Service Mode disables your ability to see location in the Tesla app, but it doesn't actually disable GPS location through the API. When I'm in service mode I can still see the car move through 3rd party services (TeslaFi, Tessie, etc) so I know they've actually moved it into the shop and are getting ready to work on it. For example, moving from the lot in front of the Houston North service center into the facility (definitely in service mode at this point as I'd checked several times in the app).
Edit - I'm actually pretty sure it's only the Tesla app that is altering behavior based on In_Service flag or whatever. I don't think anything is limited at the API level. I didn't want to honk my horn or anything annoying, but all the controls on third party services still seem to function. I tried turning on climate when the car was still in the front of the parking lot, and it appeared to work and I saw the cabin temp reduce for the minute or two I left it on.
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