Horn stuck on/P lock malfunction help request

I wonder if @SFO or @ChapmanF could help?

Basically, you need to test the horn circuit to isolate the problem. First step would be giving electrical power to the horn in the amount it needs to confirm the horn isn't the source of the malfunction and then you'd work your way back up the circuit.

Also I can say from personal experience in my teenage years I have several memories of friends who had their horns stuck on and couldn't get it turned off and kept driving around like that for days, sometimes weeks... Lol... Cars in the 1980's still had problems like that.

Also on a more serious note my sister's volkswagon rabbit I used as my first car had a broken horn that I ignored getting fixed until one day a lost UPS driver backed up a steep hill with me behind him and he couldn't see me and I kept yelling and he didnt here me. Finally, when he stopped I jumped out of my car to get his attention and he started backing up again and I had to jump in the car and back up again. Finally he heard me burning rubber trying to back up fast enough.

Seriously folks, don't drive a vehicle that doesn't have a functional horn! It's not worth the risk!

 

Check for codes with a Prius aware scanner, corrosion is often a culprit

 

Pulling that fuse killed abs mtr 1, abs mtr 2, and everything fed by the integration relay (including the horn, low-beam headlights, backup lights, defoggers, PTC heaters, and the system that shifts the transmission in and out of park).

 

I hate when that happens

 

I was just getting ready to say You got the wrong fuse out there's one clearly marked horn I do believe but I think it might be inside the car or you could just literally unplug the horn under the hood seriously and not touch any fuses just unplug the horn then while you're testing the horn you could put a light bulb to ground from the horn contact now the light bulbs lit and you can see that while you're working on the mess and when it goes out while you're inside the car you found your problem on a Gen 3 You may have to undo the clips on the horn pad and lift that up and see does it feel like you're horn button still pushes in and out I have a Gen 3 steering wheel in the generation 2 car that's the only thing I don't like about the steering wheel is the horn button and the way it clips on instead of the normal torx bit or whatever screws

 

No separate horn fuse in gen 3. The high-pitch (blue) and low-pitch (black) horn wires just run straight from the integration relay to the horns. The overcurrent protection for them is in the integration relay itself.

The horn switch arives at the integration relay as a sky-blue wire at 1G pin 18. It should normally be open-circuit, and is pulled to ground when the horn pad is pushed.

If the integration relay puts 12 volts on pins 5 (blue) and 6 (black) when 18 (sky blue) is grounded, and not when 18 isn't grounded, then the relay is doing what it's supposed to.

If pin 18 is being pulled to ground when no one is pressing the horn pad, something is funky in the switch wiring or spiral cable. Conversely, if it's not being pulled to ground then but the integration relay is still supplying power on 5 and 6, then the relay is kaput.

 

You should be back to normal operation although the horn is shorted the ground and beeping constantly but the horn is unplugged so that load is gone now your car should be back to the way it was before whatever happened to the integration relay foreign circuit I would think so when you move the car with the horns unplugged and integration relay set back in place and all that and he lights on to make you think that something's wrong and then there's probably not I would be driving mine to see if it would and it should.

 

Now who can argue with that?