Help with Code P0420
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Junior User
Joined: Sep 2003
Posts: 53
Likes: 0
Help with Code P0420
I have a 1996 5.8 bronco and the guys at autozone said my code was P0420 which equals Catalyst System Efficiency Below Limit, Bank No. 1. what the heck does that mean...i have replaced the rear o2 sensor(behind cats). he told me that my cats were shot?? if i need to replace an o2 sensor in the front, which one or is this a bigger problem. thanks alot for the help....
Freshman User
Joined: Oct 2004
Posts: 35
Likes: 0
From: Reno,NV
What is happening is the front o2 sensor is "seeing" a certain amount of richness and the rear sensor isn't seeing it clean up as much as it should be. Ether the front o2 sensor is faulty or your cat isn't doing the job it should. I would find out if there was a way to test the front sensor to see if it was good.
Freshman User
Joined: Oct 2004
Posts: 35
Likes: 0
From: Reno,NV
I know there is a way to test them I just don't know how. I know they are supposed to "swing" their voltage from lower to higher telling the FI to add or reduce the fuel input. I just don't know what the voltage is supposed to be or what wires to hooh up to. I'm pretty sure 2 of the wires are for the O2 heater and the other 2 are for the monitoring. Not sure which is which. Try calling a local shop and asking a service writer about it. Also try calling your local University or Community colledge auto programs. The teachers are usually very willing to help out. I know here they are.
Hotshot
Joined: Jul 2002
Posts: 14,285
Likes: 12
From: Bend,OR
if you must replace on o2 sensor then the rest are going to be bad as well. your system has 3 total. so replace the other 2 an see where your at. if you still have the code then your cat is shot and will need replaceing. which would be a great time to have the exhaut upgraded and headers installed.
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