Hello this happened about 6 mo ago and suddenly everything worked fine. The dash gauges would not power up on start.They would power up with my Tech2 but not when the car started(05 C6). The problem fixed itself and now after 6mo happened again. When I start it the gauge display does not come alive at all.I think the BCM controls it but wondering if anyone had seen this before. No codes nothing.
Ok 4/19/2020 I connected my Tech2 and did a Gauge Sweep and nothing happened either individually or as a cluster nothing moved. Next I unplugged the connections at the BCM and plugged them back in.Then pulled the fuse for HUD/INST cluster 15 amp that was ok. I started the car and nothing stell dead. I was pissed so I tried the hit it to make it work method and it worked. Shut it off and restarted it still works so I guess I have a poor connection on the back of the Instrument cluster. now when the weather gets warmer I'll pull it out and check it. I read that its not a big job to pull the cluster out.
P.S using the Tech2 is great you can command everything in the vehicle on or off. If you get a chance to buy one do it . Mines a clone and paid for itself already. Any advice on removing the cluster would be appreciated thanks.
I tried it again dead? Now every time I tried it with the tech2 all the icon lights on the dash background lit up but the gauges were dead. So that's got to mean something.

 

ttt --- So SWAG here.

I would check for a loose connection. Maybe around the ODBII connector, but could be anything. Wiggle some wires etc see if It will come back.

 

Sounds to me, (this is my opinion and you know what that means), based on the info you've provided, you have a intermittent low speed serial LAN issue. You are correct as the BCM is the bus master for both the LS GMLAN (low speed serial single wire) and the HS GMLAN (high speed twisted pair wires). GM uses "other" low speed buses as well but these two are the major players. The HS GMLAN has the major controllers on it to start and run the car (they're data intensive and pass a lot of data therefore the high speed). When the button is pressed to start the car the BCM pings the other controllers to wake them up. When the modules respond back (with the expected response) the BCM cranks the car and simultaneously powers up the LS LAN (where the IPC sits) This is noticeable as the needles on the IPC sweeps after the car cranks.

There's a couple Service Bulletins (08-07-30-021G, 08-07-30-021E) that discuss chaffed wires or pushed back pins within these busses. Only issue is these SB's are for 2007-2013 6L80 vettes. I would say since you describe your issue as intermittent this still could pertain to you. I'll also throw in GM's notorious cold solder joint issues along with the chaffed wires or pushed back pins. If you don't have service manuals you can search the interwebs for diagrams of these buses to start your trouble shooting should your issue stop being intermittent. This won't be as easy as cleaning grounds and your issues magically disappear. I've fixed many a bus issues on 08 and above vettes, but haven't had the pleasure to work on a 05. The number of controllers sitting on these busses will change between the years GM made major changes (i.e. the 4L80 has the TCM built into the ECM. The 6L80's have a separate TCM located in the trans itself, another is F55 equipped cars).

Her is a generic diagram for GM buses. I will also point out that the LS GMLAN that you see in the diagram shows it terminating at the DLC (ODBII connector) this is probably the reason your Tech2 can talk to the IPC. FYI if you find the pinout for the ODBII, pin 2 is labeled Class 2 Serial bus. This is the LS GMLAN. Pins 6 + and 14 - are the HS GMLAN's twisted pair.

Good luck!

 

Pull the gage cluster out and check out the wires...there are only 4 screws to remove.

 

The data signal is there I see it on the tech2. What makes everything sweep when you start it.