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Northstar Engines and System Technical Discussion Discussion, P0420 Code in Cadillac Engine Technical Discussion; Originally Posted by ewill3rd If you bought an aftermarket cat, take the car back and have them install the right ...
  1. #16
    1stkobefan is offline Cadillac Owners Member
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    Re: P0420 Code

    Quote Originally Posted by ewill3rd View Post
    If you bought an aftermarket cat, take the car back and have them install the right one.
    Legally they have to provide you with one that will do the job the GM one did. Many aftermarket ones have trouble meeting the requirements to pass the on board diagnostic tests... which means they don't work.
    Who are "They" cuz I recently bought an 02' DTS that's got an aftermarket Cat & I just can't afford the $900+ it cost to replace it with the GM factory Cat. I just had the Cat replaced & the SEL came back on 3 days after I had it replaced. Plz HELP.
    Also where are the spark plugs located on the 02' DTS. Thanks.

  2. #17
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    Re: P0420 Code

    You'll have to fight out the cat with the selling dealer. If the SES light was on when you bought the car, I have no idea of your recourse. The Northstar series of FWD cars hates aftermarket cats: they supply nothing in the way of reduced restriction (there isn't any to speak of) and almost always seem to cause DTC problems.

    The spark plugs are down in wells inside each cam cover, connected by conductive boots to each of 8 coils in the pack cassettes which are set into the cam cover tops. The cylinder heads are technically 4-valve semi-hemi (penthouse) units with the spark plug in the center of the 4 valve array. The plugs are ACDelco 41-987 Double Platinum units (ONLY) and can be obtained from one of several outlets used by most of the CF members: It's all in here and Seville/Deville. 100,000 mile replacement.

    (retired QMCM (SS) (DV) COB, all subs)

  3. #18
    1stkobefan is offline Cadillac Owners Member
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    Re: P0420 Code

    Quote Originally Posted by submariner409 View Post
    You'll have to fight out the cat with the selling dealer. If the SES light was on when you bought the car, I have no idea of your recourse. The Northstar series of FWD cars hates aftermarket cats: they supply nothing in the way of reduced restriction (there isn't any to speak of) and almost always seem to cause DTC problems.

    The spark plugs are down in wells inside each cam cover, connected by conductive boots to each of 8 coils in the pack cassettes which are set into the cam cover tops. The cylinder heads are technically 4-valve semi-hemi (penthouse) units with the spark plug in the center of the 4 valve array. The plugs are ACDelco 41-987 Double Platinum units (ONLY) and can be obtained from one of several outlets used by most of the CF members: It's all in here and Seville/Deville. 100,000 mile replacement.

    (retired QMCM (SS) (DV) COB, all subs)
    So these are the only plugs i can use? Cuz I bought 8 of the Bosch Platinum 4. So would u suggest me trying to change them myself or just pay to let a shop do it. The front seems easy but the back would be near impossible. Thanks for sharing the knowledge.

  4. #19
    ewill3rd is offline Cadillac Technician
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    Re: P0420 Code

    Two pieces of advice.

    #1. Don't use Bosch platinum plugs in a GM engine. They won't run right and it may even cause some real drivability issues for you. Look over the forums and read the stories about how people had poor running cars until they put stock plugs back in.

    #2. If you don't know where the spark plugs are, I'd recommend you pay someone to put them in. It could be expensive depending on where you live but it might keep you from running into some potentially serious problems.

  5. #20
    AJxtcman's Avatar
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    Re: P0420 Code

    Quote Originally Posted by ewill3rd View Post
    Two pieces of advice.

    #1. Don't use Bosch platinum plugs in a GM engine. They won't run right and it may even cause some real drivability issues for you. Look over the forums and read the stories about how people had poor running cars until they put stock plugs back in.

    #2. If you don't know where the spark plugs are, I'd recommend you pay someone to put them in. It could be expensive depending on where you live but it might keep you from running into some potentially serious problems.
    I second that

    I had a coworker about 10 years ago that had a 67 Camaro (not stock) that ran 12 second 1/4's. He had Bosch Platinum plugs in it. He put them in every car he or his family member had. I informed him that the Bosch plug was not the best for his application.
    We did a test.
    He pulled the plug and installed AC Delco Rapid Fire plugs. This plug is very similar to the AC Delco Platinum or Iridium plug.
    He ran a quicker time at the track and he said that he had better throttle response.

    The Bosch plugs he removed had buildup on the porcelain portion of the plug. The design of the plug will allow for this type of build up. A Northstar can burn oil. The mix of those two will lead to a possible misfire or weak spark.

    I was a drivability tech for about 7 of my first 12 years. I didn't have a hoist most of the times. I have changed a lot of spark plugs and I can tell you that the Bosch Platinums are on the bottom of my list. I have seen a lot of gimmick plugs over the last 22+ years and them and Split Fires are at the bottom.

