I had the 4Runner in the driveway, had been sitting there for 2 hours or so. All of a sudden the horn just started honking itself.

The keyfob would lock and unlock the doors, but not shut the horn. I disconnected the battery and reconnected and the horn stayed off. I started the truck no problem shut it off and the horn started again. I disconnected the battery and reconnected to shut the horn again.

I pushed the panic button on the FOB and the alarm went on, I shut the alarm and the horn stayed on.

I pulled the fuse to make sure it didn't turn on again.

Has anyone experienced this before? or can point me in the right direction to diagnose?

Thanks in advance.

I had an issue line this once. My panic button was being wedged in the plastic housing of the fob and not "releasing" if that makes any sense.

I was camping and it went off around 6 am and wouldn't stop. Took a while to figure out but hasn't been an issue since. Not sure if it's related but you might want to keep an eye on it.

Sent from my SM-T320 using Tapatalk

I am going to try and swap the horn and see what happens.

I wouldn't think it would be the horn it self. It has to have power to turn on. I'd smack the horn button pretty good a couple of times with your hand. If that doesn't do it you may have a short somewhere or the clock spring might be going bad.

Edit: added "button" to horn

Went through this a few years ago with my Gen 5. The problem was in the steering wheel which required replacing the airbag (expensive). Just pulled the fuse and survived without a horn for a few months. When I put the fuse back in the problem had resolved itself.

I tried hitting the horn button, with the car off. As soon as I turn the key to the on position the horn stops and works normally.
I pulled and checked the fuse, I am going to do the same with the relay.
I really hope it not in the steering wheel like HNTMUP had.

might be either the relay, but sounds like a bad clock spring cable.

I believe I narrowed it down. everything is working again.

Didnt see anything wrong with the relay.

The horn stops when the car is on so I have eliminated the horn button.

I did have a little bit of water running down my A pillar Friday night during very heavy rain. I am thinking the water caused a short in the relay or on the back of the relay box.

I am going to check the sunroof drain and look into having the windshield reset.

If it's working again I would pray to our Blessed Mother of Acceleration that she has smiled mercifully upon you and smote your gremlins.

If (when) it happens again I would swap the relay because it's cheap ($4-$10) and, it's rare, but they sometimes fail closed when contacts corrode, arc, and weld themselves together. They usually fail open though.

Unfortunately... I've got to agree with riceandpho. I think it's the clock spring (~$200). They have a tendency to short when they fail. I'm 95% sure you have a short on the low voltage side of the relay and 85% sure that the clock spring is the weakest link in that chain. (Take those numbers with a grain of salt.)

I doubt its the horn itself or the actual horn switch in the steering wheel. When they break they usually just don't work.

Anyone know how to fix this problem on a 99 T4R? My horn turns on and stays on when the ignition is turned to the on position. I've ruled out the clock spring by taking apart the steering wheel and testing that the wire is not grounded. The horn button works fine when the vehicle is off too.

Before this problem started, I pulled out the fuse box to check diagnose a problem with the wipers. That was resolved and I plugged everything back in. After that, I started the vehicle and the horn started sounding. It won't stop when the ignition is in the on position.

I'm thinking it has to do with the relay in the ECU or there's a wire crossed somewhere that's sending power to the horn. I don't have any alarm components on the vehicle, and this doesn't seem like the typical symptoms people are having with their alarms since the horn only comes on when the vehicle ignition is on.

BINGO! I had the exact same issue with water coming down the A-pillar due to a clogged sunroof drain line. The horn would go off randomly. It was an embarrassing frustration since I was at home confined to hospital bed at the time recovering from a motorcycle accident. My neighbor disconnected the horn thankfully. Once I was on my feet I addressed the water intrusion and the problem has not returned.