Horn blowing by itself

pete4pool

Hello all, 
I have a 2006 volvo s40 and few months ago while I was in bed with the car locked on the drive, I heard the horn of my car going off. As it was late at night and half my estate was looking out at me, I took out the fuse to stop it. 
I put it on the back burner and few days before the nct I put the fuse back in and it wasn't going off, until I was driving to the nct and it start small bursts. Luckily it behaved itself during the nct and it passed. Again I took the fuse out as it started going off again. So its been that way for few months. I went to tackle it this weekend and put the fuse back in, but now it is constant. I removed the grill and each horn (one at a time) to see if it was one of them causing it. But as both are going off, I am saying the actual horns are fine. 
Now I am looking at the steering wheel, pushing the whole centre part triggers the horn. I am thinking that the airbag part and the horn button must be too close or something. But when I push it, it does not feel weak, it feels that I need to push it all the way. And if it were the spring behind it, it would not come back up. 
So before I take off the airbag part of the steering wheel, I am looking for other Ideas where the problem may lie? 
This happens even when the car is locked and turned off with no key. 
I don't have any other electrical problems.
Haven't found any known issues with the volvo for this. 

Thanks,
Pete

scannerd

have a look at the wiring diagram below, page 86 is the horn, its controlled via a steering wheel module, goes to central electrical module and then to a horn relay.

you problem could be any of these, possible it could be wiring but as it need power it less likely its a short.

I would work back from the horn, checking the control signal at the relay and testing the relay operation (swap with one that is the same) - i'd be guessing thats where your problem is.



http://www.volvowiringdiagrams.com/volvo/S40%20V40%20V50%20Wiring%20Diagrams/TP3990202%202006%20S40%20V40%20Wiring%20Diagram.pdf

pete4pool

Thanks, thats great info, very useful doc to have. Diagram looks abit too much for me though. 
Talked to a mech and he thinks it may be related to the immobilizer. Going to try the relay and if thats not it, take it to the garage. 
Thanks.

com1

Happened to me with an 06 V70 - it was the alarm / immobilizer. Strangely enough reseating the fuses and changing the battery fixed it for me...

pete4pool

Thanks com1, I have had a few issues with the alarm / battery. Since the last time I changed the battery, indicators don't blink when I lock the car and the leaving a phone or laptop in the car will set off the alarm, even when there are no calls/messages/etc sent to the phone/laptop. 
So wonder if it maybe related to the battery. 
Do you know if the immobilizer can be disabled easily. Might try to get the mech to test a new battery.

com1

Sorry, I don't know whether or how easily the immobilizer can be reset switched off or otherwise.


It was a few years ago. I remember finding that the 12v cigar lighter port(power source) in the boot as it was leaking power (a short somewhere?), which I think was the primary cause of the drain on the battery. Actually this may have been the reason the alarm started to act up (they may have been valid alarm activations due to the power drains). Anyway I swapped the battery and just pulled the fuse for the 12v point - I didn't use it so didn't want the bother of chasing wires through the body of the car to check where the problem was I had enough of that with the tailgate

Ah the memories. I really liked that car, even with all its foibles

dr.fuzzenstein

Now you can never again say that you are not one to toot your own horn...:)

my3cents

OP Check how the bonnet (and boot) fit and lock, its possible either are just sitting on the sensor micro switch so that as the car cools done the bonnet moves slightly and the alarm gets triggered

case_sensitive

com1 wrote: »

.. I remember finding that the 12v cigar lighter port(power source) in the boot as it was leaking power (a short somewhere?), which I think was the primary cause of the drain on the battery. Actually this may have been the reason the alarm started to act up (they may have been valid alarm activations due to the power drains).

This was a thing with my Alfa 159 too; I had a wifi ODBII reader plugged in and it drew enough power to cause serious upset to the electronics; which are very sensitive to low voltage, they drop off as the power becomes unavailable. Mine was coupled with a charging problem caused by a rusty earth strap (x2). Cleaning up the earth point and copper wiring solved the issue, and I unplugged my OBD reader when not it use, haven't had it since.

http://www.alfaowner.com/Forum/alfa-159-brera-andamp-946-spider/999545-inertial-switch-intervened.html#post15249073

The first time it happened, the first thing to go was air con, then traction control, ABS, then the cooling fan, then the windows (!). On one of the hottest days of the year. Thankfully it's grand now.