On my 99 Grand Am SE, I have lost the analog dashboard gauges, the digital odometer, the warning lights (except check engine soon, which comes on steady sometimes), the HVAC system, the rear defroster, the cruise control, the daytime running lamps, and the fog lamps. The radio, wipers, power windows, power locks, interior lights, tail lights and automatic headlamps still operate. Also, the dash warning lights do work when the key is in Accessory, but not in On position. Have checked all fuses, as well as any relays and connections I could find and not found any problems. Even tried a temporary new ground between the engine and the frame with no luck. Borrowed an OBD-2 scanner and got codes 1665 and 1676. The problem used to come and go randomly and for a few seconds at a time, but now everything is off much more often than it's on, making the car virtually undriveable. A mechanic and a few other people with repair experience are stumped at this point. Any ideas on where to look for the problem or what to do next are greatly appreciated!

Also, are wiring diagrams available for this car?

Check the Body Control Module. It probably went bad and is causing the majority of your problems. It isn't too expensive to replace and you may even be able to find a good used one.

Thanks. I have been unable to find a wiring diagram. Is this located under the glovebox, in front of the blower? I found a black box with three blue connection points on the right-hand side and a heck of a lot of wires converging on those connection points when I was checking for wiring problems. As I was checking for loose connections, everything came back. Not sure if it was coincidence or I've stumbled into the right place. My reason for looking back there is that many of the components that are not working have fuses in the passenger-side fuse box. I couldn't find anything to indicate a part number that I could look up, though.

the bcm will require a vin number to get you the correct one, as different options require a different BCM

I have been having the same exact problems with my '99 SE. Same codes from the computer as well. I've already replaced the bcm, problems still exist, same codes being set, Service Engine light still coming on occasionally. Checked local grounds around the bcm, they looked good.
After some thought, I'm thinking of replacing the ignition switch and lock cylinder, as I'm wondering that's it's cutting off power to the bcm and causing a reset, (the wiring diagram shows ignition power going to the bcm via ignition #3 wire as well as a wire from the passlock in the cylinder).

I'll update if I find out anything else. I'll also open to other ideas....

- Eric

The BCM is what validates the r-code of the lock cylinder for Passlock and the timing of the lock cylinder to the ignition switch, that's why those wires run to the BCM. If all is good the BCM tells the ECM to allow the engine to start.

On my 96 GA SE my car one day I started in up and nothing electroni would work, power windows or AC and it was the middle of the summer. I drove to a friends about 2 miles away. and just let it be. About an hour later I left and it all worked. I never figured it out either

This sounds more and more like an ignition switch problem then. If the wire sending a passlock signal to the bcm becomes intermittent, it probably makes the bcm think the car was shut off, so it goes to sleep and turn the gauges and accessories off. When the wire comes back, it wakes the bcm up, resets the gauges, and sends an 'okay to start' signal to the pcm, which causes a momentary miss in the engine, (at least for me, you can feel the engine miss at the moment the gauges reset), and in confusing the pcm, sets the two codes that we're seeing - one for fuel level output, one for the evap purge solenoid, (probably because they're in the wrong states - the pcm is expecting them to be at an engine-off state if it just received an okay-to-start, but the car is actually running and their states are different).
Just my $0.02, but it makes sense. I'll change the ignition switch next week and see if that resolves the issue.

- Eric

I located the BCM and checked wires going to/from it. While I did not find anything loose or out of the ordinary, while I was checking, everything came back. I removed all connections to the BCM and reattached, hoping something had just worked its way loose. So far, so good since last Thursday. Based on what I've read here, I'm wondering if the connection between the ignition switch and the BCM had loosened. I could feel the miss in the engine when my gauges and everything went out, too. Also, while everything was out, the transmission felt different, especially when going from 1st to 2nd.

As far as the tranny feeling funky, the module for the tranny is also tied in there. It's like a crazy web from the GM Black Widow Spider...

I've installed a new ignition switch, (the switch itself, not the lock cylinder), and I haven't had gauges go funky on me, at least not yet. Took about an hour or so altogether. After installing the new switch, the key feels firmer and the detents in the key are firmer, with less play. I didn't realize how much play had been building up in the switch over the past 5 years.
I have a feeling this fixed the problem for me. The switch is part # 22670487 from GM, or AC Delco part #D1432D. You can get one from www.rockauto.com for $80.
Unless you're having problems with the car not starting and having the security light on the dash stay on, you don't need to buy a new lock cylinder. But if your gauges and interior components are having issues, it's time to check out the BCM AND the ignition switch.

- Eric

So far I'm still doing OK after checking the contacts on the BCM. I'll keep the ignition switch/BCM combo in mind if the problem returns. There seems to be some debate in this forum over the BCM and the passlock security. Does a new BCM have to be programmed according to the vehicle's VIN?

At least for the '99 Grand Am, a new BCM does not need to be programmed in order to be used. You just need to have it recognize the code in the passlock code in the ignition lock cylinder:

Hook up the bcm, try to start the car, it will turn over, but not start.
Leave the key turned to ON in the ignition, wait about 10 minutes, the security light in the dash will go out.
Start the car.

That's it. Hope this helps!

- Eric

Well, I started having problems again. I replaced the BCM, but that doesn't seem to fix anything. I guess it's on to the ignition switch, unless anyone else has ideas. I talked to the service manager at a local dealership, and his best guess was the BCM, so I might as well keep pursuing this on my own. At least no money was wasted on labor...