Need help diagnosing check engine code
 

I have a check engine light on and the code is P0420 on our 1999 4Runner:
"The PCM has determined that the catalyst system efficiency for bank 1 is below threshold for the current engine operating conditions. (bank 1 identifies the location of cylinder #1, while bank 2 identifies the cylinders on the opposite bank)
Am I correct in assuming the catalytic converter is the problem? Would the ISR and Deckplate mods I did, be the cause of the problem? Can I get rid of the catalytic converter and add a piece of pipe(no smog regulations here to worry about)? Also, the 4runner has an aftermarket exhaust on it I was told. I would assume it is from the cat back. Any thoughts?? :(

The cat probably is the culprit. It could be the rear O2 sensor. You can remove the cat but it will throw the same P0420 code unless you put an O2 simulator in it. Also check your exhaust system for leaks. A lot of folks have changed cats and sensors only to find an exhaust leak was ultimately the problem.

Thanks for the lead, I will jack up the 4runner and check for leaks first. BTW, who has it and how much would the O2 simulator be?

You can get them from several places. I got mine from URD. Cost was $59 as I recall. Works well.

Thanks for the tip, sure enough, I found a hole in the exhaust pipe right near the front O2 sensor. I welded it up last night, so will see what happens. Thanks again!! :bigok: :bigok: