Well, its finally time for my inspection, and I'm pulling an O2 code from my headers/cat removal.

I have a set of O2 simulators to install. Does anyone know which wires do what on the rear sensors?

I have it down to 2 options, but don't know enough about reading the electrical symbols on the Haynes wiring diagram to get the rest of the way. Ideally, I'd like to install them inside the cab, near the ECU.

Thanks in advance.

All four of the O2 sensors connect on the top of the right side valve cover. I would have to check on which one is which for sure, but I do believe that the rear pair, there are four, go to the rear, heated O2 sensors. These are the important ones because they really sense you fuel mixture.

I'm not sure it's a good idea to remove those, however, they do more than just emissions. They adjust your engine for best efficiency and air/fuel mixture.

Here are the O2 cat monitor wiring Diagrams
with the ECM pin #s and wire colors.
this is for bank one


and this is for bank two



Hope this helps

Dagger - right now there are no cats between the up stream and downstream sensors, so are the rear sensor actually performing the way it was designed to in the first place? I would think that the rear O2 would be reading rich and leaning out the mix? That's how I understand it at least.

Thanks 4Runner, that is what I was looking for, much easier to follow than the overall schematic in the manual.

If I'm reading this correctly, the signals to the computer are the R/B and R/Y, correct?

The rear O2s don't control fuel mixure they are for monitoring the cats only.
right now they are responding the same as the front O2s causing a code for the cats failure. p0420 or p0430.
so when the simularors are installed they cause a flat voltage signal to the Ecm saying that the cats are working.
The computer looks at the front O2s for mixture control
and the rear O2s for the cats.
the fronts swing rapidly adjusting to fuel mixer
the rear O2s swing very slowly on accel and decel
they should stay pretty constant most of the time
that is how the computer knows when the cats have failed because the rears start acting like the fronts.
not sure on the exact wires that you need because of the simulators that you may have.