under the dash
Get a Toyota shop manual before you attack the dash. There are a number of screws and clips that are not obvious, and there is a good chance you will get frustrated and break something if you just go at it. On the Sienna, I had to remove a good portion of the dash just to change light bulbs on the instrument cluster. I have a shop manual, and the job went smoothly. But I would have not figured it out without the instructions.
The 2001 Toyota Sienna OBD 2 port is on lower edge of dash; mounted on a bracket above accelerator pedal
I cannot find how to remove the cup holder from the dash of my 2001 Pontiac Montana
The 2006 Toyota Sienna OBD 2 port is on "lower edge of dash, left of steering column"
Under the dash near the driver's right knee.
The 2002 Toyota Sienna OBD 2 port is on lower edge of dash; mounted on a bracket above accelerator pedal
I have a 2000 sienna..........and had that light come on......in has to do with the braking system
Carefully
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Look under the dash behind the coin holder. Cheers
on my 98 sienna there is a button on the left side of the dash lower part with a push button not sure if it is in the same place on all models hope that helps