So I have removed the stock rear O2 sensor, and repalced it with a wideband. I found the thread on how to make the changes in ecuflash and add a resistor in the harness to turn off the CEL. My question is what is the impact on the car right now? With no signal from the rear O2 does the ecu add/subract fuel or anything to do with timing. I don't care if the CEL is on the bulb burned out anyway, I just check the DTC's every month or so, but I want to make sure it is not harming the car in anyway. Any input, thoughts or info would be great, thanks in advance.

 

hmm, well this should not be an issue because the rear o2 sensor is used to make sure the cat is working correctly. There is actually an option in the tephra mod map that allows the emulation of what the front o2 sensor is reading to the rear o2 sensor, so one would think that the rear o2 sensors input in terms of ecu feedback is not important. Hope this helps!

 

Any input helps, thank you. I just want to make sure I'm not hurting the car, and/or impacting the tune at all. It there any reason to make any changes other than turning off the CEL?

 

None that i can think of. If you have any doubt , just weld a bung for the wideband o2 sensor on the downpipe 4 inches away from the cat. This way you get to keep all three sensors and no cels!

 

And put the o2 sensor as close to 12 oclock as you can to prevent moisture away from the sensor.

 

I haven't looked through the code, but I beleive the rear O2 actually is used in some of the O2 feedback stuff to control fuel.

 

I know the front O2 really controls the fuel, but if the rear is monitoring the cat and there is no signal I would think the ecu makes some type of adjustment. Anyone else ever wondered this? Thanks for the input so far guys!

 

03whitegsr is right....you need it for fuel trims.

 

Why would the post cat o2 sensor be the one used for fuel trims?? Am I completely missing something?? I have been getting the p0420 about every two weeks or so. If this is affecting my fuel trim then I need to figure something out! Any advice would be good!
By the way I have a 3" Turbo back installed w/ high flow cat. Thanks guys!!

 

wouldn’t surprise me at all it has an effect on a Mitsubishi.... i know for a fact that on my 04 STI when you disconnect the rear O2 the car will run about 1.0 AFR richer. best explanation i have been able to find is that the ECU uses the rear O2 to check the cat efficiency and fine tunes the fuel to keep the cat in its most efficient operating range.

 

Or you could read all of the other threads that you got that information from....

It is only used to check catalytic efficiency, but disabling one of the periphery bits (that was originally thought to be a solution, and later found to not be) will cause the trims to stop adjusting.