MCU Failures

MCU Failures

Is anyone tracking MCU failures like they are tracking Updates? It would be really interesting to know how many MCUs have failed. What age they failed at, years and miles? What was the cause of the failure, i.e. was it the logging memory chip?

I suspect Tesla knows but probably would not tell us.

Also I wonder how many FSD cars were purchased along with how many are MCU 1, AP 2.0, 2.5 and 3. | February 5, 2020

There have been a few dozen reports in the forums, but no way to know the actual number. Let's say there are 10 times that amount that has failed - 250 units.

About 330,000 model S and X were made with MCU1.

So the failure rate is 250/330,000 = 0.075%, a fairly small number over 8 years, although some MCUs are newer than others.

We have no data on the nature of the failure, as that's internal to Tesla. The memory chip that seems to fail on some MCUs is used for storing the software code, settings, logs, and other information. I did an analysis in another thread that shows the logging is unlikely to cause the failure of the chip, despite many unknowingly saying logging was the cause. With all the new features added over the years, and especially AP, it may push the chip to its limits and cause some early failures. Failure causes are mostly conjecture so be cautious about coming to any specific conclusion.

miked | February 5, 2020

Put me on that MCU failure list. Model S 85d built Nov 2015. 68k miles. Just out of warranty I’m told. Repair cost to be $3k

jordanrichard | February 5, 2020

10 people could have a failure, but 110 people talk about it and the problem magically becomes bigger than 10.......

I understand what the OP’s intentions are, but this is yet another thread about this which just leads into my example above.

Pungoteague_Dave | February 5, 2020

Um, no actually, the engineering problem has been figured out in detail, and there are people who have entire businesses replacing the chip - so way more than 250. It is apparently a design issue that will affect all Teslas once they hit the magic read/write number. And the number of reported failures is way more than a few dozen. My ranger (now friend) says this will affect all pre-Raven/3) Teslas, no exceptions, it is a ticking time bomb - as BH has reported, not generally fatal to travel, but inconvenient as hell. It can't be a forced safety recall because the cars remain generally driveable, albeit with crippled functionality. Tesla needs to start owning this. My sense is that if they make it a priority, the cost should not be too much.

Bighorn | February 5, 2020

Mine made it 283k miles with tons of MCU input

1LuckyGuy | February 5, 2020

MAJOR issue tonight. Wife was driving the 2013 S with 175k miles. Screen resets are slow to reboot usually but they always work. Today, it froze while driving, did the usual scroll wheels reboot, and nothing. AC stayed on, no access to anything. Got home, parked, went out a couple hours later, 20 miles gone, and AC/FAN is still blowing. Tried the resets, numerous times, and even pulled the #51 fuse. The fuse pull stopped the fan... but screen still won't come on. So did I get a full MCU failure? Any ideas? Thanks all. Will repost this in main board for more answers.

jordanrichard | February 6, 2020

PD, wasn’t dismissing anything. I am merely pointing out that affect of a lot of people talking about a single problem. BTW what is the magic limit? What is considered a “read/write”?

jordanrichard | February 6, 2020

BH said his lasted 283,000 miles. For the average driver that’s 18.8 years of driving. I assume these “read/writes” happen when the car is in use and OTA updates. | February 6, 2020

Not sure I'd call it a ticking time bomb. Yes, it will fail someday. So will the battery, tires, motors and just about everything else in the car or any other car. On any given part failure, some people may get 50K miles and some 300K miles or more. I'm not aware of Tesla offering a lifetime warranty on the car.

As for the number of failures, let's take a WAG it's 10 times my first estimate or 2,500 units. That's a 0.75% failure rate. Still fairly low over 8 years of production. Still, it sucks when any expensive part fails, but I don't see Tesla providing replacements for free out of warranty.

jordanrichard | February 6, 2020

Any ICE has a head gasket or two ( V6, V8, V10, V12) that may very well let go and that is not exactly a $200 job......

I know someone who had a boss that owned an Audi L8. It was $1,500 just to replace the thermostat due to everything that needed to be removed and re-assembled.

brdinjd | February 6, 2020

Just paid $2933 for my obligatory MCU replacement today. 2015 85D. Just out of warranty (of course). I suspect my story is (or will be) as common as it is frustrating. I do feel this issue should be on the level of recall since it is actually caused by overactive use by Tesla (e.g. logging) for their own purposes.

