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Ok, so I am trying to help my friend with this DTC p0420. For those who don’t know it’s a catalyst efficiency threshold issue. Well, after looking it over and being the car had almost 90,000 miles we put a new cat in it. The code came back. We tried another after returning the first on warranty. Same shitty code. Tried it one more time. Again, the code came back. O2 sensors were also replaced. Still the same damn code. Anyone have any experience with this code? Possibly on this model car? Please HELP!
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They were aftermarket. He didn’t have the money for the GM cat. And we knew beforehand that it might not last as long but the light came back on immediately.
the code p0420 happens with these after market cats. due to there high flow capabilities. the 02 sensor
can’t pick up the flow to read it.C8-) so the computer throws the code.Quoted From college man:
the code p0420 happens with these after market cats. due to there high flow capabilities. the 02 sensor
can’t pick up the flow to read it.C8-) so the computer throws the code.So basically the only way to get rid of the code is to use a GM cat?
All I’m saying is that when people post with this code and they have installed an aftermarket cat. The problem
was not there when they had the OE cat.C8-)Quoted From college man:
All I’m saying is that when people post with this code and they have installed an aftermarket cat. The problem
was not there when they had the OE cat.C8-)No it was there. That was why we replaced the cat in the first place. The code came before the first aftermarket cat was installed.
Perhaps a different brand before you go for a GM unit. Just to be sure you do have a cat issue if you can get your hands on a scan tool that reads live data and observe the O2 sensors front and back after the engine warms up. The front O2 should switch back and forth across .5v fairly quickly, the rear O2 however should stay pretty steady near .5v and not move around all that much, this is what you should see if the catalytic converter is doing it’s job. If you see any abnormalities in the readings you might check the wiring of the O2 sensors since you have already replaced the sensors. If everything is good there and you’re still getting that code you might find a different brand of cat or go with an OE unit.
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