Horn malfunction

[Ken Timbers]

I hate having to admit my lack of technical skills, but I have a problem that has defeated what few of those I have. The car horn has started to have a life of its own, suddenly blaring away when there's no one nearby to have set it off—not even an animal. Worse still, it has now started to blare when I'm driving, for no discernible reason. It toots away for anything from a couple of times to half a dozen, which is embarrassing to say the least, and there's nothing I can do to stop it.

I thought it should be simple enough to find the relevant fuse and pull it out, going without a horn until I can get a mechanic at Lexus to look at it, but there isn't a fuse box where the manual says it should be and there's nothing else under the bonnet that looks like one. It talks about 'kick plates' that might perhaps conceal fuses, but I can't see a kick plate in either footwell—certainly nothing that's easily removable. Lexus (Sidcup) can't help today, suggesting I take the car in and leave it with them until they can find time to look at it next week—not really very helpful.

I can't leave the car like this on my drive, so I'm wondering whether I could simply cut the wires to the horns and have them reconnected when Lexus can take the car in. Does anyone have any suggestions?

[Herbie]

The usual places for fuse boxes are the engine bay and either or both of the front footwells, which can be seen by lying on your back with your head looking up towards the dash.

Is it under warranty at Lexus? If not, go to a proper auto-electrician, who will have it sorted in no time for you.

[Bob King]

1 hour ago, Ken Timbers said:

I hate having to admit my lack of technical skills, but I have a problem that has defeated what few of those I have. The car horn has started to have a life of its own, suddenly blaring away when there's no one nearby to have set it off—not even an animal. Worse still, it has now started to blare when I'm driving, for no discernible reason. It toots away for anything from a couple of times to half a dozen, which is embarrassing to say the least, and there's nothing I can do to stop it.

I thought it should be simple enough to find the relevant fuse and pull it out, going without a horn until I can get a mechanic at Lexus to look at it, but there isn't a fuse box where the manual says it should be and there's nothing else under the bonnet that looks like one. It talks about 'kick plates' that might perhaps conceal fuses, but I can't see a kick plate in either footwell—certainly nothing that's easily removable. Lexus (Sidcup) can't help today, suggesting I take the car in and leave it with them until they can find time to look at it next week—not really very helpful.

I can't leave the car like this on my drive, so I'm wondering whether I could simply cut the wires to the horns and have them reconnected when Lexus can take the car in. Does anyone have any suggestions?

The wires just pull off the horn connections , horns are mounted in east reach behind the front  grill.

[Malc]

I would tentatively suggest parking her on the Lexus Main Dealer forecourt ....... after close of business today of course .........  methinks they would pronto sort the problem for you Monday morning ..  and probably for free maybe 

Malc

[Lexiguy]

Hey Malc

I bet Ken 🙉 has already whipped the grille off, disconnected the wires, refitted the grill and tested it all within 10 mins of Bob 🦸 suggesting it! 

Ant

[Ken Timbers]

9 hours ago, Herbie said:

Is it under warranty at Lexus? If not, go to a proper auto-electrician, who will have it sorted in no time for you.

5 hours ago, Malc said:

I would tentatively suggest parking her on the Lexus Main Dealer forecourt ....... after close of business today of course

Hi Malc, I'd have been very tempted, but it would have been a hassle for me, too, and I decided to take an alternative, albeit expensive route. I took Herbie's advice and called out an auto electrician. I wanted peace of mind, not only for myself but for my neighbours, too—no chance of multiple alarms during the night and the ability to drive the car over the next few days without the irritation of a random beeping to annoy other motorists.

I shall certainly be putting the car into Lexus (Sidcup) for a proper examination and solution of the problem, but done at an appointed time, not just when they happen to have a spare moment!

[Bob King]

13 minutes ago, Lexiguy said:

Hey Malc

I bet Herbs 🙉 has already whipped the grille off, disconnected the wires, refitted the grill and tested it all within 10 mins of Bob 🦸 suggesting it! 

Ant

Good news 👍🏻
Two possible causes spring to mind…if the horn has its own relay in the fuse box under the bonnet, it could be sticking or have moisture in it …or underside of fuse box corroded .

