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Like all cell phones, the OnStar has GPS. But it doesn't necessarily talk to the on board computer. And it certainly doesn't talk to a navigation device. If the OnStar GPS communicated with the rest of the vehicle, you would never have to set a clock.
The Onstar unit is attached to the CAN bus, and most certainly talks to the other modules in the vehicle. The folks at Onstar can ascertain your speed, unlock your vehicle, be alerted when you crash, and probably have access to anything piece digital information they want that the vehicle monitors. The Onstar unit is directly connected to the GPS antenna (the shark fin on top) and it is the device that calculates your location. It then broadcasts the GPS coordinates on the CAN bus. If you have navigation head unit, which is also on the data bus, then it picks up these coordinates, shows you where you are, provides directions etc.
Strangely, I don't think the vehicle clocks sets its time to GPS time. It should.
You don't have to take my word for it. Look at the schematics.
Last edited by mountainmanjoe; Jul 21, 2019 at 8:01 PM.
Then why can't I access the GPS through my ELM 327 device? The PID is there to read speed from GPS, but it doesn't read it. BTW, the schematic does show the CAN bus, but doesn't specify what data is sent through it.
As for locating you during an E911 call to OnStar, the data is sent exactly like any other cell phone made after the late 90s does. And yes, it does use it's own GPS antenna, just like a cell phone. This is standardized by law, because when you're not a OnStar subscriber, the phone is required by law to be able to call local 911 call centers (also, like any cell phone, not subscribed to any service). To do anything in a non standard way makes no sense.
Then why can't I access the GPS through my ELM 327 device?
Ahhh, because GM doesn't want you knowing what it is. GPS coordinates are not part of the OBD system so there is no PID for it. Thing of this nature (non engine related) are transmitted on the GMLAN bus. GMLAN specifications are NOT available to the general public, and your ELM reader isn't even connected to it! (Pin 1 on the DLC). It's all trade secret stuff. But that hasn't stopped people from hacking it. Not many people care, though, because everyone uses their smartphone or aftermarket head unit which comes with its own GPS receiver.
Originally Posted by StanVan
The PID is there to read speed from GPS, but it doesn't read it.
Just because a PID exists, it doesn't mean your particular vehicle supports it. There are probably hundreds of PIDs that won't work on our vans. Remember, vans are like the ginger stepchildren in the GM family. Also, the Onstar unit (or "Telematics Communication Interface Control Module" as its referred to in tech docs) only provides coordinates. GPS speed requires calculating distance travelled, so that information might actually be provided by nav head units.
Originally Posted by StanVan
As for locating you during an E911 call to OnStar, the data is sent exactly like any other cell phone made after the late 90s does.
I'm sure you're right. They COULD use cellular tower triangulation. But Onstar has access to your GPS location, so why not use that. It's more accurate anyway.
Originally Posted by StanVan
And yes, it does use it's own GPS antenna, just like a cell phone. This is standardized by law, because when you're not a OnStar subscriber, the phone is required by law to be able to call local 911 call centers (also, like any cell phone, not subscribed to any service). To do anything in a non standard way makes no sense.
I don't understand. What has its own GPS antenna and what does it have to do with calling 911?
Last edited by mountainmanjoe; Jul 22, 2019 at 1:33 AM.
Each and every cell tower uses GPS to synchronize the handoff when you are on a call and travel from one cell tower to another. Your cell phone uses this data to set your clock only, every time you answer a call There is no "triangulation" done by a cell phone or tower. Cell phones have their own GPS. It came about by work done by the CTIA and APCO, to enable 911 call centers to find a caller in an emergency when he/she may not be able to talk. All cell phones made since the late 90s have GPS built in to them. The sad part is that while the cell phone industry has done this, many 911 call centers have not procured the equipment to read them, citing costs as the reason. A call center in a major city can find you, but in a rural setting, maybe 50/50.
But to your first point, why would GM hide info from being in the OBD? And if they're hiding stuff, why not hide everything not drive train related? Certainly speed isn't information needed to diagnose an issue, yet Torque reads it. RPM isn't important in that if an issue happens at a certain RPM, the computer doesn't record that. In fact, the computer only stores the codes determined by the individual inputs, and doesn't use multiple sources of data to come to any type of conclusion, so why not hide that data?
