[Z06] Check engine light
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
DTC P0420 or P0430 = Catalyst System Low Efficiency.
P0420 TWC System Low Efficiency Bank 1
Bank 1 is the driver's side.
Try the search function ... probably some threads on this DTC. Search for "P0430".
P0420 TWC System Low Efficiency Bank 1
Bank 1 is the driver's side.
Try the search function ... probably some threads on this DTC. Search for "P0430".
Instructor
Joined: Aug 2007
Posts: 185
Likes: 2
From: Bay City Texas
My understanding is that if you have high flow cats typical when installing headers, the rear O2 sensors don't heat up very quickly. Since the computer compares front to rear to determine cat performance, it will then throw the code because the two don't compare correctly (you can look up the reason, but I've seen two different explanations on what the computer is looking for. I don't think it really matters what as long as you understand that they are compared).
So the solution appears to be to delete rear O2 sensors which should include no mil for P0420/P0430.
If the rear O2 sensors have already been deleted, then sounds like setting P0420/P0430 to no mil was skipped.
Instructor
Joined: Aug 2007
Posts: 185
Likes: 2
From: Bay City Texas
I have also heard that the car may click along just fine and then a high cross wind might cool the rear O2 sensor and throw the code. Or maybe you drive on a wet road and that cools the rear O2 sensors.
Of course, you might just have O2 sensors going bad.
Since installing headers, I haven't had rear O2 sensors so have no experience with the problem. But I would think you should be getting other codes if you have a bad sensor.
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