1LuckyGuy | February 6, 2020

Does anyone know if Tesla will install a privately purchased MCU? And if you did get one installed from a private mechanic, does it completely screw up the car? In other words, if I bought one on Ebay, would it come up in my car as the car it came from? Or will Tesla program it?

tes-s | February 7, 2020

MCU got replaced under warranty due to a screen issue (a line of pixels went out). Current MCU has about 150k miles/6 years and needs out-of-warranty replacement.

s.grot | February 7, 2020

I believe there is a setting where you can decline sharing driving data with Tesla; perhaps that will reduce the read/writes

steveb | February 7, 2020

2015 85D Mine failed in June of 2019, at around 72,000 miles. $2400
It was the memory that went bad/corrupted. So sad that a $70k+ car needs this kind of work after 4 years. I really don't care about comparing ice cars; I didn't purchase one, so why should I feel better about comparing repair costs? Maybe we start comparing repair costs to the few other EV vehicles.

Anthony J. Parisio | February 7, 2020

Did they give you an MCU1 or an MCU2?

Bill_75D | February 7, 2020

$100 says they gave him MCU1

barrykmd | February 7, 2020

Bill - your bet isn't big enough :-)

steveb | February 7, 2020

Yes, MCU1. At the time (June 2019), SC said I could not upgrade to MCU2. "Tesla" wasn't doing them.

Silver2K | February 7, 2020

2 friends replaced their MCU1 recently for $2200 each. One of them had 130k miles and the other 225k miles.


You must have had something else done, because MCU1 prices don't vary from state to state. I just contacted my mobile tech and was told it's the same price across the country unless something else needed to be done to the car.

Silver2K | February 7, 2020

steveb | February 7, 2020
2015 85D Mine failed in June of 2019, at around 72,000 miles. $2400
It was the memory that went bad/corrupted. So sad that a $70k+ car needs this kind of work after 4 years. I really don't care about comparing ice cars; I didn't purchase one, so why should I feel better about comparing repair costs? Maybe we start comparing repair costs to the few other EV vehicles.

I don't have issues comparing to other EV vehicles. the Nissan leaf a friend (also owns an 85d) owns had to replace his suspension system for 2500 @ 55k miles and he's also down on his range by 40%. He the got quoted over $2k to replace his charge port a few miles later.

Silver2K | February 7, 2020

PS: I have 239k miles on my car and spent only $2,600 out of pocket to repair my car out of warranty.

repairs include:

steering u-joint (combined with rear toe links) $962
rear toe links
1 front air shock $883
parking brakes (I did that myself) $500 for parts
1 tie rods - $216
wiper pump $38

I've saved tons driving my car and would not bitch at all if the screen failed like my friend did daily!

Silver2K | February 7, 2020

2 tie rods

billUK | February 8, 2020

Mine failed at 3 years and 35000 miles, the centre console just cycled. I was unable to enter a PIN to drive so it was a case of the car being taken away on a low loader

jesssstuckey | February 8, 2020

Failed and was pure torture to diagnose and replace. Told my wife would be ok to drive with no center screen and supercharging would still work. She ended up stuck and waiting for a tow turning an already expensive repair approx $2200 into pure hell. I believe Tesla knows all computers will fail with time and need replaced. Feels like it should have been covered by Tesla as the problem of too much data was created by Tesla. Was quoted 4000 to fix a headlight issue, then with discussion price came down to 2000, then 900, replaced off ebay for 135 in parts and $100 in labor at local shop and also got tires rotated for free instead of $500 I was quoted to rotate tires by Tesla.

jordanrichard | February 8, 2020

And all ICE makers know that head gaskets will eventually fail and yet you are on your own once out of warranty.

Want to guess how much a new dual overhead cam head will cost if it was found to be warped............?

Ruby110 | February 8, 2020

Any idea if pre-autopilot MCU1’s last longer? Less data logging?

murphyS90D | February 8, 2020

It's the Linux operating system that does the logging so I doubt that is the case.

Silver2K | February 8, 2020

jordanrichard | February 8, 2020
And all ICE makers know that head gaskets will eventually fail and yet you are on your own once out of warranty.

Want to guess how much a new dual overhead cam head will cost if it was found to be warped............?
---------- a comparable vehicle like an Audi a8, panamera, 7 series bmw or s class Mercedes?

Darthamerica | February 8, 2020

Whoops... There goes the fuel savings! This should be a recall repair considering Tesla wouldn't be Telsa without the early adopters who are on borrowed time with MCU1.

Tldickerson | February 8, 2020

If Tesla swapped out the bad chip themselves they could swap the MCU1's for customers with their own refurbished MCU1's at a very reasonable price. Customers would gladly take a factory refurbished unit over a new one.

tes-s | February 8, 2020

Refurburished is what you get.

Tldickerson | February 8, 2020

@tes-s, our you kidding me! They sell you a refurbished MCU1 for $1,200 ? Wow, that crazy if your correct. | February 8, 2020

@Tldickerson - News flash - they are using refurbished units already. I got the sense MCU1 is out of production and no new ones are being made. It's not entirely clear if some of the chips used, such as the Nvidea CPU is even being made anymore. It hasn't shown up on the Nvidia website for a year or two now. Remember, this was designed back in the 2009-2010 time frame, with chips designed before that. Ten years is an eternity in the high-end chip space, although Tesla could have stockpiled chips/boards or even entire MCU1s before going out of production.

