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Brake booster failure on brand new Model Y

Less than 2 weeks after picking up our brand new 2021 Model Y LR, we experienced a scary partial brake failure in the middle of driving. Symptom was the brake pedal becoming very stiff; it took great leg strength to press down the pedal to have some braking effect. The orange brake warning light was on, as well as two alerts: IBST_a082 "Power braking assist reduced" and DI_a245 "Vehicle Hold feature unavailable".
Screenshot 2021-04-15 224642.png

We pulled over and looked up what these errors mean. According to the owner's manual it seems the "brake booster" has failed, but the backup hydraulic boost compensator can still function, providing some amount of brake assist. Fortuantely we were on a local road not far from home, and regen braking was working fine, so we decided to cautiously drive home (and we made it to home safely). But what a strange and scary experience! Who would've expect a brand new car to have brake failures? What if this happened when we were driving 70+mph on a highway and needed to emergency brake??

Both errors went away after leaving the car for a while (effectively power cycled). But I am unwilling to believe it was a software glitch. If it happened once, it could happen again (perhaps even on the highway). I scheduled an appointment with my nearest SC for next week. Got a message within the same day saying I could brought the car in any time during business hours since this is a safety issue. The service advisor also said I could have the car towed to SC if I felt unsafe driving it. Brought the car in the morning after (days ahead of my appointment slot), SC immediately took the car in and started diagnostics. Around noon I got a call from the service advisor saying they looked the logs and it is very likely the brake booster is faulty, so they are going to replace the entire brake booster assembly:

Service provided by the Fremont SC has been really great. At least they are willing to replace the faulty part instead of telling me to just "power cycle the car and it'll be ok". But c'mon Tesla. I can tolerate cosmetic defects like misaligned panels and gaps. But defects in a safety-critical component in a brand new car?? That's too much. They really need to step up their quality control, be it IQC or OQC.

Also, I recommend all Model Y owners to closely study the "Braking Systems" section in the owners manual (page 60). Make sure you are prepared to exert enough leg force to brake in case the brake booster fails. Also know that you could press and hold the P button on the drive stalk to engage emergency braking in dire situation. Only use this if absolutely necessary.

Hope this doesn't happen to anyone else.

Another thing I noticed -- it seems the IBST_a082 and DI_a245 alerts tend to be preceded by the DI_a173 "Both pedals pressed" alert. See this other post: Power braking assist reduced

I drive with one foot and I don't have a big foot/shoe, so I am pretty sure I didn't press both pedals at once. The "both pedals pressed" warning could be a side symptom of a faulty iBoost. Or alternatively, say I did somehow press both pedals at the same time, but if that caused the iBoost to fail, then something is very wrong with the brake design.

Anyway, just a wild guess that there might be some correlation.
Happened to my C6 Z06 corvette with 400 miles. I thought that the vacuum line just popped off, but it turned out to a bad brake booster.

The hydraulic braking system in Teslas are fundamentally the same as all cars. The difference is there’s a pump instead of vacuum assist from the engine. In both vehicles, the driver will have to press the pedal very hard to stop when the hydraulic assist systems fail (brake booster). The pedal is still directly tied to the brakes mechanically/hydraulically.

It happens, and glad you made it home safely.
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Got car back yesterday (4th business day after drop off). SC has replaced the iBooster and did a road test to ensure functional brakes. Kudos again to the Fremont SC for addressing this issue so quickly.

I also tested it myself by purposefully pressing both the brake and "go" pedals. Got the "both pedals pressed" warning as expected, but no brakee failures. Drove home; all seems to be good now.

Fingers crossed this doesn't happen again.. but still, I should do more squat exercises just in case I need that life-saving leg strength 😅
Honestly, we are still planning to purchase a M3 later this year (our first Tesla) and the news of this issue had us a little concerned (at first). But, now it seems that it's an issue that has plagued vehicles for quite some time (experienced this in my past car/truck ownership when the vacuum assist fails for this or that reason). It's nice that the Tesla actually warns you of the issue (My old 1970's F-150 didn't!)

I'm glad you made it home safe and that it's something that's fix-able!
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