Then the spiral cable behind the steering wheel is also an outside chance but that tends to stop the horn wiring altogether.

[Ken Timbers]

2 minutes ago, Bob King said:

Two possible causes spring to mind…if the horn has its own relay in the fuse box under the bonnet, it could be sticking or have moisture in it …or underside of fuse box corroded .

Then the spiral cable behind the steering wheel is also an outside chance but that tends to stop the horn wiring altogether.

The auto electrician was on  the ball, looked up the service manual on line to find the fuse number (which doesn't appear in the drivers' manual), recognised the fuse box under the bonnet (which I had failed to find!), and whipped out the relevant fuse. There was no sign of any malfunction, so I simply put it away in the console box ready to be replaced in due course. He tested the horn (not now working) and the lights and other functions seem to be well—all responded normally. Given that he had made the effort to attend at 8.30 pm on a Saturday, I was impressed by his performance—nice chap, too!

[ColinBarber]

32 minutes ago, Bob King said:

Two possible causes spring to mind…if the horn has its own relay in the fuse box under the bonnet, it could be sticking or have moisture in it …or underside of fuse box corroded .

Then the spiral cable behind the steering wheel is also an outside chance but that tends to stop the horn wiring altogether.

The body ECU can also sound the horn through the relay - used when the security alarm is set off. But this is very unlikely to be the issue.

Relay/horn button/clock spring all need to be checked.

[Ken Timbers]

I’ll pass on the combined comments to the Lexus service department when I take the car in. They may have a technician who has some experience of this model, but it could help a less knowledgeable chap to source the problem. 
Meanwhile, does anyone know where to find a key to the fuse layout? There isn’t one in the driver’s handbook or the fuse box, so I won’t be any the wiser if I have another problem involving fuses!

[ColinBarber]

2 minutes ago, Ken Timbers said:

There isn’t one in the driver’s handbook or the fuse box, so I won’t be any the wiser if I have another problem involving fuses!

They normally have the fuse layout on the underside of the fusebox lid.

[Ken Timbers]

 

2 hours ago, ColinBarber said:

They normally have the fuse layout on the underside of the fusebox lid.

The auto electrician did look at the inside of the fusebox lid and then went to his computer to look for information from elsewhere (service manual, I think). Perhaps there's a list showing what's there, but not identifying the role of each fuse?

I didn't see the inside of the lid myself, but I can't believe he would have made an effort to look on the internet if the information had been readily available. I'll take a look, presently—if there's a list with all the necessary info inside the box, I'll report it.

[steve2006]

This may help, fuse 46 engine bay box is for the horn but also states “Headlight Switch”

https://fuse-box.info/lexus/lexus-sc430-z40-2001-2010-fuses

[Ken Timbers]

Having removed the  relevant fuse, I thought there could be no further sound from the horn. Certainly the horn wouldn't work by pressing the button on the steering wheel. I set off this evening to get some petrol and was stunned to hear the horns blaring every few yards, worse than before! There seems to be a system that can by-pass the fuse box, presumably part of the immobiliser? I decided enough was enough and tried to pull out the connecting wires. They wouldn't move—probably haven't moved in 15 years—so I snipped them. I've got an appointment at Lexus on Thursday.

[Lexiguy]

Hi Steve

That's a great article with fuse box location and fuse information. I have copied it for future reference, I am sure it will come in!

Hi Ken

Sorry to hear the auto electrician wasn't successful with disconnecting you horn but it sounds like snipping the wires will have guaranteed success!

Ant

[Ken Timbers]

I took the car into Lexus (Sidcup) this morning (8 Sep) and collected it after lunch. I didn't get a chance to talk to the technician who did the work, so I can only report what I was told by the Service Dept team. The fault is thought to have been caused by a failure of the radar component, presumably part of the cruise control mechanisms. Apparently the radar component is no longer available, so could not be replaced. When I said it was important to me that the problem with the alarm system would not return, I was told that had been their aim, but it meant that the alarm system itself would be immobilised. I accepted that. So that's where it stands at the moment—and for Anthony's information, they reconnected the horn! There was no charge for any of this work.

I wonder whether that radar component is available in the US? I will do some research over the weekend, but if anyone has any knowledge of this, I'd be glad to hear.