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The MCU for my 2018 P3D needs to be replaced. How common is this?

joebruin77

Active Member
Dec 23, 2018
1,127
985
Encino, CA
Earlier this week, my family and I returned from a road trip with my 2018 P3D (which has about 22K miles on it). The car was great - no issues, no error codes, no signs of any problems. At 10pm the night after we got home, I tried to start charging the car through the Tesla app but the app could not connect to the car. I thought perhaps the server was down or perhaps the car needed a reboot. I woke up the next morning to go reboot the car and the car would not turn on. The screen was completely dark. I tried a reboot by placing my foot on the brake pedal and holding down the scroll wheels, but nothing would happen.

I called Tesla roadside assistance and they sent out a tow truck. The driver and I both thought that the 12volt battery was the culprit. He gave the 12volt battery a jump and although the screen was still dark, after the jump, I could put the car in drive. With the screen still completely out, I managed to drive my P3D to my local service center. I have to say the service center staff were awesome. They were super helpful even though I did not have an appointment. They took the car and gave me Uber credits to get home. I thought they would call me later to tell me that my 12 volt battery was replaced and I could come pick up the car.

I was surprised to get a call from the service center rep that they diagnosed the problem as a faulty MCU and that the MCU had to be replaced. They did not have this MCU in stock and had to order the part. They arranged for me to have a rental car through my local Enterprise on their dime.

The purpose of this post is not to complain about Tesla service. In fact, I was quite impressed with how prompt and smooth their service was. The tow truck arrived in a timely fashion, the SC rep gave me timely updates and had great communication with me, they took in my car even though I did not have an appointment, and they gave me a rental car on a Friday afternoon. I already got two email updates on the status of the MCU part that has been ordered.

My concern has to do with the fact that the MCU needs to be replaced in a car that is only 2.5 years old and only has 22K miles. How often does this happen? Has anyone else had this problem? Are MCU's made today more reliable than the original MCU from my 2018 car? How likely am I going to have to replace the MCU in another 22K miles?

I welcome your comments and answers.

Thank you,
joebruin77
 
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glide

Active Member
Jun 6, 2018
3,662
3,827
USA
Earlier this week, my family and I returned from a road trip with my 2018 P3D (which has about 22K miles on it). The car was great - no issues, no error codes, no signs of any problems. At 10pm the night after we got home, I tried to start charging the car through the Tesla app but the app could not connect to the car. I thought perhaps the server was down or perhaps the car needed a reboot. I woke up the next morning to go reboot the car and the car would not turn on. The screen was completely dark. I tried a reboot by placing my foot on the brake pedal and holding down the scroll wheels, but nothing would happen.

I called Tesla roadside assistance and they sent out a tow truck. The driver and I both thought that the 12volt battery was the culprit. He gave the 12volt battery a jump and although the screen was still dark, after the jump, I could put the car in drive. With the screen still completely out, I managed to drive my P3D to my local service center. I have to say the service center staff were awesome. They were super helpful even though I did not have an appointment. They took the car and gave me Uber credits to get home. I thought they would call me later to tell me that my 12 volt battery was replaced and I could come pick up the car.

I was surprised to get a call from the service center rep that they diagnosed the problem as a faulty MCU and that the MCU had to be replaced. They did not have this MCU in stock and had to order the part. They arranged for me to have a rental car through my local Enterprise on their dime.

The purpose of this post is not to complain about Tesla service. In fact, I was quite impressed with how prompt and smooth their service was. The tow truck arrived in a timely fashion, the SC rep gave me timely updates and had great communication with me, they took in my car even though I did not have an appointment, and they gave me a rental car on a Friday afternoon. I already got two email updates on the status of the MCU part that has been ordered.

My concern has to do with the fact that the MCU needs to be replaced in a car that is only 2.5 years old and only has 22K miles. How often does this happen? Has anyone else had this problem? Are MCU's made today more reliable than the original MCU from my 2018 car? How likely am I going to have to replace the MCU in another 22K miles?

I welcome your comments and answers.

Thank you,
joebruin77
No one knows how often it happens. Tesla doesn’t release that data and the M3 is a fairly new vehicle.

MCU failures in the older Model S were fairly widespread but the root cause of that issue was different.

There have been no material changes since the 2018 model year to my knowledge.
 
