2015 Sienna awd w/83k miles. Never any problems until yesterday. Normally as long as smart key is within a couple feet of pushbutton starter button van fires right up. Now it is dead unless you hold the smartkey on the pushbutton - the method you use when keyfob battery fails. Before replacing fob battery it worked locks and lights and sliding doors but did not interface with starter button to start engine.

Replaced batteries in both fobs to no avail. When fob is held on starter button, car battery cranks strong and starts fast. Several on Sienna Chat forum have had same problem with no defined remedies.

Any one else ever deal with this?

Just a wild guess but take that new watch battery and clean BOTH sides with alcohol.
I replaced mine last month and had read that they now come with a rancid taste film in case a child puts it in mouth.
See if that works.

Do you have any of the no key fob detected warning or replace your fob battery warning before and/or during having this issue? Is this happen with all the fobs? Also whe you test that only one fob is within the vicinity of the van.

SeaCliff is right. The bitter coating to keep kids from eating batteries does not play nice with lots of electronics. You can buy ones without it, the package will usually have a kid with the red X through it or you should be able to clean the ones you have.

thanks for the replies but both remote batteries are good and I have tried them separately. The remotes each work the lights, door locks, sliding doors - they would not do that if the batteries were bad and the smart key itself has a red led visible when the case is open that lights up to verify the battery is good. CR2032.

My guess is something wrong with the ignition pushbutton - either faulty or somehow lost programming?

Stop by the Parts dept at the dealership they will know.