrow, but I'm cautiously optimistic...

Well it worked. The O2 simulator seems to be doing its thing. I've put about 30 miles on it with no code...

The computer stores those codes for a period of time, right? You should still have them checked out and or cleared before going to not get it inspected...