97 deville p420 code
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Northstar Engines and System Technical Discussion Discussion, 97 deville p420 code in Cadillac Engine Technical Discussion; I just bought this 97 deville cheap however driving it home i get service engine with a pcm code p420 ...
  1. #1
    fullserviceman is offline Cadillac Owners Fanatic
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    Exclamation 97 deville p420 code

    I just bought this 97 deville cheap however driving it home i get service engine with a pcm code p420 what is this? I know the wires were replaced due to a misfire however at speeds over 55mph i get a vibration in the front seems alot like a misfire..... Any Ideas????

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    up2ng's Avatar
    up2ng is offline Cadillac Owners Member
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    Re: 97 deville p420 code

    Quote Originally Posted by fullserviceman
    I just bought this 97 deville cheap however driving it home i get service engine with a pcm code p420 what is this? I know the wires were replaced due to a misfire however at speeds over 55mph i get a vibration in the front seems alot like a misfire..... Any Ideas????
    It sounds like you catalytic converter is shot (p0420 - low cat efficiency)
    but you need to find out why before you change it.

    How many miles ?

  4. #3
    mcowden is offline Cadillac Owners Connoisseur
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    Re: 97 deville p420 code

    It could be the catalytic converter. It could be the pre- or post-cat O2 sensor failing, but that should set another code, so it's likely the cat. It's possible they had a bad O2 sensor for a long time and never changed it so it eventually burned up the cat, or bad gas can do it over time, there are lots of possibilities here. If there are no other codes, consider changing out the cat. A Walker #15818 direct-fit converter is about $162 from www.rockauto.com and then shipping and installation charges on top of that if you don't do it yourself.

    The vibration above 55 might just be a tire out of balance. If there's a misfire, it should set a P0300 code. Let us know what you do...
    Mike

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    fullserviceman is offline Cadillac Owners Fanatic
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    Thread Starter

    Re: 97 deville p420 code

    g'damn emissions!! well it has just 100,000 miles on it. the previous owner said it has a mis to it but replaced the wires and 4 front plugs and cured it? it seems anyways. I am going to try and go over to midas today and see what they say about the vibration will let ya know... maybe the miss was/is a bad injector sending a too much fuel and overheating the cat???

  6. #5
    Concourson20s is offline Cadillac Owners Member
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    Re: 97 deville p420 code

    sounds like the car just needs a reefa service

  7. #6
    fullserviceman is offline Cadillac Owners Fanatic
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    Re: 97 deville p420 code

    I gave it some high test fuel, a little injector cleaner additive, and gave it a few WOT treatments which caused the p420 code to go away and my wife to yell at me.. so far after 350 miles it is not coming back... The front end vibration was caused by a bad spot in my front tire. now car runs and drives like new...

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