I was sort of hoping MCU2 would be the replacement at some point with a retrofit.

@Ruby110 - Linux data logging uses a trivial amount of memory. I think it's a red herring, but others disagree. My conjecture is all the new features, and perhaps AP, in particular, uses a lot more data at a higher frequency of writes and may contribute to some of the MCU1 failures. While most of the AP process is done with a separate processor and memory, some data is funneled to the MCU1, including some images and videos.

Without a lot of statistical analysis - exact model year, miles, hours, and features used, it's very hard to know exactly the cause or the likelihood of occurrence.

Bighorn | February 8, 2020

With my replacement MCU, car works better than ever and without the gremlins I’ve been encountering for years. A 2% maintenance cost on a car that could have circled the globe 11 times doesn’t seem so bad. Especially when you talk to someone with a boat.

rxlawdude | February 8, 2020

@Big, are you riffing on the maxim, "there are two happy days in a boat owner's life - the day you get it and the day you sell it?"

BarryQ | February 8, 2020

@jesssstuckey $500 to rotate tires? Bullshit!

Bighorn | February 8, 2020

Not really, but I think I remember the conventional wisdom being that you can expect to spend 10% a year maintaining a boat.

Ruby110 | February 8, 2020

@TT and others: Thanks.

jordanrichard | February 8, 2020

I am not a computer expert and through all of these threads about MCU failures and chip talk, no where I have read when does/causes a “write” to happen. Does this happen with the car sitting or driving? If it is related to driving, then wouldn’t it be related to miles versus time?

tes-s | February 8, 2020

I understand the eMMC is used for data logging, storing firmware downloads, and perhaps browser cache. It is supposed to rotate blocks so they are all reused equally, though if there is static data that would not get reused.

Seems like a pretty high MCU1 failure rate to me - hopefully fixed in newer MCU revisions.

jordanrichard | February 8, 2020

I know what downloads are and browser cashe. I also understand what logging is, but what data is being logged? Again though, if the logging is associated with miles driven, then this puts this into a different context. Bighorn’s MCU lasted the equivalent of 18 years of the typical driving. | February 8, 2020

@ jordanrichard - Likely more writes are occurring when driving, but with Sentry mode on, MCU1 is powered and the car is processing video. If you have HW2.5 it is saving that video to the USB, but it's unlikely much, if any, is going through the flash memory. Likely transitioning from RAM to the USB.

I don't have a great handle on all the data being written to the flash memory, but it includes all code updates (infrequent), Linux log (text data, low bandwidth), vehicle log (likely higher bandwidth), settings (trivial amount, infrequent), history such as navigation (infrequent), some images from the cameras - but perhaps only in a crash and other items less clear (could be frequent and large data). Other possibilities are more likely in RAM, but could flow through flash may include phone's contacts when the phone connects, streaming music, Google maps, navigation routing, and USB music/video buffering.

Darthamerica | February 8, 2020

It's logging and writing data anytime the car is powered up. Since the car's firmware is 3x to 4x bigger than it used to be. If any of the memory where the FW is written gets corrupted, you're done. It's just a matter of chance not mileage. And the chance is greater with each day. It's going to take a BOM and/or layout PCB change if the new part isn't pin compatible with the same footprint. It's a dedicated ~3 to 6+ to month effort to do it right.

jordanrichard | February 8, 2020

While I can see sentry mode logging a crap load of date, from the failures mentioned here on the forums, those cars are older cars like mine that don’t have Sentry mode or even AP1.

There are probably literally hundreds of posts about this, many by experts and wannabe experts, yet no one has stated what is the trigger point, time or miles? I have seen the articles by third party companies that will repair the MCU’s saying that the MCUs are only good for 4 year. If that were the case, then we would have been large amount of MCU failures starting in 2016.

tes-s | February 8, 2020

Car logs a lot - I think it used to log even more. Turn signal, brake, error messages, seat belt status.

When the service center "pulls the logs" I think that is what they are getting. They always ask for a time so they can find it in the log - which leads me to believe it is voluminous.

1LuckyGuy | February 8, 2020

asking again if anyone knows..Will Tesla install a privately purchased MCU? If not, can you just get one online and have it installed or does it have to be programmed?

Darthamerica | February 8, 2020

Jordan there is no “triggerpoint”. It’s just more more likely everyday until it almost inevitably happens.

jordanrichard | February 8, 2020

Well, the same could be said about a head gasket or fuel pump on an ICE. Both of which will leave you stranded and very expensive to repair, especially a head gasket.

Darthamerica | February 8, 2020

No, this is a lot different and many many times more likely and affects every car Tesla has made. The is a real design flaw and it needs to be fixed.