First off, I have a 2004 Monte Carlo SS. Anyhow, a few years back as the wife was driving out of town the warning lights flashed on, just like they do when starting the car, then went off, the guages to the left side dropped all the way they came back up, all the while the car continued to run fine. We took it to the dealer and they could not find anything wrong. Over the past few years it did it again a few times, the most times on one trip was twice, and we took it back to the dealer and they could not duplicate the event. By the way, it only seems to do it on long trips.

Last night while coming home from Vegas, which is about a 4 hour drive, it did it a total of 5 times. I noticed that tachometer and speedometer remained stable, just the guages on the left side drpooed then came back up rather quickly and all the warning lights briefly came on as well as the seat belt light flashed, like I stated earlier, just like they do upon normal startup.

So, WTF is going on? Can anyone please help me out?

 

I had the same symptoms with my 2001 3.4 ls and it turned out to be the ignition switch, I did not have to replace the ignition key cylinder which fits inside the switch.

My problems originally started with the passlock security system not letting the car start which I got around by leaving the key in the on position for 10 minutes and then the car would start. It then progressed to abs/brake/traction control/airbag lights etc. freaking out. This would happen while driving (and clear itself within a couple of minutes) and finally getting to the point where it would do that when trying to start the car.

Thankfully it was not the bcm module since the ignition switch was only about $40 which I replaced myself.

Can't say for sure that you have the same problem but it sure sounds similar. Check my previous postings for input from other members and good luck with it!

 

Just an FYI with additional info:

I replaced my ignition switch with a Dorman brand part #924701. That switch is also listed as being the replacement for your 2004.

 

I have the same problem with my 2002 SS. I replaced the ignition switch for other issues along with the gauges resetting. The new ignition switch fixed my other issues but it sadly didn't fix my gauges. They still randomly reset and sometimes the car will even chime like it does when you first start it. The dealer said my gauge cluster is going bad. I also heard someone talking about a group of wires under the air filter box that can get rubbed thru and cause these symptoms. I have to check my wires there and see if they are ok. Maybe I will get lucky and that will be my issue....if not I guess I am trying a new gauge cluster.