Thread: p0420 engine code

doesnt hurt to reset your DTC codes

What kind of cat?

If it was a cheapy highflow cat, its still going to set the code because it flows too well for the stock specs.

It's weird I gutted my cat a few weeks ago... still no code.. lol

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Originally Posted by Fivefingerdeathpunch

What kind of cat?

If it was a cheapy highflow cat, its still going to set the code because it flows too well for the stock specs.

Exactly!!!!!!!!!!!!!!!! ^^^^^^^^^

Lots of problems come from "Generic or Universal cat's"

Black tape works great to get rid of the code!!

Originally Posted by gearjammer79

Hey guys I have an o2 grand prix that I cant seem to get rid of this p0420 engine code.. I have repalced the cat, plugs, wires, coil pack, both front and rear o2 sensors, coolant temp sensor.. I have even repalced gas cap as was told that could have something to do with it as well and still no solution.. has anyone else had this problem or can someone tell me what I can do to cure it....

i had the exact same problem. midas put on an aftermarket cat and the code still came up. found out that if you use a non-gm cat that this code frequently keeps popping up. i bought an o2 simulator and un-hooked the rear o2 sensor and the code went away..sort of. if you do a scan of the computer it'll show a o2 heater as pending because the simulator doesn't have the heater circuit. but the o2 simulator will keep the SES light from coming on.