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 of 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 have partially responded to adjust the amount of logging although this just extends the time before inevitable failure and the MCU2 has a larger memory which means the frequency of overwriting the same part of memory is redeuced, also extending the time before failure.
The most noticeable symptoms are an increase in MCU rogue reboots/crashes on the lead up to a permanent failure, or a significant slowing down of the MCU in operation. Our guide to rebooting your Tesla talks through some other potential causes of the MCU crashing or rebooting and it is worth exploring these first before jumping to the conclusion that your MCU is about to fail.
You may also need to determine the version of MCU in you car. The easiest way is to see if the car has Tesla Theatre, Caraoke, Pole position or Cuphead entertainment options, these are only present in MCU2 cars and model 3, and not present on the cars with MCU1. That said, the problem can still occur in all cars.
If you suspect you have the issue then the course of action depends somewhat on the extent of the failure:
Tesla are aware of the problem and it is believed they can interrogate the car which will tell them how far through the number of safe writes it can do before symptoms of failure can be expected. Their opening response however is typically a quotation for the diagnostic work in the event they do not believe it is a warranty matter.
In the event of a problem being found. Tesla will, at their discretion, replace the whole MCU on a like for like basis should the problems met their failure criteria. However, Tesla seem to expect owners to tolerate a number of MCU crashes before deeming it a warranty matter. Tesla will also only consider replacing the MCU during the 4 years, 50k mile warranty period. If the car falls outside this period, Tesla deem it a non warranty repair and replacement costs are current;y circa £2500/$3000/€3000.
The problem has been clearly established as a design issue and as a result local consumer law may be applicable depending onm your country. Tesla have so far resisted people applying their consumer rights. For owners that feel they need to escalate, Tesla's warranty documentation suggests writing to them formally at one of the following:
If outside warranty then applying your local consumer protection legislation is an option. The extent the car is outside warranty will have some influence on the likelihood of success. For example an owner with a 7 year old car and 200k miles may find any court proceeding to be less favourable than an owner only a few months outside the 4 year warranty window especially with low miles. We strongly suggest you take local advice if you wish to go down this route and many car insurance policies have legal protection included which may be a suitable mechanism.
The final option is to have the memory replaced in the MCU with a version that is fit for purpose and is unlikely to fail in the future. It should be noted that the replacement of memory will almost certainly invalidate any future claim with respect to the MCU.
Companies that offer this service, which can cost between 1/6 and 1/4 of a new MCU are listed below and are based on other owners recommendations. We understand the memory contains key information that needs to be extracted and reloaded onto the new memory and therefore can only be done of the MCU is in a partially serviceable state.