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Discussion Starter · #1 ·
The purpose of this thread is to discuss OnStar, and specifically the OnStar implementation in the GXP, which includes BlueTooth. Please only post in this thread if you wish to have a purely technical discussion about how OnStar works, how Bluetooth works, and how they work together with the other modules in the car. Too many of these threads degenerate into pointless side discussions (or arguments) about "why" one would be interested in these things, and those sideshows really reduce the value of the forum. AF_Don, if this thread belongs in the Stereo/Electronics forum instead, just move it there, but since BlueTooth is not in the GT's I started it here. Onward...

The attached picture shows the OnStar box which is attached to the underside of the trunk roof (under the rear window).

The large white connector is the interconnect to the Stereo, Cabin Microphones, Power, BCM, ECM, and TCM. Yes, it is connected to all of these modules. That is how GM polls the status of the powertrain, brakes, airbags, etc in the monthly report you get from OnStar (if you still have the $ervice enabled). It is possible that the ECM and TCM actually communicate with OnStar via the BCM for commonality among different cars, but I can't find any tech data on this subject.

<<Note that this thread has nothing to do with the data recorder / event monitor - that's a separate box that should be discussed in a separate thread. It's probably on the CAN bus like the rest of these modules, but the logical interfaces are separate and for a separate purpose - separate threads please.>>

Anyway back to OnStar... The black tab is the BlueTooth wireless antenna, and it is on a little coax connector to the box. This is the antenna that talks to the BlueTooth wireless device in your cell phone. Your cell phone uses its own antenna normally, but relays voice & data via a separate wireless BT module in the phone to a BT accessory inside the OnStar module. The OnStar directs it via the white connector to/from the microphone/stereo.

The blue and pink connectors are coaxial. These are the GPS antenna feed (L1-band) and the RF wireless feed that OnStar uses to communicate with the cell network. Does anyone know which is which? The wireless interface between OnStar and the outside world is basically just another cell phone - it is voice and data via cell towers. If anyone knows any details about this service (i.e. does GM buy bandwidth on ATT's towers, or what?), please post that information. The GPS service and the wireless service operate with two completely separate antennas as L1 and cell bands require differing geometries for the antenna. Note that while the GPS receiver is communicating with satellites, the OnStar wireless is just another cell network interface.

If you want to do mods or work on the OnStar box, the fuse that disconnects power to the OnStar box is in the trunk fusebox and it's position F8 - 10 amps. If you remove this fuse, OnStar and Bluetooth both stop functioning until you restore the fuse.

From what I've read, the GPS receivers used by OnStar are actually pretty good. They have ultra-fast acquisition times and are reasonably accurate. It's too bad it's wasted since all you can really do with it is turn by turn nav and emergency response - and those only if you pay :-(

Now for the purpose of the thread: Does anyone have more technical detail on the interaction between the computer modules (ECM, TCM, BCM) and OnStar? What are the logical interfaces between these modules and the OnStar box? Does anyone know how to hack the digital interfaces to OnStar for nav purposes, monitoring purposes, or other fun? Are there any benefits to this? Is there anything in these interfaces that you can't get by just plugging a CAN bus monitor into the OBD2 port? Schematics, wiring diagrams, any tech data that's public would be of great use and spark some interesting discussions I'm sure.

Thanks in advance!
 

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Great thread starter. There A LOT of other good discussions on this in the forum.

OnStar contracts with Verizon for cell service. If you have a Verizon account for your mobile phone, you should be able to combine the number for the car into your account, and use minutes from your normal plan instead of buying OnStar minutes. You USED to be able to do this...not sure if they still will allow you to do it. I never tried because I've always been an AT&T customer.

I attached the diagram for the box, but it doesn't show which cable is which. I'll keep looking. It also doesn't show the BT antenna.

Great pic you took though, and I am going to check mine to see if the BT antenna is messed up or loose...

 

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Discussion Starter · #3 ·
Schematic

Thanks, BigZub. This is exactly the kind of data I was hoping for. No BT function shown though so it must be a rev of the VCIM that is not in the GXP. Recommendations on where to find more of this kind of info?
 
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