Horn on my sienna goes off while replacing the battery

Hi,

When you start the vehicle try to step on the brake pedal then try to shift it to drive or park.

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First use a battery charger to charge the battery, instead of a jump start. Second, with a complete dead battery you may want to pull the connection for the horn under the hood till the battery is completely charged.

sounds like the anti-theft system is activated

check all connections for tightness, sounds like one is loose somewhere between the battery and the starter or a ground is not tight..turn lights on and see if they go dead when key start is turned,,check the engine to frame ground also(usually a flat braided wire)..if lights go dead when key is turned need to charge the battery for around 4 hrs with a 6 amp charger and try again..may also be a neutral safety switch,,if not out of gear it wont start,,

Clean the battery cables, you must have a bad connection, use baking soda in a hot water solution and soak the cable ends and then wire brush and clean the opening with a battery cable cleaning tool available from any parts store for about $2.00

Check the battery, try to jump start with another car, it sounds like the battery is dead.

This is caused by a part called the clock-spring rotating contact ribbon, it is a coiled up circuit ribbon that connects the steering wheel button and airbag to the steering column electrics. it is under the steering wheel. It needs to be replaced. This can be a dangerous job due the Airbag, so if you do want to try and replace it disconnect the battery negative cable for 15 minutes prior to start of work. The part is about $150.00 You will need special tools.

some will reset by locking and unlocking the door with the key.....or .need to replace the battery in the car it is dead and when u try to reset it trips again because it is dead

short in wiring/switch probably set off horn, which then killed your battery. Disconnect horn to replace battery, then troubleshoot horn switch.

The horn relay is stuck. The fuse box is right by the battery, remove the horn relay (it pulls straight out) and replace. The guide is in the lid. Removing the relay (or the 10A fuse, tool is also in the box) will stop the horn, but the relay's contacts are probably locked.

Sometimes just a little shock will dislodge the contacts that are locked together, but it's probably worth replacing with new.