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.
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.
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.
If you suspect you have the issue then the course of action depends somewhat on the extent of the failure:
A word about safety. Tesla deem the car ok to drive even with a failed MCU although this is only for short distances. When the MCU is not working there are a number of problems. The airbag warning light will be present on the dash and in many countries this would be a vehicle safety test fail. The turn indicators/repeaters will stop making an audible noise. Access to lights including fog lights will not be possible. These can all cause problems for the driver
Some still question whether this is acceptable especially as these cars have unlimited mileage warranty on the battery and motor, however we think this is a reasonable compromise as it doubles the warranty period which was previously inforce.
Tesla had previously also reduced the cost of the fix should the car be out of warranty. This is now ~$500/£400 which is far better than the previous $2500/£2000 they were charging for a replacement MCU1 (not to be confused with the MCU2 upgrade).
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.
Tesla offer memory board replacement for approx $500/£400 and MCU2 upgrades for approx $2500/£2200 with the radio and extra $400/£400
Alternatively you can get the eMMC memory replaced in the MCU by a 3rd party. We don't feel this is a cost effective option any more and would advise against it.
The final option very much depends on your skills. The old Tesla Hynix memory chip can be removed appropriate equipment, the contents copied across to a new higher grade memory chip such as the eMMC E-MMC MLC EM-20 IND memory chip and then install the new chip. While the process is not exactly DIY, a competent electronics engineer should be able to perform the operation if you can extract the board from the dash. It's not easy but for those with the skills and an out of warranty car it can save money. Details on what needs to be done can be found on DIY Electrical car and a more abridged version on GITHub.
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.