Have had this car for almost two years now. Soon after, I noticed several inches of water standing in the trunk with the spare tire. Replaced both taillight gaskets, but somehow water still is getting in. Starting about one year ago, every now and then I would catch the tachometer and speedometer drop to zero, and I would get a no power steering and stabilitrak warning in the dash. After about a second the car would return to normal. The problem has gotten progressively worse. About a month ago, when I was driving down the highway I could feel the RPMs kinda bouncing up and down, followed by the gauges going to 0 and the aforementioned warnings coming up. Pulled over and parked, and I noticed the transmission was stuck in a high gear. Turned the car off and it would no longer start- engine wouldn't even crank, held the key for 30 seconds and nothing happened. Eventually had the car towed to a dealership who said it was a bad battery. Driving back from the dealership and the problem reappeared. Car towed back to dealership and they kept it for a few days before saying it was because of a pinched wire above the transmission. Car seemed to drive fine for next several hundred miles, but has once again reappeared with increasing severity again. Scan with a cheap reader gives the following codes:
P0700: TCM MIL activation requested
U0073: Control module - data bus off
P069E: Fuel pump control module MIL activation requested
U0101: Data bus, TCM no communication
U0109: Data bus, fuel pump control module - no communication

Here are the symptoms I've noticed and remember:
Transmission stays in whatever gear it was in when the problem starts
No power steering
No stabilitrak
Speedometer and tachometer drop to 0
OBD reader can't connect
Air conditioning will stay on even with key out, blows unconditioned air when car is on
Car won't start sometimes, but usually will when key is held for a time

The problem is usually intermittent, only happening once every few days and usually resolves itself after a period of time- from seconds to hours. I can usually watch the gauges bouncing up and down, but lately they've been sticking at 0.

I was just wondering it anyone could provide any advice or thoughts. Could the water in trunk be possibly related? I know the fuel pump control module is located in the trunk, but would that affect everything else?

 

My wife's 2010 equinox is having the same issue. I cant find anything on the cause. Any updates from your experience? Thanks!