O2 sensor removed-- no CE light
 

I went to the dealer this morning to get my rear O2 sensor replaced (the one back in the top of the catalytic converter) as I had the “Check Engine” light come on. While trying to get it out the threaded sleeve, which is welded to the cat, broke free and the dealer didn't have the welding capability to weld it back in position.

They told me to take it to the nearby muffler shop and have them weld the sleeve back into position to accept the new sensor and that they would reimburse me for the cost, since they broke it.

So I left the dealership with the threaded sleeve and the old sensor in a bag, and a nickel-sized hole in the cat where the sleeve was. It sure was loud and the reduced back pressure made the car run badly.

When I first started my car at the dealership to take it to the muffler shop, my CE light was off. After the sleeve was welded back on and the car restarted, the CE light was still off. I made a couple of more stops before going back to the dealer and my CE light never came back on (remember that I had the old O2 sensor in my car and the new one hadn’t been installed yet. There was still a re-welded sleeve with no sensor in it)

Here is the question:
If a bad O2 sensor would trigger the CE light, why would an O2 sensor that was removed or unplugged, or not in the system anywhere, cause the light not to come on? I thought that if you unplugged or cut the wires it would through a fault code.

John,

When I did my 4.11 trans swap, we shipped the wiring harness for my third O2 sensor to the buyer of my trans by accident. I drove my car for over a week w/o the 3rd sensor hooked up and no CE light came on...

I doubt removing the 3rd sensor would immediately trigger a CE light, but over time I'm sure a light would have come on.

-Chike

my car
 

I have removed the whole exhaust system from my car and replaced it with twin piping stainless system with two middle mufflers and two back mufflers... no check engine whatsoever... and fuel consumption is nice (around 17mpg)...

well first of all cuase the 3rd o2 sensor is worthless...

but i would think it would still throw a code. with it being OBDII and all.

really the first two o2 sensors are the ones that most affect the ECU, maybe the 3rd is only a redundancy factor? so if the first two work, the third one really isn't doing much? i dunno