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3G connection problems after MCU replacement

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I done quite a bit of searching in the forums here and via Google, but haven't found mention of this.

Recently, the Bluetooth in my Model S P85D started having problems which gradually became worse and worse. Tesla Service eventually decided that the only solution was to replace the MCU. After having my MCU replaced, I now find that my car often takes several minutes minutes or more to connect to 3G service, including right near my house when I drive away from my WiFi. It's never had this problem before. And it means when I hop in the car and want to navigate somewhere, I may have to to wait for several minutes before 3G connects to use the car's nav.

So, as it happens, I also now see that I made some huge mistakes by not researching this more thoroughly before letting them fix it.

Where I made my first mistake: I didn't know there was a 3G to 4G upgrade. Could I have asked for this at a discount since almost all of the labor and probably most of the parts would be included in my in-warranty MCU replacement?

Second big mistake: They told me there would be a delay in servicing the car to order the an MCU, so they offered to cancel my service appointment and reschedule when the MCU came in. Then they called back and said that another customer had said they wouldn't be scheduling their MCU repair appointment any time soon, and the MCU they had on had for that repair, they could use for mine. So my appointment was back on. Why was this a mistake? I'm fairly certain the other customer had seen that new MCUs come with the faster Intel chip and so declined to schedule their previously planned MCU replacement, hoping to wait for a new Intel unit. So now I have another Tegra-based slow-poke unit with slow 3G.

By the way, here's the strange thing: My service order contains the phrase, "Perform LTE Retrofit On MCU With Gyro Board" but I did not end up with 4G in my car. From what I have read in my belated research, there's a second piece of the service to swap from 3G to 4G; an "LTE" version of the MCU is not sufficient to magically get you 4G service.

Now, those huge mistakes aside, it would be OK if it weren't for the fact that my 3G is having this problems connecting. I'll have to see if the problems persist.

Anyone else have any experience with LTE MCUs having trouble connecting in 3G mode (and can't gonnect in 4G mode because don't have the 4G upgrade)?
I wonder if this could be unrelated to your MCU swap, since in recent days I've also experienced really slow 3G connection times. It seemed inconsistent, and I tried rebooting multiple times while driving, which didn't seem to help.

I called service, and they asked me to try rebooting while the car is parked since that's apparently a more thorough reboot (press brake pedal while holding down both scroll wheels). Now that I've tried this multiple times, I can now say that it consistently takes my car 7 minutes to connect via 3G, from a cold start or reboot.

Connectivity shouldn't be a problem. Takes the same 7 minutes in Sunnyvale or Cupertino.