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jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
10,293
11,631
Riverside Co. CA
Earlier this week, my family and I returned from a road trip with my 2018 P3D (which has about 22K miles on it). The car was great - no issues, no error codes, no signs of any problems. At 10pm the night after we got home, I tried to start charging the car through the Tesla app but the app could not connect to the car. I thought perhaps the server was down or perhaps the car needed a reboot. I woke up the next morning to go reboot the car and the car would not turn on. The screen was completely dark. I tried a reboot by placing my foot on the brake pedal and holding down the scroll wheels, but nothing would happen.

I called Tesla roadside assistance and they sent out a tow truck. The driver and I both thought that the 12volt battery was the culprit. He gave the 12volt battery a jump and although the screen was still dark, after the jump, I could put the car in drive. With the screen still completely out, I managed to drive my P3D to my local service center. I have to say the service center staff were awesome. They were super helpful even though I did not have an appointment. They took the car and gave me Uber credits to get home. I thought they would call me later to tell me that my 12 volt battery was replaced and I could come pick up the car.

I was surprised to get a call from the service center rep that they diagnosed the problem as a faulty MCU and that the MCU had to be replaced. They did not have this MCU in stock and had to order the part. They arranged for me to have a rental car through my local Enterprise on their dime.

The purpose of this post is not to complain about Tesla service. In fact, I was quite impressed with how prompt and smooth their service was. The tow truck arrived in a timely fashion, the SC rep gave me timely updates and had great communication with me, they took in my car even though I did not have an appointment, and they gave me a rental car on a Friday afternoon. I already got two email updates on the status of the MCU part that has been ordered.

My concern has to do with the fact that the MCU needs to be replaced in a car that is only 2.5 years old and only has 22K miles. How often does this happen? Has anyone else had this problem? Are MCU's made today more reliable than the original MCU from my 2018 car? How likely am I going to have to replace the MCU in another 22K miles?

I welcome your comments and answers.

Thank you,
joebruin77

I also read the model 3 forums fairly extensively (as would be expected from a moderator, I guess), and dont remember seeing another instance of this particular problem.

With that being said, do you have FSD? I also have a 2018 model 3 performance (so same vehicle), but I have FSD so had the 2.5 computer replaced with HW3.0 when that was available for me.

I believe that the MCU is on that same computer board, so in effect, getting the HW3 upgrade also replaces the MCU. I am curious if you have FSD and this is a failure of the MCU on a HW3.0 computer, or if its HW2.5. These cars are not "that" old, relatively speaking so it would not be super unexpected that some of the older ones show "something".
 

fajitamondays

Supporting Member
Supporting Member
Mar 5, 2019
241
344
WA
Mine fried itself with less than 200 miles on the odo. It was a real joy having the screen go dark while on freeway with Autopilot on. 12/31/2018 build (LR AWD).
 

joebruin77

Active Member
Dec 23, 2018
1,127
985
Encino, CA
I also read the model 3 forums fairly extensively (as would be expected from a moderator, I guess), and dont remember seeing another instance of this particular problem.

With that being said, do you have FSD? I also have a 2018 model 3 performance (so same vehicle), but I have FSD so had the 2.5 computer replaced with HW3.0 when that was available for me.

I believe that the MCU is on that same computer board, so in effect, getting the HW3 upgrade also replaces the MCU. I am curious if you have FSD and this is a failure of the MCU on a HW3.0 computer, or if its HW2.5. These cars are not "that" old, relatively speaking so it would not be super unexpected that some of the older ones show "something".


I do not have FSD. At the time of purchase, I did get Enhanced Autopilot, but no FSD. I believe this is the 2.5 version and they are replacing it with another 2.5 version. Glad to hear this is not a common problem. Hopefully it will get replaced soon. Tesla was kind to arrange for my rental car, but man it is hard to go back to driving an ICE car. I have to start keeping track of gas prices again....Ugh!
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
10,293
11,631
Riverside Co. CA
I do not have FSD. At the time of purchase, I did get Enhanced Autopilot, but no FSD. I believe this is the 2.5 version and they are replacing it with another 2.5 version. Glad to hear this is not a common problem. Hopefully it will get replaced soon. Tesla was kind to arrange for my rental car, but man it is hard to go back to driving an ICE car. I have to start keeping track of gas prices again....Ugh!

Yeah, our 2018 Model 3s came with HW 2.5. I (like you) bought enhanced autopilot on purchase as the car was already 71.5k (pre tax credits etc) with that, and FSD was another 3k on top of that. The only reason I have FSD is I bought it during the 2k fire sale in 2019, as I felt like 2k was a decent price for the new hardware + installation, even if FSD never added a single new feature over EAP.

In any case, I hope this is not indicative of a more widespread problem. Thanks for sharing.
 
