eMMC MCU1 failure fix and MCU2 upgrade

eMMC MCU1 failure fix and MCU2 upgrade

I have a Model S 75 from December 2017. I’m dreading the moment that my MCU1 stops working and I have to change it, especially if that happens when I’m no longer under warranty (which will happen soon). Lately, my touchscreen has started failing. One day it will reset itself twice, another day it would take forever to calculate a route, and a different time it would erase all of my ‘favorite’ places saved in the navigation system. I took these as signs of the touchscreen going to break soon, so I decided to take it to the Service Center. Here’s all I know about MCU1 failures and short term and long term fixes.

Touchscreen failure symptoms and my experience at the Service Center

As I said, these are the main things that happened:

  • Both IC and MCU were resetting themselves randomly pretty often (2-3 times a week)
  • Favorite addresses got randomly erased one day
  • Navigation is veeeeery slow (more than usual). For music, that’s ok (my kids are less tolerant, tho). For calculating routes, it’s a big pain.
Scheduling the appointment

I first scheduled an appointment with the mobile service. I believe they ran some remote tests and canceled my appointment in order for me to schedule a new visit to the Service Center. I did that. The day I took my Model S in, they were not able to give me an estimate of how long or how much the service would be. After a few hours, I checked in again and they said they’d have to take

Scheduling the appointment
  • Took the car into service on a Friday
  • Called next Monday - they said it wouldn’t be ready at least until Wednesday
  • On Tuesday morning, I received a notification that my car was ready for pickup
Diagnostic and fix

I was a bit disappointed. They didn’t seem to find anything wrong, I am also not completely sure what tests they ran. I had shared with them the exact days and times of the last few error occurrences, so I expected something more specific than this which is what they shared in the invoice:

‘Technician Performed autodiag for MCU and no issues found for MCU. Performed 12v reset and tested function of MCU. MCU is functioning properly. Advise customer to continue to monitor concern for further diagnosis if needed.'

After a week or so of driving the car, all I can say is it’s still resetting itself (it has happened 3 times) but the navigation is faster and I am happy with that. However, I still think my MCU is going to stop working any day now, so I want to be prepared.

A new fix for the MCU1 eMMC failure

Older Model S and Model X versions with MCU1 have a well-known issue with the eMMC (which stands for Multi-Media Card Memory) which causes the touchscreen to stop working. The eMMC has a finite number of writing cycles and that, added to the fact that Tesla is logging a lot of data, has resulted in eventually hitting limits and touchscreens failing. I’ve had my Model S for almost three years, so this is most likely what’s going on with it.

What I think happened when I took my car into service is that they may have deleted some old logs that were taking up a lot of space and that’s the reason why it’s working faster again. But I don’t know for sure because the Tesla technician didn’t describe it like that to me.

It used to be the case that the only way to fix this problem was to replace the whole touchscreen. Just recently, I learned that Tesla has started to fix the issue by only replacing the daughterboard. This operation saves the owner about $1,000.

Fixing or upgrading to MCU2? (And cost)

Assuming your MCU can be fixed, is it worth paying for it, or is better to just upgrade to MCU2? The MCU2 brings new features such as dashcam viewer (for Sentry Mode), new video games, and video streaming services (Netflix, Hulu, etc.) and it’s also way faster (navigation, maps, and browser).

First, I will share my opinion. And then, I will try to break-up the costs (or what I know about those). If you’re going to keep your car, I think upgrading the touchscreen is a great investment. That’s it. It’s just night and day, it’s not a nice-to-have, it’s a 200% improved user experience (plus the new capabilities).

What’s the cost difference? Let’s look at the different options.

  • Fixing the MCU1 replacing the daughterboard costs about $500.
  • Replacing broken MCU1 costs about $1,500.
  • Upgrading from a somehow working MCU1 to MCU2 costs about $2,500.

I’ve tried to find out if you could upgrade from MCU1 to MCU2 when the screen is not working anymore. Here’s what I’ve found:

  • It’s possible but Tesla is asking to cover the cost of both the MCU1 fix ($1,500) and the MCU2 retrofit ($2,500). That would be $4,000 unless you’re still under warranty.
  • The upgrade is not possible (I have been told this over the phone by a Tesla sales representative)

Unfortunately, I don’t have hard evidence of any of those, but I will keep updating this article as I find out more about this topic.

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