Tesla MCU1 eMMC failure

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 by adjusting the amount of logging the car performs. This 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. The MCU2 has a larger memory which means the frequency of overwriting the same part of memory is reduced, also extending the time further before failure.

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.

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:

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

Tesla's typical response and your rights

Tesla's first response is increasingly an attempt to perform a temporary fix to deal with the consequences of a failure. This is typically itemised as '12V reset, offline firmware update, configuration of media chip carried out', all for under £100/$100. This is in effect just dealing with the corruption of the memory that has failed and how the memory is partitioned, this has not solved the underlying issue of failing memory.

In the event of the above not fixing the issue, Tesla will, at their discretion, replace the whole MCU on a like for like basis. They have now also started to replace just the faulty sub assembly with the memory chip on which is considerably cheaper.

However, Tesla seem to expect owners to tolerate a number of MCU crashes before deeming it a warranty matter so unless there is a significant failing of the MCU, Tesla will often try to charge a diagnostic fee and advise the owner there is within tolerance. Tesla will also only consider replacing the MCU under warranty during the 4 years, 50k mile warranty period even though this is a well documented design issue.

If the MCU falls outside warranty due to the eMMC, the repair cost at Tesla has steadily fallen from $2000 to $1000 and now they are starting to offer just a replacement memory board for under $350. While there is still an argument this is a design defect, the repair cost is becoming more realistic.

Remedy outside of warranty

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.

As an aside, it is worth noting that in some countries, there is no mileage limitation on the warranty within the first 2 years irrespective of Tesla's warranty documentation. High mileage cars Tesla claim to be limited on miles but within that time still have a legal right to have any appropriate matter dealt with as if under warranty. You may need to argue this case as Tesla are generally unwilling to accept this.

The specific problem has been clearly established as a design issue and as a result local consumer law may be applicable depending on your country. Tesla have so far resisted people applying their consumer rights. In the first instance you should always formally raise with Tesla as this will strengthen any legal proceedings you subsequently take if they are still unwilling to repair free of charge and their explanation is not satisfactory.

Vehicles registered in the U.S.:
Tesla, Inc.
Attention: New Vehicle Limited Warranty
P.O. Box 15430
Fremont, CA 94539

Vehicles registered in Canada:
Tesla Motors Canada ULC
1325 Lawrence Ave East
Toronto, ON M3A 1C6
Attention: Vehicle Service

Vehicles registered in Europe:
Tesla Motors Netherlands B.V.
Atlasstraat 7-9, 5047 RG
Tilburg, Netherlands
Attention: Vehicle Service

Include the following information:

In the very likely event that Tesla will simply ignore such correspondence, and certainly not respond in good time if you car is broken, then you may be forced to have the car fixed, pay the money but make it clear this is under dispute, and commence legal proceedings after you have formally raised the matter with Tesla giving them the opportunity to remedy.

If you are outside warranty and feel you may have a case under local consumer law then we suggest you take advice.

In many countries there is free consumer advice support from organisations such as Citizens Advice Bureau in the UK, State Consumer Protection Offices in the US and similar bodies in other countries.

It is also worth remembering many car insurance policies have legal protection and cover, and they may be prepared to represent you, their costs covered by your insurance and typically by Tesla if the they win a case.

Finally, many law firms offer a free initial consultation especially those that operate on a no win - no fee basis. Whether they will represent you on such a case will vary from law firm to law firm.

Tesla are also offering MCU2 upgrades for approx $2500 although the availability varies from country to country, as of July 2020, only owners in the America market can order these.

Alternatively you can get the memory replaced in the MCU by a 3rd party. It should be noted that the replacement of the memory will almost certainly invalidate any future claim with respect to the MCU although we know of some people who have taken Tesla to court and claimed the 3rd party costs and have won (although by default as Tesla did not defend the claim).

Companies that offer this service, which can cost between $500 and $900 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 if the MCU is in a partially serviceable state. You pay for skilled work, however it should also be noted that the procedure takes approx 2 hours unless extracting the data from the old memory is a challenge. We feel the hourly rate is therefore VERY high and this should start to reduce as Tesla now provide a refurbished MCU with 2 year warranty for only a few hundred $ more.

Given Tesla's revised pricing which is cheaper than any 3rd party solution, and it has warranty, we can not recommend any of the following options except in exceptional cases where Tesla can not repair the car in a reasonable time frame and you are in desperate need of an urgent remedy.

The final option very much depends on your skills or whether you know someone with the 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 DIY, any competent electronics engineer should be able to perform the operation if you can find a car mechanic to extract the board from the dash. Its not easy and some will prefer to pay the price of others to do the work, but the costs can be significantly less. Details on what needs to be done can be found on DIY Electrical car and a more abridged version on GITHub.

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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