P0420 and Some Questions
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, P0420 and Some Questions in Past Cadillac Vehicle Discussion; I am getting the P0420 code current (Catalytic converter efficiency low). the only other code I'm getting is P0741 (TCC ...
  1. #1
    redoxy is offline Cadillac Owners Fanatic
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    P0420 and Some Questions

    I am getting the P0420 code current (Catalytic converter efficiency low). the only other code I'm getting is P0741 (TCC stuck off) I have read alot about this code and come to the conclusion that its not worth the price to fix since the only effect will be a loss of about 2 mpg which I can live with.

    I think the reason for the code is the fact that the previous owner was driving the car with a misfiring and when I bought it i had to drive it to my city with the misfiring ( about 300km drive). I also noticed that the air pump was missing the underside cover. My guess is this resulted in sucking of debris into the CAT which may have clogged the CAT. I replaced the airpump about a week ago and still get the code after resetting.

    I know after-market CAT is frown on here so I called the local dealer and they wanted 1500$ for the replacement CAT.

    My question is what will be the effect of driving the car and not fixing the CAT in the mean time. Also can someone please shed more light on why after-market CAT is not good for our caddys?
    rockauto has an eastern catalytic direct fit CAT which will cost less than 200$ shipped.

    Thanks

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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: P0420 and Some Questions

    The AIR pump is not likely the problem. If the CAT was clogged you'd have driveability problems (no acceleration).

    The biggest problem with aftermarket CATs (to the best of my knowledge) is that they may not be efficient and may still trip the SES light.

    Driving the car without fixing the CAT hurts the environment, not the car, and of coarse you'll have to live with the SES light.

    I assume you have no emissions testing up there. You'd never pass one with that code and a bad CAT.

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    redoxy is offline Cadillac Owners Fanatic
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    Re: P0420 and Some Questions

    Thanks Ranger
    Yes we don't have emission testing here. And besides the SES light, I don't have any driveability issues at all
    car accelerates fine and i just returned from a road trip where i drove at high speed and didn't have any acceleration problem. And no problem passing also.
    So could it really be a bad CAT or maybe something else is the problem.

  5. #4
    98eldo32v's Avatar
    98eldo32v is offline Cadillac Owners Connoisseur
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    Re: P0420 and Some Questions

    You need a converter.

    The front oxygen sensor and rear of the converter oxygen sensor have a sort of "calibrated" window of efficiency programmed into the pcm.

    When the vehicle is running, the pcm is constantly checking and referencing this "window". When all criteria is met, the lite stays off. When the rear sensor starts reading almost as the front, the light comes on.

    You can attempt to change sensors, but I think that may prove to be fruitless.

    The best non oe option for a converter may be a Walker Direct fit converter.

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    redoxy is offline Cadillac Owners Fanatic
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    Re: P0420 and Some Questions

    Thanks 98eldo
    will look into the walker option.

    Has anyone replaced their CAT with after-market one and what is the experience? was it difficult to install?

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    thenaaks is offline Cadillac Owners Member
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    Re: P0420 and Some Questions

    this deville owner has an inexpensive solution to your ses light. mine would come on sporadically... clear the code, drive it another several hundred miles, and the light would come back on. i inserted the aft oxygen sensor in a modified spark plug non fouler. no emissions testing or vehicle inspections here. is it properly repaired? no. do i feel bad about it? no. i'm getting 25+mpg. my catalytic converter operating at below minimum threshold (or whatever) is not doing grievous harm to the environment. if i knew that a $200 aftermarket cat would permanently fix it, i might spring for one. but i'm sure as heck not spending 1/4 of the value of my car to buy an oem converter.

    so, long story short...buy a spark plug non-fouler ($5) and your light will probably stay off indefinitely.

  8. #7
    redoxy is offline Cadillac Owners Fanatic
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    Re: P0420 and Some Questions

    Quote Originally Posted by thenaaks View Post
    this deville owner has an inexpensive solution to your ses light. mine would come on sporadically... clear the code, drive it another several hundred miles, and the light would come back on. i inserted the aft oxygen sensor in a modified spark plug non fouler. no emissions testing or vehicle inspections here. is it properly repaired? no. do i feel bad about it? no. i'm getting 25+mpg. my catalytic converter operating at below minimum threshold (or whatever) is not doing grievous harm to the environment. if i knew that a $200 aftermarket cat would permanently fix it, i might spring for one. but i'm sure as heck not spending 1/4 of the value of my car to buy an oem converter.

    so, long story short...buy a spark plug non-fouler ($5) and your light will probably stay off indefinitely.
    I'm all ears Thenaaks. Can you give me some details on how to get this done? if you are uncomfortable typing here you can PM me with the details. I will definitely give it a try before spending an arm and a leg for a new CAT. because from what i have heard even if the cat loses something like 5-10% of its efficiency the light will come on.

  9. #8
    thenaaks is offline Cadillac Owners Member
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    Re: P0420 and Some Questions

    get this: http://www.oreillyauto.com/site/c/de...0259&ppt=C0334

    remove the rear o2 sensor...drill out the spark plug non fouler so the o2 sensor will fit snugly inside. thread o2 sensor into non fouler, then thread the assembly into the o2 sensor bung. the non fouler keeps the o2 sensor out of the exhaust flow, but it still gets hot enough that no dtc's are set.

    i'm sure that the epa and c.a.r.b. would cringe if they read this, but i don't care. i've seen too many cash for clunkers videos, where excellent automobiles were destroyed, to feel bad about circumventing the emissions system.

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    98eldo32v's Avatar
    98eldo32v is offline Cadillac Owners Connoisseur
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    Re: P0420 and Some Questions

    The anti-fouler technique works. Some times you may need two of them stacked together for really finicky cars.

    Good luck.

  11. #10
    PineyJustice is offline Cadillac Owners Fanatic
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    Re: P0420 and Some Questions

    Half way to a rebar special there, all you need to do is add a couple feet of steel to your cat and you never have to worry about a plugged cat again.

    Something else to consider, it might be a bad o2 sensor, especially if you have none of the other symptoms, either way that rear o2 sensor is a PITA to get at.

  12. #11
    mike5514 is offline Cadillac Owners Enthusiast
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    Re: P0420 and Some Questions

    autoparts warehouse has a walker cat for 156.00 49 state legal that will be great for your car you surely can afford that!. Mike

  13. #12
    wahhabm is offline Cadillac Owners Fanatic
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    Re: P0420 and Some Questions

    I installed an after market cat from canada, it didn't work, then I bought a walker Part Number 81909 Cal Cat since I live in california, and it did the trick. walker Part Number 81909. anyone who needs a good cat can buy this one for about 150 dollars

  14. #13
    redoxy is offline Cadillac Owners Fanatic
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    Re: P0420 and Some Questions

    Quote Originally Posted by wahhabm View Post
    I installed an after market cat from canada, it didn't work, then I bought a walker Part Number 81909 Cal Cat since I live in california, and it did the trick. walker Part Number 81909. anyone who needs a good cat can buy this one for about 150 dollars
    Wahhabm
    did you install it yourself? how difficult was the install and any special advice for anyone who intends to install one.

  15. #14
    wahhabm is offline Cadillac Owners Fanatic
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    Re: P0420 and Some Questions

    I had it welded by exhaust shop.

  16. #15
    redoxy is offline Cadillac Owners Fanatic
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    Re: P0420 and Some Questions

    I was afraid you were going to say that. Where i live shop rates are outrageously expensive. I will go with the walker quick fit on rockauto and use clamps then.

    Thanks

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