hey if anyone can help it would be appreciated...anyway i have a 1990 sedan deville 4.5 and the fuel gauge is giving a few problems. first it was just the avg and instant miles per gallon flickering and just changing constantly and going crazy. and now sometimes if will just go blank and have a "d" illuminated, and then again sometimes it works just fine. im not sure if its the sensor on the pump or a module or computer of some sort, also sometimes once you turn the car off and come to restart the climate control will reset to 75 degrees. im not sure eif they are related but i'd think its more than likely. all ideas welcomed..

When a 'd' is displayed in the Fuel Data Center, it's either the FDC display, or the Body Control Module (BCM). Since it's acting so erratic, I'd suspect the FDC display first.

You can remove both the FDC and CCP and reverse the connectors. If the CCP displays a 'd' it's the BCM, if the FDC still displays a 'd', it's the FDC display that's faulty.

well ive changed both of them at one time or another, i changed the climate control because the lights were going out on it. and i changed the fuel gauge trying to fix this same problem b4 but i did get it from the salvage yard so its possible that it was bad too. but this weekend i will switch them around and see what happens thanx...

Start with checking the battery connections, battery and alternator output - the climate control reset to 75 is the default setting for a power cycle event like changing the battery and the other issues could be caused by low voltage. Seems like you are having power fluctuations. My first guess would be a bad battery.

I am having similar problems, however my fuel guage ONLY reads EMPTY all the time, however it calculates AVG MPG, INST MPG, and Fuel Used Correctly,
Could it be the same problem as listed here? Or a faulty fuel sensor in the tank?

I have the same problem and mechanic told me I needed a whole new BCM at a tune of a couple hundred dollars.

:thehand: BCM for a 1990 DeVille should be a $35 - $40 junkyard part. Changing them is not hard - they live right behind the glove box. I swapped mine several times and got to the point where I could do it in 20 minutes.

well the connections are fine i removed the b/s rubber on the terminals and have a new battery and alternator... the body control module does sound about right though and there is a pull a part here in atlanta so it should only be about 20$ but i will post with the results when i change it this weekend...

well the connections are fine i removed the b/s rubber on the terminals and have a new battery and alternator... the body control module does sound about right though and there is a pull a part here in atlanta so it should only be about 20$ but i will post with the results when i change it this weekend...

Just make sure you disable the airbag system before you go in - you have to move the DERM (Diagnostic Energy Reserve Module) to get the BCM out. The procedure is basically:

1) pull the airbag fuse, I also disconnect the battery
2) remove the glove box (5 or 6 screws)
3) loosen the 3 (or 4?) 10mm nuts and move the DERM
4) remove the DERM bracket and 2 sets of 10 mm bolts that hold some airbag wiring and the BCM
5) yank out the BCM and swap it
6) reassemble in reverse order

I'm doing this from memory and haven't done it for over 3 months, so age and alcohol may have omitted a couple of smaller steps.

thanx CHUBBY...when i took mine out i saw the little box first and wasnt sure but then your advice came in handy....it was real strange because the service vehicle light would come on and the airbag light as well plus when the service vehicle soon light was on the a/c would not get cold......so hopefully this helps someone else b/c the body control module was the problem...and it gave off that many symptoms..and once again to all who gave advice thanx..2x