It sounds like the car's LTE (cellular) connection is poor or non-existent; however, to be sure, I suggest performing a series of experiments to fill out a 2x2 matrix of the phone and the car on WiFi vs. LTE. That is:
- Phone on WiFi, car on WiFi
- Phone on WiFi, car on LTE
- Phone on LTE, car on WiFi
- Phone on LTE, car on LTE
Activating WiFi normally causes it to take priority over LTE, and LTE should be active by default, so you shouldn't need to explicitly enable it. (LTE
can be disabled for phones in various ways, but you shouldn't need to do so for this test.) For each condition, wait a minute or two after disabling or enabling the connection to give the device a chance to bring up its connection, then test the app. Also, test the car's ability to access network data in the form of a streaming music service or its built-in Web browser.
If my initial hypothesis is correct, then everything should work fine with the car on WiFi, no matter how the phone is connected; but when the car is on LTE only, both your phone app and the car's data features will stop working, or possibly work but be sluggish or otherwise unreliable. If you see another pattern, then that will pretty much nix my hypothesis, and the pattern you observe may provide a clue about what's going on.
If my hypothesis is correct, then contact Tesla with the results. It's conceivable that it's a simple matter of the account Tesla has with AT&T (I
think that's who provides the Tesla LTE account, but I'm not 100% positive of that) being improperly set up, which could be fixed remotely. If the hardware is bad, then it will need to be replaced.
If the cause is something else, then I'm less sure of what the solution would entail. It could be a simple thing that Tesla (or your cell phone carrier) could fix remotely; or it might require a Tesla service visit or something else, like cleaning malware off a phone or reconfiguring firewall rules on the phone.
Another experiment you might try is to leave your Tesla connected to your WiFi network and then connect your phone to another WiFi network (at a neighbor's house, say; or drive another car to a Starbucks or whatnot with free WiFi). If that works, then it indicates some sort of problem with the LTE network, like firewall rules (on your phone, on your cellphone provider's network, or on Tesla's servers) that are blocking the connection.
