Hi guys so I'm in a bit of a rough spot, looking for some advise.

I was driving to get dinner last night with the AC on and all is fine. I Turn the ventilated seats on and immediately the AC air turns hot and the AC and Seat buttons are frozen and not operational. I pull in the parking lot and as I'm pulling in the parking lot to park i get all these error messages on the DIC. ( Service Theft System, Service Tire Monitoring System, Service Air bag System). I shut the car off and everything turns off, the A8 Transmission lights that show you what gear your in went dark, the instrument panel went dark. The AC controls and radio still worked. The doors didn't work i had to use the emergency door release to get out.

I disconnected the battery for 20 Minutes and that didn't fix anything. I had a buddy of mine meet me to give me a jump. That helped a bit with the electronics as i now could put the car in gear and the DIC came back on with all the same warning lights. I took the battery to my local Auto store and had it checked. They said it was good but needed to be charged. The battery is 5 years old so i bought a new one. Installed it and nothing changed the same.

The key also has to be in the steering wheel fob location for me to even get the car in accessory mode. The doors don't want to open, sometimes they will. I was able to remote start the car twice but when i get in the car and press the igniting nothing happens. Remote start is not working anymore. I did get the car to start 1 time but it immediately died.

I have added the NAV Tool a year ago with no issues, I'm wondering if that failed. I"m at a loss of words. I have an appointment set up for Monday. I have check all fuses and they all look fine. Car tries to turn over and then nothing.

 

Sounds like you had/have two problems. Your main battery sounds like it went bad. The doors opening trouble is also a sign that your FOB batteries are also bad. Change out both FOB batteries. To be clear, you can start the car with the FOB in the steering column slot, correct?



Elmer

 

No the car will not start at all. It tries to turn over but nothing. I have to have the key in the fob location spot to even get the car in accessory mode. I just changed batteries in both of my keys and the same result nothing. When i try to lock the car i don't get that chime alert that its locked. When I'm in the car i have to use the emergency release to get out. The doors wont work to get out. I can get in the car with the key fob by pressing the unlock button like 5 times. I just replaced the battery with a new one so the battery is brand new.

 

The first thing id try is disconnect the new battery for a few hours and be sure its connected back properly. Not sure if youre familiar but the connections are finicky.

 

OK, tow truck and dealer time. You have a chunk of electronics fizzleing out. I would guess the BCM.


Elmer

 

Okay Figured it out. The Onstar mirror does not come on. When i hold the harness behind the Mirror all the lights turn off and the car starts right away. As soon as i let go the Onstar lights on the mirror turn off and turns the car off and starts throwing all the service light. I unplugged the mirror and now everything works fine and no issues. I just don't know if its the harness on the mirrors side or the headliner side.

Can i just buy both harness at the dealer or do i have to buy a whole new mirror.

 

OP - there have been other threads where the Onstar mirror connection caused elec issues across the entire car.

 

Scary Situation I'm glad i figured it out and it shouldn't be a crazy expensive fix.

 

Interesting...I have been reading here for about 1.5 years and first I heard of the onstar mirror not working causing other issues. Good to know and good job troubleshooting.

 

How the hell did you find that? Good job.

 

Yes very interesting. I don't believe Gm should allow a faulty on star harness to cause so much electrical issues with the car.

 

have you tryed just disconnecting the mirror,or pulling the onstar fuse,,then seeing if the car runs?

 

Well i tried to start the car again and it started but it shut off immediately and i just happened to look at the rear view mirror and noticed that the mirror was not lighting up like it always does. I saw a youtube video on a guy who has the new C8 and his on-star mirror was not working either and he was getting some weird issues. So i noticed when i held the harness on the rear view mirror the onstar lights came on and all the error messages went away and the car would start and stay running but as soon as i let go of the harness the car would die and all the error messages popped up again. So i disconnected the harness and now everything works like normal no issues what so ever.

I dont know if its the harness from the rear view mirror or the harness that comes down from the header trim piece that connects to the rear view mirror.

Hopefully i can just buy the harness separately.

 

yes disconnecting the mirror fixed the issue, when i plug it back in the issue comes back. I dont know if the issue is on the mirror side or the head liner harness side. Its a harness problem because when i hold the harness the onstar starts to work again correctly but as soon as i let go the issues happen again.

 

Wow, learn something new everyday.

Glad you diagnosed it!

 

Holy crap. Lucky you found it. That could have gone on a long time.

 

My '17 GS had this issue within the first 1000 miles, i'm the second owner, the original owner let me know this.

 

I can only imagine what would have happened if you took it to a dealer for a diagnosis. It could have (not necessarily) been very costly by ruling out everything the DIC flagged.

 

what did you change to fix it?

 

well the dealer charges a flat rate to diagnose I thought Around $175 but I think it would have been there for several days