SERVICE BRAKESOn our drive back from Yosemite, we began descending from Groveland, CA after leaving the Rivian charging station. Due to heavy rain, the car ahead of me was moving cautiously, limiting my speed to about 20 mph while maintaining a safe distance during the descent to Moccasin, CA. Thanks to the regenerative braking, I didn’t need to apply the brakes, as the car automatically slowed when I wasn’t pressing the throttle. However, my windows started to fog up, so I turned on the defoggers. Shortly after, I noticed the car’s door locks repeatedly unlocking and locking by themselves. As we neared the bottom of the descent, I began to smell something burning from the vents. This prompted me to step on the brake pedal for the first time, but it felt unusually stiff, with little travel. The car didn’t slow down, and the burning smell intensified. I pressed the brake pedal repeatedly, but it felt stuck, and the car did not decelerate. Eventually, I was able to roll to a stop. I pulled over to a side street where the issue persisted. I turned off the defogger and contacted Rivian via SOS. We were able to replicate the brake issue on the side street: as I maneuvered the car, the brake pedal sank on its own when the defogger was on. Once I turned it off, the pedal returned to normal. There were no warning lights or alerts from the car system. When I got out of the car, the burning smell was strong near the front wheels. It was clear that my family’s safety was at risk, including 3 young children. The car was towed to a service center, where it’s being inspected. Rivian hasn’t been able to reproduce the issue yet. I believe the regenerative brakes weren’t working properly, causing the car to rely on the regular brakes for the entire descent. This likely led to brake failure at the bottom, with the burning smell originating from overheated brakes. I also suspect that the overheating caused other electrical issues, which could explain why the door locks kept cycling on and off.