Last year, my dash started throwing seemingly random errors after driving around for a bit. Stuff like:

• Service Charging System
• Service Fuel System
• Low on Fuel
• Service Traction Control System
• Service column lock

The dash’s gas / temp / pressure gauges would zero out randomly, the CEL would come on, Traction control light, ABS light would illuminate, etc.

This was an annoyance at first, but last year it got bad when the car wouldn’t start. Everything seemed fine - full dash functionality, systems were go, but trying to turn over just failed and the car would go dark.

This led me to think it was something in the charging system. A quick test at autozone said everything was fine, but just to troubleshoot, a friend replaced the battery end cables, terminals, and battery. This got it turning over somehow, but the problems weren’t gone. Intermittent failures to start, dash lights freaking out, etc were still there.

We then started testing all of the cables and fuses one by one. Nothing definitive was found, but in the process of moving stuff around, unplugging stuff, etc, somehow managed to “fix” the problem for the next ~6 months. I replaced the alternator soon after for good measure too, and never saw the problems again, until recently. Same intermittent dash / starting issues. I got some clip installed below the steering column by GM through a recall, but this didn’t alleviate anything.

Last night, the car wouldn’t turn over. Jumpstarting did nothing. Pushstarting did nothing. The first couple times, I could just hammer the start button or unplug/plug the battery back in with varying success. But most recently, the car was totally unresponsive, with the dash lights / radio illuminating randomly, only one of the parking lights turning on (passenger side), brake lights / blinkers / hazards / headlights / seats not working, AC working sometimes, but never starting. The battery was fine.

We noticed some water under the battery, so my friend looked under the passenger-side dash, where the BCM is. He noticed some moisture in the area but nothing directly on the BCM. My car does smell like mildew after it rains and the floor mat on the passenger side gets damp, so we’re theorizing that maybe the cause of this is related to moisture-induced corrosion on some of the connections / wires leading to / from the BCM. We don’t think it’s the BCM itself because of how intermittent the issue is, and because after removing the BCM and plugging it back in, everything was 100% perfect. I'm also trying to avoid dropping $2+k on a “possible” fix if I can try a bunch of cheaper alternatives first.

We don’t know what’s causing this, but I’d like to post this in hopes that someone has experienced the same symptoms and might have some recommendations. I've seen many threads on the issue but a lot are pretty old with not a ton of replies - though I'm sure I haven't seen everything so any links would be helpful too.

We’re going to try to clean up some of the connections in the following days/weeks to try and safeguard the electronics from moisture as much as possible, and then try to identify where water is making its way in, but this is all without any certainty that the problem will be solved. Any insight from the community would be awesome - I’ll keep this updated as/if we discover anything along the way.

Relevant Details / Mods:
* 2005 C6 Z51, 80k miles
* Steering column fix
* OBX Headers

Pics of the dash when it happens while driving:

http://imgur.com/GA7G9p7,TtVw03k,QAxSrXU

 

I think you're on the right track. That big connector on the BCM has been discussed as the cause of a myriad of odd problems. If any moisture has gotten in there.......well you know.

Take it off, get the pins out of you can, check and clean everything with elec contact cleaner, put it back together with ample dielectric grease.

And find and fix your leak.

 

Your air box drain line is clogged, and why it's flooding the passenger side.

You need to either pull the drain line and clean it out, or at least put a small piece of wire up the drain opening to clean it up so the box can drain correctly.
Note, the water in the air box comes for the AC coils that traps the humidity in the air and turns it to ice, and as the ice melt off the coil, this is the water that the drain line allows to drain out. Also to note, the AC works both when you have AC on, but also when the heater is on to pull humidity out of the car/air too.

This the drain hose;



And this is were it's located on the back fire wall just to the right and down of the battery location,

 

My car had a major electrical gremlin which resulted in the car going into safe mode, rough idle, motor dying at low rpm, loss of shocks, loss of ability to get into reverse and a myriad of other things. Car was throwing code p0641 (5 volt reference system).

Turned out to be a frayed electrical harness going from the computer to the rear of the car (transmission tunnel harness). The 5 volt reference wire and the 12 volt wire had frayed against a metal bracket that is used to secure the harness to the back of the motor. I only mention this because you are having problems related to fuel and shocks.

 

Battery Age? Has it been load tested? Bad battery or connections gives many strange electrical gremlins. Also worth checking the battery cable connector at the starter. A loose or corroded connector there frequently is a source of electrical/non-start problems.

 

Thanks guys. I'll try the above recommendations.

This happened to me two more times this weekend and all I did was go under the passenger-side dash and wiggle stuff around to get it working both times. I guess that means it's *definitely* a wiring / connection issue, maybe caused by water from that clogged line.

RE battery age - it's less than a year old, and doesn't have any problems according to the dealership.