I have a 98 ITR (OBDII). I've read that if I want to run a testpipe I can just pull the O2 sensor from the cat and wrap it in tin foil (actually aluminium foil). I want to try this before I get rid of my cat, but I need to know what will happen if it doesn't work. Will I just get a CEL or will it throw my car into limp mode?

 

Just unplug the o2 and tape the other end of the connector either to the bottom of the car or just inside the hole that it feeds through so it is safe from harm.

You will get a CEL code.
You won't run in limp mode.

 

.....i've always wondered if tricking the 2ndary o2 sensor has any negative effects.

Does it affect fuel trim or anything? Mileage goes up or down? Or just emissions crap?

 

I think the second O2 is just there to ensure the cat is working. I noticed no ill effects with mine gone and the cel on.

 

You will get a CEL.

 

the foil worked for me, no cel in 5 months