i just bought a 99 civic for very cheap and it has the cel on. codes are p0420 and p0133 i have read hundreds of threads on it. when i first bought the car it only had p0133 so i replaced the o2 sensor. a bit later on the p0420 along with p0133 also popped up. i know most threads said bad cat.
i have a feeling the person that worked on the car before me wasnt too smart, i seen a few rigged wires. and i seen both o2 sensors have the same plug. how can i tell if its hooked up right? i just want to rule this out. anyone have a wiring diagram?
also the reason i figured it was the primary o2 was because all the wires were stripped back and touching each other near the sensor. could this have shorted something that i should check?
the car runs good other than a tiny surge on throttle, it only does it for a split second. and not every time i drive it. any help would be greatly appreciated.

 

I believe on the primary wiring on the harness side there should be a white wire, on the wiring side of the secondary there should be a white/red wire. Try that, fix your wiring and check your underhood fuse box for any blown fuses. Reset the ECU and see if it comes back.

 

Thanks, ill check those when i get home

 

If you have a Haynes manual, they have wiring diagrams for everything electrical in your car in the very back. If you don't already have one, I would suggest getting one. Those wiring diagrams have saved me a lot of trouble and headaches.

 

just an update. the problem was the o2 sensors hooked up backwards. i am surprised it ran so well with them hooked up wrong. i have driven over 300 miles without the cel coming on.