I just had to replace the downpipe on my gti and now it keeps making my check engine light turn on with a code p0420. Is there something like a cat sim or some way to trick the o2 sensors? i also have a mustang and they make a wire that simulates the cats and works perfect. . . . just wondering and hoping that there is something like that for this car. thanks so much.
correct. a dirty MAF sensor can cause it to happen as well. i have the same code on my gti. it is because i have a 3in turbo back exhaust with a high flow cat. so my post cat o2 sensor thinks there is something wrong with the cat. if i add the o2 spacer it should take care of it. i have cleaned the o2 sensor before and it fixed it for a few hundred miles. i did see or hear about o2 simulators but not sure if they would work on a vw.
Thankscso much all for the quick replies. I thought that maybe the sensors went bad but it didn't seem to go off until I changed this pipe. It is an aftermarket downpipe and it is a bit larger than the stock one so I'm afraid to waste money on new o2 sensors when mine are ok. I think I am going to give the o2 spacers a shot. Thanks so much all
yeah your o2 sensors are probably fine. because of the bigger downpipe the o2 sensor is reading more exhaust so its tripping the light. really o2 spacer is your only hope. your in the same boat as i am. i just could care less about the light. eventually ill order a spacer.
well jljb, if you haven't notied but volkswagen is not exactly the cheapest car out there. The stock replacement pipe for this car is about 1000$. I am not ready to spend that much for a pipe for a commuter car. So when i see a pipe for $85.... Ill take it. Thanks for your concern.
jim64123 I just would have thought that a replacement would be the right size I didn't mean to sound crabby.
I just meant you wouldn't put the wrong size spark plugs in it or the wrong size tires as that could cause a problem?!
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