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Diagnostic Code P0420


JeffL.
01-15-2004, 04:35 PM
My Check Engine light came on just a few days ago on my 2000 Ram Air. I stopped by AutoZone and they checked it and told me it was a P0420 Code which is defined as "Catalyst System,Bank1 Efficiency Below Threshold"

Their suggestion was to replace the O2 sensor on the output side of the converter (driver's side of the car). I've never done this and it is in an awkward place, but I don't think it would be that hard. However, that was their guess, so I'm a little hesitant to do that. I also checked the exhaust near the converter and I didn't see any holes or leaks that might fool the O2 sensor.

Has anyone had this code? Or has anyone replaced on O2 sensor on these vehicles? I'm pretty good with electrical stuff and if anyone knows how to test it, please let me know that as well.

Thanks,
Jeff

95fbodyunder3k
01-25-2004, 11:09 PM
changeing the o2 might work if it isnt in a tight spot all u need is a big box end wrench just disscionect the battery first but it also could be a problem with the cat its self how to check it can be checked with a volt meter use millivolts make sure u probe the signal wire its usualy black start the engine let it idle let it warm up should jump from 100mv to 900mv watch closely write down the high, low readings over one minute it should average around 500mv another test is to take a vacume line and the voltage should lower to 200mv
BE SURE U TEST IT AT THE CORECT WIRE THERE SHOULD BE A GROUND A SENSOR OUT PUT AND A HOT WIRE ;)

JoeJoe231455
01-29-2004, 05:59 PM
My Check Engine light came on just a few days ago on my 2000 Ram Air. I stopped by AutoZone and they checked it and told me it was a P0420 Code which is defined as "Catalyst System,Bank1 Efficiency Below Threshold"

Their suggestion was to replace the O2 sensor on the output side of the converter (driver's side of the car). I've never done this and it is in an awkward place, but I don't think it would be that hard. However, that was their guess, so I'm a little hesitant to do that. I also checked the exhaust near the converter and I didn't see any holes or leaks that might fool the O2 sensor.

Has anyone had this code? Or has anyone replaced on O2 sensor on these vehicles? I'm pretty good with electrical stuff and if anyone knows how to test it, please let me know that as well.

Thanks,
Jeff

Have you modified your exhaust system at all? The code your throwing is in fact the "cat sniffer o2 sensor" mounted after the catalytic converter. I threw it non stop on my 01 gtp after I modified the downpipe. Too little backpressure makes that sensor unhappy for some reason... It can be thrown if you have removed or gutted your cat, if your cat is going bad, or if you add a larger downpipe, or the last option, your 02 sensor has gone bad, or the wiring to it is damaged.

As previously mentioned I'd have your sensor tested before replacing it. They are a fair chunk of change to replace iirc. Keep in mind if your cat or cats (not sure of the LS1 setup) have gone bad you can have them replaced at no cost at any gm dealer for up to 100k miles under federal law.

JeffL.
01-30-2004, 04:56 PM
Well, I found a friend of a friend who has been looking at it the last few days. He's GM certified and does a little work on the side. He had a whole lot of diagnostics connected to it and showed me the voltages coming back from the sensors. It is showing that the O2 sensor is a little slower on the left than on the right when it comes to responding. We took a chance and replaced the O2 sensor hoping it is that and not the cat.

It's all stock exhaust at this point, I haven't modified it (even though I probably will one day, it could be a little louder!).

Is that really true that they will replace the cat at no charge if it is found bad w/less than a 100K? Mine is just shy of 40K.

JoeJoe231455
01-30-2004, 07:24 PM
Yes it is true...federal law..

JeffL.
01-30-2004, 08:11 PM
That is some GREAT information!!!!

Jeff

JeffL.
02-02-2004, 03:59 PM
Well, the SES light didn't show up for about 5 days and 120 miles. That's the longest it has ever lasted without coming on. I ususally don't drive that far, but I wanted to make sure that it wouldn't come back on. However this morning it did.

I guess I will take it to the dealer. I just hope they don't find something silly to charge me for or try to work their way out of it.

Also, I did find out that they have to change it if it is bad UNLESS it has been abused or tampered with.

Jeff

tyranny
02-23-2004, 09:07 PM
GM's policy on catalytic converter warranty is 8yr./80,000mi.

Flatrater
02-23-2004, 09:38 PM
Federal LAW is 8 years 80,000 miles. Now GM has been having a problem with false codes on their carlines and the fix is to reprogram the computer. I'm not saying that is your problem but let the dealer look into it.

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