Mechanics

WIRING PROBLEM

1995 Pontiac Bonneville

Electrical problem
1995 Pontiac Bonneville 6 cyl Front Wheel Drive Automatic 200000 miles

I am working on 1995 Pontiac Bonneville for a friend. She was on the highway and said the car just died and wont start, so I had her tow it over to my garage. After the truck dropped it, it started right up and died about a minute later. I checked and it was getting spark so I figured fuel pump. After pushing it in my garage I also noticed that the power windows, locks and seat were not working. I called and asked her if they were working prior to the car breaking down and she said yes. So now I am thinking an electrical problem. Battery is brand new by the way the car cranks strong. So I started by checking the basics, fuses are all fine both under the hood and dash. The relays all seem to be fine. I also noticed the the indicator light on the rear defog button is on even with key off and when you press the button with the key on it shuts the dome lights off. All very strange. Now I have all the wiring from under the dash to about the sides of both front seats pulled up and there does not seem to be any obvious frayed wires or cross shorts. I was playing around with the fuse and relay center when suddenly everything started working for a short moment but then stopped. I was hoping I had it traced to that area but have not had anymore success. Is there possibly a computer that controls those things that I don't know about? I'm a pretty experienced mechanic but this problem has me at wits end. I have been working on this car for 2 weeks. Please help and thanks so much!
Avatar
Jeromeleahy
June 29, 2010.



The power window and power seat use circuit breakers. Did you check for voltage at the circuit breakers? The voltage for the ps breaker is hot all the time. Voltage for the pw breaker goes hot with the key on. With multiple issues, I track one circuit, I look for voltage and ground to start. Fixing one circuit may or may not fix everything.

On the other issue, did you use a gage and check fuel pressure? Any applicable trouble codes?

Tiny
Internetmechanic
Jun 29, 2010.
Yes I did use a gauge to check for fuel pressure and no trouble codes. The voltage at the breakers is present. I'm almost sure its a cross short. I worked on a geo with an intermittent fuel pump problem that was because of a short with a frayed wire that when you would step on it, it would cause the fuel pump to cut off. It was just way easier to find because the car had no power accessories.

Tiny
Jeromeleahy
Jun 29, 2010.
With good fuel pressure, good spark, and injector pulse, I can usually get the engine to hit.

Tiny
Internetmechanic
Jun 29, 2010.
Did you find the problem? I am having the same exact problem with mine. My stepdad has changed coil pack, ignition module, computer, ignition switch, new key switch and key and it is still doing the same thing, it ran for about half a day after he did the coil and ignition module but right back to the same problem

Tiny
Misfitlady
Jul 3, 2010.
Yes I did as a matter of fact. It was the BCM (body control module). Its located under the passenger side dash. It controls all of the interior electrics and the fuel pump. Dealer wants $500 but I got mine from the junk yard for $75. Good luck!

Tiny
Jeromeleahy
Jul 3, 2010.
Thank you so very much, my dad and brother were completely stumped and I couldnt afford to keep replacing everything

Tiny
Misfitlady
Jul 3, 2010.
Bonneville SE has no bcm control of windows or seats, according to MOD. There is more than one class of bonneville, though. So you need to know, pontiac bonneville.

Tiny
Internetmechanic
Jul 3, 2010.
Yes SE but everything is exactly the same as the original question right down to the rear defog, let me go to the garage and make sure its SE, no its just a bonneville and the book they have they cant find where the BCM is or what it looks like

Tiny
Misfitlady
Jul 3, 2010.
It doesn't matter if its SE or not bud. When you buy the module all they ask you is if you have the anti theft system or not. Supercharged does not matter either. This is an interchangeable part with many GM models so no big deal finding one. Good luck and let me know if that helps you and fixes the problem.

Tiny
Jeromeleahy
Jul 3, 2010.
Hey, I've been wrong before. Show me the wiring diagram where the bcm controls the windows and seats. I'm just trying to understand. I enjoy talking to you, I'm always willing to learn. Thanks

Tiny
Internetmechanic
Jul 3, 2010.
Page 1 of 2