2002 passat horn comes on by itself when key turned to on position and wont stop

Have you tried putting the key into the ignition switch and starting the car ?

In some vehicles, you can place key into driver door cylinder and manually lock / unlock which may turn horn off.

Sounds like you either need another lock cylinder for your ignition or your central electronics module needs to be readapted in the CPU. When you insert your key back in and turn to the start position does your car start? How about when you remove the key now? If it won't start now, or if the ignition lock cylinder doesn't move freely, then you probably need a lock cylinder. Adapting your central electronics involves finding someone with a VAG COM cable and laptop, with the information provided in the wiki at VAG COMs website. For instructions on replacing your ignition look in the forums on VWvortex.com

ignition switch keylock cylinder is broken.

Might be some obstruction in the lock cylinder itself.

try another key. the key could be worn where read coil in the ignition switch lock cylinder and immobilizer control module and ecm dont recognize ignition key or ignition switch key lock cylinder failing.

SECTION 211-04: Steering Column 2002 Escape Workshop Manual REMOVAL AND INSTALLATION Ignition Switch Lock Cylinder Removal and Installation
All vehicles

1. Disconnect the battery ground cable. For additional information, refer to Section 414-01 .

1. Turn the ignition keys to the ON position.

Early build vehicles

1. Remove the upper steering column shroud.

1. Remove the screws and the lower shroud.

1. Using a small tool, press the ignition lock cylinder release button and pull the ignition lock cylinder out.

Late build vehicles

1. Using a small tool, press the ignition lock cylinder release button in the hole and pull the ignition lock cylinder out. Usually, the key has to be in the oN position to do this step.

All vehicles

1. To install, reverse the removal procedure.

Step1 Disconnect the negative battery cable from the terminal on the battery. Remove the upper and lower steering column covers by unscrewing or unclipping them. Step2 Remove the steering wheel by lifting off the center cover, disconnecting the horn wire and removing the retaining nut and washer. Make a mark on the steering wheel spline and the wheel itself so you can line it back up precisely. Pull the steering wheel straight back to remove from the shaft. Step3 Take off windshield wiper and turn signal switches by pulling them off as you did the steering wheel and disconnect the wiring. Slide the spacer sleeve off of the steering column. Step4 Unscrew the ignition switch mounting screws. Pull out the ignition switch. Disconnect the wiring connector from back of the ignition switch. Simply loosen the tabs and pull it out. Step5 Insert your key into the ignition. Turn the ignition switch to the locked position. Depress the retaining pin with a small screwdriver and turn the key to the Off position to free the cylinder. Once it is free, turn the key to lock position and remove the key and key cylinder. Step6 Install your old key cylinder into the new ignition switch assembly. Make sure the contacts in the cylinder and assembly line up. Reattach wiring to ignition switch, slide it into place, screw in mounting screws and reassemble steering wheel and switches.

Try cleaning the key and ignition switch with alcohol or electric contact cleaner. Try a different key if you have one. And GM's are known to have problems with the ignition cylinder and theft deterant system. A new ignition cylinder costs $280-$300. Sometimes you can turn the key to the run position wait ten minutes and then start it. Some people say you have to turn the cylinder to the off but not lock position before starting after waiting the ten minutes, but my sister didn't have to with her Malibu.

if the ignition wont turn at all it is probably the ignition cylinder itself, try wiggleing the steering wheel while turning the key, if this doesnt help you will need to replace the lock cylinder

it sounds like the ignition cylinder has worn, when you try to stick anything into the ignition besides the key it respond by freezing the system. due to the cylinder being worn the key does not fit correctly, then the ignition picks up on this and tells the car it's being stolen.replace the ignition cylinder(lock and tumbler) and it should be fine. this usually happens when the keys are too heavy and causes the key to pull downward and dent the cylinder