Possible wrong rotors???
Possible that the rear sensors are broken.
Front Brake Rotors can be a pain, I would recommend going to your local Pepboys, Kragen, O' Reilly's or AutoZone Near you. They will need your year and model of vehicle.
You either have a bad brake caliper or the brake hose is bad.
A frozen brake caliper or if you just instaled new brakes and rotors you might have oil on the rotors as they need to be clean before installing.
I just paid $500.00 to replace all brake pads and the front rotors
You probably have a warped brake rotor. New rotors are fairly inexpensive, I would replace both front rotors and brake pads while your in there. The calipers and sliders along with the brake hoses and lines need to be examined also.
You probably have severely warped front brake rotors. Machining or replacement of the rotors would be necessary to correct the problem
The most likely problem is warped rotors. Have rotors turned or replaced. Replace front brake pads.
Because the front rotors are warped. You might want to replace the rotors or resurface it.
Your front brake rotors are warped. They need to be removed and turned true on a lathe. Many auto parts stores offer this service.
Normally,when replacing front pads, the rotors and calipers should be inspected for replacement as well. When you step on the brake, this activates the calipers to press the brake pads against the rotors. The symptoms you are describing more than likely mean the rotors need to be replaced as well, possibly they are warped. However, 3 parts are involved that work in unison, so examine all three, both sides. Some Sienna's have a four wheel disc brake option..examine all four. Good luck.
The front rotors are out of round are warped. Turn are replace rotors and be sure to replace the brake pads even if thay look good. I would also check the tie rods too.