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Discussion Starter #1
I have a '94 Fleetwood Brougham, with an intermittent BCM. The dealership want's close to $800 for the part.

The wiring harness is fine, and I've designed and built a circuit to generate the PASSKEY signal to the engine PCM. By bypassing this function of the BCM, the car is now drivable at least.

Most functions of the BCM don't function full time. The BCM actually seems to work more often in cold temperatures than in warm termperatures, and because of this the car sat much of last summer, whereas it was driveable during the winter.

I need a source for schematics for BCM part number 16197386, so that I can trouble shoot the module internally. It seems as if the BCM doesn't recognize when the key is turned on. Some symptoms are; the delayed interior lighting doesn't go out when the key is turned to the on position, and the twilight sentinal headlights don't come on in the dark. The "PASSKEY FAULT" light flashes intermittently, but with no regularity.

Just as intermittently, everything will work just fine.

HELP!!!

At least help me with a phone number internally at Cadillac so that I can call someone there!

PrestonIII
 

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Discussion Starter #3
I have no idea what that "bump" means.

PrestonIII
 

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You may have tried this already, but disconnect the battery cables from the battery for about 20 minutes. Before you reattach them to the battery, touch and hold the cable ends together for about 30 seconds. Sometimes it actually works to reboot the BCM.

If that doesn't work, have you tried taking the cover off the BCM and spraying it with a cold spray in spots to narrow down what's heating up and making it run bad?
 

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Discussion Starter #5
Oh, I've tried it all! And I've had the BCM on a test bench for two days. It usually works at typical laboratory 70 degree temperatures. But put it in a black car in the sunlight, and those temperatures exceed that easily. My Fleetwood Brougham is tripple black.

I'm quite positive that the BCM has an internal power supply problem, and I've had it apart on multiple occasions. It is surface mount electronic construction, and therefore tracing the circuitry inside is nearly impossible. Simply put, I need a schematic diagram to do the troubleshooting.

I've seen schematics of MANY of GM's computers on the internet, but I have yet to see one of this BCM. Does ANYONE know who to contact at Cadillac?

It would not be easily possible to use a used BCM for this car, because the BCM in the '94 Fleetwood Brougham uses the chip in the ignition key to activate the PASSKEY/VATS system to allow the engine computer to run the fuel injection. Changing out the BCM with a used one would involve changing the ignition key to one with the proper chip for the used BCM, and the scrap/wrecking yards are not usually able to tell you about the chip from the original wrecked car. So, there's no real way to activate the used computer in my car, unless "luck" played in, and it used the same chip as my original, and that is not likely. At this point, I would be in the same boat that I'm already in.

GM and Cadillac have you locked up with this. The only real way to fix the problem is to replace it with an $800 NEW piece. A new BCM "learns" your original chip value when you first install it in the car, and will only work with that particular chip value afterwards. They are not reprogrammable. If they were, I could use a used one from the scrap yard.

Another thought: if they were programmable, that would defeat the security purpose of PASSKEY/VATS: crooks and thieves would just reprogram the computer to use whatever key they happen to have, or no chip at all, like a screw driver. The police car and taxies all have VATS/PASSKEY too, but the keys have no chips (cheaper to make multiple of copies), and the various associated PASSKEY/VATS/BCM modules program themselves accordingly.

What are we going to do in a few years when GM no longer makes a replacement part? Sooner or later, someone is going to need a schematic. For me it's "sooner".

PrestonIII
 

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2005 CTS-V, 1994 Infiniti Q45
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Why dont you go to a junkyard and replace it with one.... 94/95 BCM should work just fine.....

YOu should be able to get one for like $100
 

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There are 13 differernt resistance values for the passkey system. Trial and error with a few resistors may be the best option. I will try to look up the values for you if you want to give that a try. The "bump" was to bump this question back to the top of the new posts, to help you get an answer to your question.
 

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Discussion Starter #8
I have thought about the issue of creating a key to match a junkyard BCM.

As I unserstand it, the BCM will shut down for a long period as it recognizes an invalid chip resistance. This is the "security" aspect of PASSKEY/VATS. This being the case, I'm not sure how long it would take to even try each of the resistance values available (I have seen the resistance values posted at various internet sites), nor how I would specify a different value to the locksmith or dealership to make a new key with my tumbler cut, and a different chip value.

As an electrical engineer, the schematic sounds easier to me, and sooner or later may probably be an asset to all of us with the big Broughams, as rare as they are.

PrestonIII
 

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The actual list on the BCM is $645.87. After all is said and done, it may be easier in the long run to check out one of the places that discount GM parts and pick up one for even less than that.
 

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Hey Preston have you figured out the problem or have received your schematics yet?


I know someone else witht the same problem and I have the same problem. Not as severe though, My only problem is that the BCM must not be recognizing the key resistance, or so I thought, after bypassing the key resistor I still have the same problem, but my problem is more prevelant in cold weather instead of warmer temps.

I have cracked the case open on the module looking for a suspect solder joint but didn't find anything.
 

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Hi, failed BCM module. Do you still have that? If you do would you be willing to give it away. I need some of the circuitry inside and ,obviously, dont want to pay for a whole new one. Ill gladly pay for the shipping if you would give it up.

email me at :

chibski at knology dot net

Thanks,
Chris
 
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