well i tried the mod to eliminate my 02 after the cat. using a 12 ohm resistor and a 1 micro farad cap and a 1 megaohm resistor. i disconnected the rear o2 from its harness and wired it as i was told and now i am throwing a Cel 21. upstream o2 sensor failure. why would this be. i didnt even mess with that one. that is the only cel i have. and the car runs worse. any ideas what i did wrong? also my o2 has 4 wires. two white. one grey and one black. and the harness it connects to has a thick black w/red , a black w/green, a black with grey squares on it and a white with green . what is what? which are heaters and such? im pretty sure the white w/green is signal out.

Sounds like you put a resistor on the heater wire instead of the signal wire, and since both O2's probably share the same 12v source, youre affecting the front O2's power.

Remove the mod, hook it back up as stock, and see if it works again.

If it does, redo the rear o2 mod. correctly.

ok that may be it. but i still dont know what the colors are as far as where they go to . i re hook it back to factory and its fine. ill re attempt after someone tells me what the wires are

black w/red = ?
white/green = signal output i think
black w/green= ?
black w/ grey boxes = ?

anyone know. the black with red is thicker than the rest and it shows + 12V when car is on. is this heater wire?

Originally posted by 97grnRS
ok that may be it. but i still dont know what the colors are as far as where they go to . i re hook it back to factory and its fine. ill re attempt after someone tells me what the wires are black w/red = ? white/green = signal output i think black w/green= ? black w/ grey boxes = ? anyone know. the black with red is thicker than the rest and it shows + 12V when car is on. is this heater wire?

by looking at the schematic diagrams, it's sort of hard to decifer, but I believe its like this..

black/red= heater positive
black/green=heater negative
white/green=signal out
black= sensor ground

I've got just a 1 megaohm resistor inline with the black wire at the rear o2, and never got a CEL yet. The schmetics show that BOTH front and rear o2's share that black ground wire, so I would only tap into that right by the rear o2 sensor...not sure exactly where it branches off to feed the front o2..