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1993 DeVille
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4 Posts
Discussion Starter #1
So I have my '93 DeVille, which I love, but there's some electronic problems that I really want to get sorted out with it. I don't know a whole lot about working on vehicles, but I'm clever enough to work my way around the internet and guides based on what you guys can suggest, so I'd appreciate any input.

The biggest annoyances to me right now are the fact that my fuel meter/fuel economy display isn't working. It will light up with green bars when I start the car, but then will go dark and not come back on. Every once in a long while it will pop on and will work the way it's supposed to, but that hasn't happened in a while.

Secondly, my AC controls. With the display/controls, like my fuel meter, there's nothing that shows up on the display when I turn the vehicle on (though the AC kicks on automatically. Doesn't blow cold because I need to get a hose replaced, but that's another problem that I just need to get the gumption to fix), and though the lights on the button controls still come on, pushing them to change the AC does nothing.

One thing to mention is that I, in the early days of owning the car (my sad ignorance), replaced the stock radio with an aftermarket head unit, since the stock did not work, and did not keep the stock radio. I'm aware that in a lot of luxury cars like this, the radio is also set to control various other aspects of the vehicle aside from just the sound, so I'm a little bit anxious as to whether or not that could be an issue. If so, is there any redemption for my folly, or am I just SOL as far as that goes?
 

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85 Coupe Deville 4.1 V8 & 4.3 V6 Deisel & 1970 Eldorado
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773 Posts
The radio has nothing to do with any of the systems you are having trouble with however. If the radio is installed incorrectly it can interfere with the BCM delivery of the Fuel and AC panel's gas florescent display's power supply. This supply (appx 15 volts) originates from the BCM. If any additional loads are placed on it the BCM will shut the supply down. The controls will still work but the display's will be blank.
You may also have a defective Fuel or AC panel (or for that matter a bad digital speedometer if so equipped). It could also be a bad BCM. A FACTORY SERVICE MANUAL will have a troubleshooting flow chart to diagnose where the problem lies. It would be a lot cheaper than trying to Shotgun in replacement parts in the hit and miss method of repair, With the manual, the procedure is relatively straight forward and not difficult. (suspect the radio wiring first)
 

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1993 DeVille
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4 Posts
Discussion Starter #3
Would the radio wiring still cause problems even with the aftermarket unit disconnected or turned off? I currently have 4 blown speakers (another annoyance in itself), and so haven't bothered to have the head unit turned on at all.
 

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70 Deville 77 Fleet 78 Seville 92 Deville 03 Deville
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3,310 Posts
Since both displays are messed up, I would say you have a bad BCM. They used to be plentiful on ebay, maybe they still are.
 

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1993 DeVille
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4 Posts
Discussion Starter #5
New development - I just had my radiator replaced (as it was clogged like crazy, and nobody locally cleans them), and took my car out for a mini stress-test to see if my overheating problem had been taken care of. Long story short, it doesn't seem to have been, however after some time driving, I noticed my fuel meter turn back on, and then a few miles later, my AC display turned on, and the controls started working.

I've repeated it a couple of times, and from cold-start neither display works, but it's consistent that after ~10-15 miles of driving, they both turn on and start working for me, until I stop the car and let it cool down.

Any ideas?
 

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1991 Cadillac Sedan deVille
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591 Posts
You could have some cold solder joints (possibly in the BCM since both displays are affected), wiring issues, or one or more capacitors going bad (BCM most likely as well). Shortly after I bought my car my FDC started showing a c (clock problem), and then would do pretty much what both your FDC and ECC are (start working after a couple of minutes of driving or not at all). I remember I ran an extra data wire from the BCM to the FDC and I had the same outcome. Tried a reman BCM and I still had no improvement. So, I decided it was most likely some bad solder joints in the FDC itself. I opened it up and looked for obvious cracks in the solder, but didn't see any, so I reflowed all of the solder on the board. The result - my FDC has been working flawlessly ever since.
 
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