One problem related to brake master cylinder has been reported for the 2006 Toyota Sienna. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2006 Toyota Sienna based on all problems reported for the 2006 Sienna.
I was driving approximate 25-30 mph on a dry, level street. A car stopped in front of me to make a left hand turn. I applied the brakes and nothing happened. I released and reapplied the brakes again and again no response. I was able to swerve to the right into an empty parking lot to avoid hitting the car or another collision. After swerving and reapplying the brakes a 3rd or 4th time I was able to come to a stop. My kids and I were severely shaken, but not injured. We decided this problem was due to the master cylinder. We replaced it and have had 3 more incidents since replacing the master cylinder. 1 was in reverse leaving my drive way. I wound up hitting and embankment across the street to stop me. This was a slight down hill roll in reverse. I went from parked to out of control. I never touched the accelerator and hit the brake multiple times and even tried shifting back into park (knowing that's bad for the transmission), nothing worked. After getting stopped and pulling forward everything seemed normal again. My husband was driving in traffic and we were approaching a turn and had to merge in to perpendicular traffic. Approx speed 25-35 mph. The brakes again completely failed and we had to swerve through a traffic light in to a free lane of traffic to avoid a rear end collision with the cars infront of us. We ordered another master cylinder and were preparing to install it. Today the brakes failed again at a stop sign (approx speed 5-10 mph) I had been stopped and started to ease in to the main road when I saw a car coming from the left.