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1998 Pontiac Transport Engine code P0420

05-22-2007, 09:47 PM
The check engine light intermittantly comes on. Only code showing is P0420 which is catalytic efficiency. Replaced catalytic converter six months ago after this code started showing up and it stopped for 6 months. Now its back. Car has 160K miles on it. suspect it is time to replace the aft O2 sensor (behind the converter) but wanted some other opinions.

Also, what about removing the converter altogether. We live in a state that has no smog check. Will removal of the converter cause the catalytic efficiency test to always fail?

All opinions welcome.


05-23-2007, 08:50 AM
Yes it will keep the lite on , plus removal is a Federal offense. Do a site search for the code, lots of info. A good test for cat operation is to get the engine hot, using an infrared thermometer check inlet vs outlet temps, outlet should be about 100 degrees higher.

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