Tesla MCU1 eMMC failure

On Feb 1st, 2021 Tesla decided to recall all cars with the MCU1 and pro-actively fix the eMMC issue with this hardware. This was after many complaints and private prosecutions by owners and we suspect more importantly by intervention from the NHTSA (US Safety board) who gave Tesla an ultimatum to do it voluntarily or be compelled to do it. Approx 135k cars will fall under this recall.

This is finally good news and can bring closure to this significant problem that has blighted many owners enjoyment of their cars. It sadly will not provide redress to those that sold up or paid for the MCU 2 upgrade at considerable expense looking to simply avoid being left stranded by the failed MCU. We are leaving the original details below as a reminder to some of the background and attitude of Tesla over a number of years.

If you have not been contacted by Tesla regarding the recall, then in the coming months we suggest you make proactive contact with them to arrange for the recall to be performed at a time convenient to yourself.

The Tesla Media Control Unit or MCU has been a significant feature of the cars since the Model S was first introduced. The original version is now referred to as MCU1 was updated in 2018 and is different again in the Model 3. Unfortunately, Tesla chose to make two mistakes which hurt the MCU1 badly, firstly they used cheap embedded Multi-Media-Card memory (abbreviated to eMMC) which has a finite number of write cycles, and secondly they left on excessive data logging that wrote to this memory. As a result the memory is constantly being over written and as a result will eventually hit the write limit and fail.

Tesla previously responded by adjusting the amount of logging the car performs. This however does not prevent the issue as many activities write to this memory including streaming music and while the reduced logging extends the time before the inevitable failure, this is actually a slightly cynical move pushing more of the failures to occur outside warranty. Tesla have now accepted the problem and have extended the warranty on the MCU1 eMMC issue to 8 years and 100k miles, whichever comes first, from date of first customer delivery.

What are the symptoms?

The most noticeable symptoms on the lead up to a permanent failure are:

Our guide to rebooting your Tesla talks through some other potential causes of the MCU crashing or rebooting which are worth exploring before jumping to the conclusion that your MCU is about to fail, although increasingly we feel even those issues are likely to be linked to the eMMC issue.

Do you have an MCU1 with the potential problem?

Autopilot 1 and MCU 1

To determine the version of MCU in you car, the easiest way is to go the Software menu and then click on the "Additional vehicle information" text. A pop up will appear.

If the details presented indicate the NVIDIA Infotainment system as shown in this example, the car has the MCU1.

The good news is, Tesla now seem to have updated their software to notify you if the car suspects the MCU is failing. If you get this warning then contact the service centre. If you don't get the warning and still suspect you have the issue then the course of action depends somewhat on the extent of the failure:

Remedy while under the revised warranty

Tesla now accepts that there is a problem with the memory on the eMMC for MCU1 cars which were built before March 2018. As a result they have extended the warranty of the eMMC memory to 8 years and 100k miles, which ever comes sooner.

Some still question whether this is acceptable and Tesla may well be forced to perform a recall at some point.

An out of warranty fix is approximately $500/£400

It should be noted that the extended warranty is only for the eMMC memory board and other failures have the original warranty and it is unclear whether corruption to the memory due to a partial failure is covered or whether Tesla will want to charge. We suspect Tesla will need to cover these issues.

Remedy outside of the revised warranty

Tesla offer memory board replacement for approx $500/£400 and MCU2 upgrades for approx $2500/£2200 with the radio and extra $400/£400. Third parties did offer fixes but these were generally more expensive that the Tesla option and came about because Tesla at one point wanted over $2000 to fix a failed MCU1.

Upgrade to MCU2

If you are in the unfortunate position of being out of warranty with an MCU1 failure, you can consider a MCU2 upgrade. Tesla have reduced the price of this to circa $1500/£1400 and offers more functionality. Personally we would only suggest this for cars with Tesla autopilot hardware and not the older AP1 system as the extra features are somewhat limited with AP1.

Removing Pin to Drive with a dead MCU

If you have pin to drive enabled and the MCU dies there is no way to enter the pin code which would ordinarily leave you unable to drive the car. There is a temporary fix to get you home or to a service centre. Disconnect the 12v battery for a short period of time and reconnect. You should find the car can then be driven. This is not a security bypass as if the MCU fires back up the P2D will be enabled automatically, it only works with a dead MCU.

Note: the ability for the car to charge can be compromised with a dead MCU and therefore this is only a temporary step to get you home, drive the car onto a low loader or a short trip to a service centre.

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