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Perscitus

Member
Jan 29, 2019
891
571
New York
Too bad Tesla will not release any historical data on this that might allow for some correlations to be made between these failures, or connectivity board or any daughter card failures and AP2.5, 3.0, 3.1 and current 3.5. that they are installing across the 3/Y fleet.
 
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joebruin77

Active Member
Dec 23, 2018
1,127
985
Encino, CA
I am happy to hear this is a rare problem, at least based on a lack of reports on TMC forums.

Could the MCU failure be heat related? I do park my car outside 24/7 and I live in a part of California with very hot summers. I am wondering if excessive heat may have fried the MCU. Or is the MCU engineered to handle such hot temperatures?
 

Frank99

April 2018 Model 3 LR RWD, EAP, FSD
Apr 7, 2016
309
408
Arizona
I got my Model 3 in May 2018, and for the first summer here in Phoenix the Cabin Overheat Protection feature didn’t exist, so every time I parked in the sun, the interior got the full effect of bright sun and 110F temperatures. No issues.
Tesla, like other auto makers, uses electronics designed and spec’ed to take that heat.
 
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fajitamondays

Supporting Member
Supporting Member
Mar 5, 2019
241
344
WA
Sorry to hear that. How long did it take Tesla to replace it? And have you had any problems since it was fixed?
They had it ready for me right before closing the next day. I was in touch with the service manager ahead of time (while Tesla Engineering was remote diagnosing the issue), and they were able to line up a replacement MCU ready to swap in when I brought the car in. The MCU deteriorated to the point where it was crashing several times even on really short drives.

I've had no related issues after the replacement (22k+ miles ago), and have since gotten the HW3 upgrade, which may have been another MCU replacement as I think the AP computer and MCU are one unit on the Model 3.

I've had my car in for numerous other issues (I chalk it up to the 12/31 build date), but this was the one time they couldn't offer me a Tesla loaner, so they shuttled me to the local Enterprise for an ICE loaner. Infiniti QX30, which usually would be a considered a nice rental, but absolutely zero joy in driving that around, and I nearly rear-ended a car at the first light! Forgot about the whole no regen braking thing :p
 

The_Observer

Member
Feb 14, 2020
730
454
Los Angeles
Too bad Tesla will not release any historical data on this that might allow for some correlations to be made between these failures, or connectivity board or any daughter card failures and AP2.5, 3.0, 3.1 and current 3.5. that they are installing across the 3/Y fleet.

What's AP 3.1 and 3.5? 3.5 referring to no radar? What's 3.1?
 

Perscitus

Member
Jan 29, 2019
891
571
New York
AP hardware revisions ...


Just like there is MCU1 and MCU2:
 

lolder

Member
Jun 11, 2016
906
697
SW Florida
Yesterday my 28,000 mile 2018 M3 RWD did not wake up the screen when I got in it. Open and closing door seat belt, etc. did not turn it on. It did go into reverse and drive. I did a double button reset and it came on. Today it was normal. I think this is a software bug, not a MCU problem.
 

joebruin77

Active Member
Dec 23, 2018
1,127
985
Encino, CA
Yesterday my 28,000 mile 2018 M3 RWD did not wake up the screen when I got in it. Open and closing door seat belt, etc. did not turn it on. It did go into reverse and drive. I did a double button reset and it came on. I think this is a software bug, not a MCU problem.
Glad to hear the reset worked for you. In my case, I tried the reset several times to no avail.
 

joebruin77

Active Member
Dec 23, 2018
1,127
985
Encino, CA
Just a quick update, the MCU was successfully replaced by my local Tesla SC. I am happy to report the quality of the service I received was outstanding! They replaced the MCU within 2 business days and gave me a rental car to use while the part was being shipped and the service was being completed. The service rep was in frequent contact with me. I believe Tesla has improved the quality of their service and I wanted to share the good news.

In terms of why my MCU failed and had to be replaced after only 2.5 years, I was curious about the following two possible factors:

1) I never used cabin overheat protection before. My car is parked outside and can often reach internal temps of 140-160 degrees. Could this have contributed to an early death for my MCU? Should I go ahead and use the cabin overheat protection to reduce the risk of any damage to my new MCU?

2) Early on, I applied one of those glass screen protectors to prevent the glass from being scratched. Is it possible that this extra layer of glass could act like a piece of insulation, trap heat inside the MCU, and contribute to an early demise? If so, I will forgo a new screen protector.

I welcome any thoughts so I know how to better protect my new MCU.

Thank you,
joebruin77
 
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