  6. #21
    ewill3rd is offline Cadillac Technician
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    Re: P0420 Code

    Oh and for the guy above, the installer is required to warranty the part for like 5 years or something, you can find more information on EPA regulations regarding converters online.
    If you know where the cat was put on, take it back and have them replace it until the light stays off, the law requires them to do just that.
    If they put a catalyst on that doesn't do the job that the original did they are in violation of Federal Law.

  7. #22
    1stkobefan is offline Cadillac Owners Member
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    Re: P0420 Code

    Quote Originally Posted by ewill3rd View Post
    Oh and for the guy above, the installer is required to warranty the part for like 5 years or something, you can find more information on EPA regulations regarding converters online.
    If you know where the cat was put on, take it back and have them replace it until the light stays off, the law requires them to do just that.
    If they put a catalyst on that doesn't do the job that the original did they are in violation of Federal Law.
    So if the dealer sold it to me like this are they liable? If i change the O2 sensors to universal also, will that make it read within limits u think? Thanks every1 for the sparkplugs tips.

  8. #23
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    Re: P0420 Code

    Quote Originally Posted by 1stkobefan View Post
    So if the dealer sold it to me like this are they liable? If i change the O2 sensors to universal also, will that make it read within limits u think? Thanks every1 for the sparkplugs tips.
    If the O2 sensor was the problem it would set an O2 Sensor code.

    P0420 is a code that states that the post converter O2 sensor is switching at a similar rate and or voltage as the manifold O2 sensor.

    Basically the post O2 need to switch at a slower rate by X% and the peaks in voltage need to be X% less.
    Just say the cross counts need to be 25% of the Manifold O2 and the voltage swing needs to be no more than 20% of the Manifold O2.

    A P0420 will set when both O2 are switching at the same rate and the same voltage.

  9. #24
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    Re: P0420 Code

    As to whether or not the dealer is liable, that depends on the laws in your state.
    You might contact your local highway patrol office and see if they have someone that can specifically answer your questions.
    If you didn't buy the cat you might have some issues... mainly just the expense of fixing it right yourself.
    It could get someone up the chain in trouble for putting a substandard emissions part on the car.
    The law actually requires a pretty long paper trail, but as I said there can be variances from state to state.

  10. #25
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    Re: P0420 Code

    Hey Guys, i'm having a problem lately and i wanted some feedback on the same code that is popping up on my car.

    Recently i had the Front Cyl. Coil Cassette Pack go on my 2002 SLS. I replace the Pack and put new Delco Platinums that are the OEM plug #. I have since the repair gotten twice the PO420 Code. I will go and clear it and it came back a few days later. First time it happened i was on a long car ride. Second time was on the way home from work.

    I seem to think that if my car was run under this bad misfire condition that this will cause the code to come up, right?

    Should i just give it some more time and see if it keeps coming up? Or should i get a new Cat.....

    Car only has 59,000 on the clock. Would the GM Emissions warranty cover this problem???

  11. #26
    ewill3rd is offline Cadillac Technician
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    Re: P0420 Code

    The coil failure may have damaged the cat. It shouldn't take long after repair for the cat to clear out.
    It takes a certain set of driving conditions for the test to run, not surprised it doesn't happen often.

    I'd take it in and have them look at it, you'll probably need one replaced.

    I woudl run the VIN to be sure but on most cars the cats and ECM are 8/80 coverage.

  12. #27
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    Re: P0420 Code

    Quote Originally Posted by ewill3rd View Post
    The coil failure may have damaged the cat. It shouldn't take long after repair for the cat to clear out.
    It takes a certain set of driving conditions for the test to run, not surprised it doesn't happen often.

    I'd take it in and have them look at it, you'll probably need one replaced.

    I woudl run the VIN to be sure but on most cars the cats and ECM are 8/80 coverage.
    hey guys i'm finally getting annoyed with the SES light coming on again and again. I'm gonna take it to the dealer. The car is under warranty for emissions equipment still.

    I have a question about dealing with the dealership. Do they have to do diagnostics on the car first before considering it's the cat? I really don't want to get stuck paying for anything else. cause i can go to a shop of my own and get other things that could be broken done cheap. I'm only taking it to the dealer cause i seriously feel it's a cat issue and it's covered under warranty.

    Any feedback would be great.

  13. #28
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    Re: P0420 Code

    Tell them not to touch anything that is not covered.

  14. #29
    ewill3rd is offline Cadillac Technician
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    Re: P0420 Code

    They can't do anything (in most states) without your prior approval.
    They might ask for authorization on some checkout time up front in case it isn't a covered repair and you should only be responsible for what you agree to ahead of time.
    It can be a pretty weird thing depending on the advisor you get. Most will prep you for some expense, they cannot just go on and on and check it all out and then try to charge you.

    They can't spend your money without your authorization, make sure to ask them each time specifically what the costs will be as you progress through your visit. Make them be clear and concise, make sure they understand if you don't agree to it beforehand you aren't paying for it.

  15. #30
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    Re: P0420 Code

    I just was looking on GM Parts Direct and they list that for the cat converter and the rest of the exhaust behind it is sold as a kit for 1200 bucks?????

    If the dealer has to replace the cat can they just replace the cat or do they have to replace the entire exhaust system????

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