2005 Coil Pack Wiring Harness Disaster
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, 2005 Coil Pack Wiring Harness Disaster in Past Cadillac Vehicle Discussion; I am a Car Dealer in North Charleston SC and have been a Mastertech since 1985 - however I have ...
  1. #1
    Carcollector is offline Cadillac Owners Member
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    I am a Car Dealer in North Charleston SC and have been a Mastertech since 1985 - however I have some not so masterful mechanical help at my business.

    I have a really nice 2005 Deville that I sold and traded back in - once in a while when I got it back it would trigger the Check Engine Light for a cylinder 8 misfire, we put plugs in it before I sold it about 1200 miles before traded back in. My guy pulls the coil packs out and the clips were falling apart especially cylinder 8. We couldn't find any of the short harnesses in the junkyard and apparently the harnesses and coilpacks they used from the factory are obsolete and are supposed to be upgraded due to cracking/breaking etc 2004 and 2005 models only.

    SO my Guy finds that the same year 6.0 clip ends are the same so he grabs those harnesses and foolishly cuts of the main plug ends and splices them and put them in the Caddy and tried to start it but it had no spark and it blew the coil fuse a few times. Another guy tried to bail him out by splicing just the ends to Irina harnesses but he matched color for color and he had the power running to the ground and vice versa because the clip plug was upside down the clips weren't exactly the same they were wired differently.

    So I take over and rewire everything, it stops blowing fuses, but has primary coil wiring codes on cylinder 1, 5,6,7,8 consistently, starts but only runs in 2,3, and 4 I guess it sounds sick like running on only a few cylinders and check engine light flashes. So I searched high and low and found 2 good OEM Cadillac coil harnesses new battery etc and I'm getting the same codes P0351, P0355,P0356,P0357,P0358...

    With a test light it looked like the grey wire had no ground signal on the cylinders with an issue and the ones that fire show ground on all wires except the power wire before I replaced harnesses but don't think that's the issue. The trigger wire and the grey wires were crossed from upside down wiring and I think it might have shorted something.

    My first instinct is that the PCM is fried

    If I have to replace the PCM/ECM are they plug and play from the same year model or will it have to be programmed?

    Or what the hell else could be the issue?
    It 's not the wiring at this point but haven't checked all the fuses yet just the coil fuse under hood

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  3. #2
    Carcollector is offline Cadillac Owners Member
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    Thread Starter
    Anybody have any input?

  4. #3
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it.
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    Re: 2005 Coil Pack Wiring Harness Disaster

    My only suggestion is to use the car's built-in trouble code scanner/memory to see if there's something in there.

    Use the sticky thread on the Deville main threads page - "How to pull codes" - use the correct model/year group of instructions - there's a link to all OBD-II diagnostic codes in the sticky, too.

  5. #4
    spotty is offline Cadillac Owners Fanatic
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    Re: 2005 Coil Pack Wiring Harness Disaster

    Quote Originally Posted by Carcollector View Post
    If I have to replace the PCM/ECM are they plug and play from the same year model or will it have to be programmed?
    I just went through a PCM replacement on my 2005 Deville. They are not plug-and-play: the VIN must be programmed into the new PCM. In addition to that, there are some further relearn procedures for the ignition keys and the crankshaft position sensors.

    I bought a used PCM on ebay and sent it to Wester's Garage to reprogram the VIN to match my car. You can also get a PCM from Wester's. The relearn procedures are performed once the PCM is installed in the car.

  6. #5
    Carcollector is offline Cadillac Owners Member
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    Yes your right has to be programmed.

    I am just hoping the issue is something other than the PCM but not sure what it could be besides however

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