PO420 code

[allred27]

hey guys, my check engine light came on last night, I checked it and got the "PO420 Catalyst efficiency below threshold"

what would it most likly be? the catalyst or the O2 sensor(s)? Or could it be something else?

I just did a tune up, new plugs, wires, cap, rotor, synthetic oil

it's a '96, Tacoma 4x4, 2.7, 183K miles

Thanks

[ryanyoshi]

I just recently had that problem. For me it was due to an installation of a aftermarket catalytic converter since somebody stole my stock one. I'm pretty sure that it is your cat. and not your sensor. It's expensive to replace with a factory one. It'll be less than half the price to get an aftermarket cat. and an O2 simulator from URDUSA.com. Thats what I did and now my truck runs perfectly with not engine light. Hople this helps.

[tacotoe]

I had the same code (s) several months ago. I first replaced the front O2 (AFRM) sensor but the light came back on, then I bought some MAF cleaner, along with a can of TB cleaner and used them, then got a3?? code which was a TPS code (truck went into limp mode) then replaced the rear O2 sensor along with the TPS and the Light has been off every since. Tomorrow afternoon I will try to find pictures to post of the O2 sensor and TPS replacement but no guarantees as that particular camera`s lcd went out, I think I have them downloaded though.

[allred27]

Finally had some time to work on my truck. I wanted to look at the cat before I ordered a new one, so the owner before me just welded a new one on, it's not even the correct size, the cat's ends are 1/4" bigger then the exhaust pips, they just filled in the difference as they were welding.
So it looks like I only have to options;
1. cut off the cat and weld a new one back on
2. replace the exhaust system
So if I put a new exhaust system on, which header? And exhaust system should I get? I'm looking for power and sound.
Thanks