Shudder when autopilot brakes

[RCH1708]

Hi, I have an MX from Sept 2018 and it has had this problem since new. It's related to the TACC and can be induced - if you're brave enough - by sitting behind a truck with the TACC engaged, then briefly accelerating hard towards the truck, overriding the TACC, then taking your foot off the accelerator. This forces the TACC to brake hard (to avoid running up the back of the truck!) and usually results in a horrible noise from the front end. It sounds like sprung pressure relief valve oscillating or something. It's definitely hardware and not something that can be fixed with a firmware upgrade.

I've asked the Service Centre about it multiple times, but every time I'm told that its normal. Personally I don't believe a word of it - I suspect that it is a "cosmetic" problem with a poor quality component and that is too expensive for Tesla to replace. Eg similar to the 'yellow edge' problem of the central display screen.

If anyone has managed to get this problem solved, I'd be interested to know. I hate it.

 

[mxnym]

Hi, I have an MX from Sept 2018 and it has had this problem since new. It's related to the TACC and can be induced - if you're brave enough - by sitting behind a truck with the TACC engaged, then briefly accelerating hard towards the truck, overriding the TACC, then taking your foot off the accelerator. This forces the TACC to brake hard (to avoid running up the back of the truck!) and usually results in a horrible noise from the front end. It sounds like sprung pressure relief valve oscillating or something. It's definitely hardware and not something that can be fixed with a firmware upgrade.

I've asked the Service Centre about it multiple times, but every time I'm told that its normal. Personally I don't believe a word of it - I suspect that it is a "cosmetic" problem with a poor quality component and that is too expensive for Tesla to replace. Eg similar to the 'yellow edge' problem of the central display screen.

If anyone has managed to get this problem solved, I'd be interested to know. I hate it.

As I believe I've stated to someone else earlier in this thread, what you are describing sounds like ABS and how it has worked on all cars for decades (since it was first introduced). Have you tried slamming on the brakes yourself from a similarly high speed to slow at a similarly dramatic rate? If you successfully trigger ABS, you will feel the brake pedal pulsing, and I suspect you'll hear the same sound. If you don't hear the same sound, perhaps the sound is just the brake pedal bouncing on a hydraulic piston that TACC actuates to brake. This second possibility is a guess, though, based on sounds I've always heard, because I don't know for a fact how it works mechanically.

 

[Kiomon]

I have this on my 12/2019 Build Raven Model X. My Model 3 didnt make this sound, so I think it's some type of mechanical play in the autopilot system and braking mechanism. OP did you ever get it resolved? My car is at SC now for delivery issues, and I had this on the list and they couldnt replicate it.

 

[jimbo_hippo]

Searched this topic to death. There are multiple threads but alas, no definitive solition outside of ‘it’s normal’.

Had a Model 3 for 17k miles/18 months and never heard it. Added a 2017 Model S to ‘the fleet’ 2 weeks ago and I’ve had this happen a few times. I’ve done some investigating of when the car does this and RCH1708’s description above is spot on. If you nudge the car faster overriding the TACC it happens when you release the throttle and the brakes kick in hard. Can’t make it do it under normal braking no matter how hard I try. it sounds to be coming from the right front to me but haven’t been a passenger yet so can’t confirm that. Be aware I’m RHD in the UK so I sit on the right.

Its a grating mechanical noise. it’s an alarming and unnatural sound for a car to make unless it’s broken so the idea of it being the norm is odd to me. The only consolation is I’m not alone in discovering it.