P38A Stupid horn

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RatCav

RatCav

Member
Posts
48
Location
Preston
Hi there. Been searching for a while for answers but nothing definitive.

I have a phantom horn issue. Central locking works fine with the key/button.

Horn works if you press it.

Good (new) battery.

Changed the steering wheel coupler.

Changed the horn relay.

Taken the wheel off and cleaned/adjusted the buttons to make sure they don't short.

Horn has a mind of its own.

Now for the oddity. Today while looking it was switched off and the horn was silent. Shut the bonnet and the horn blipped. Stood there for a couple of seconds. Shut the car up and locked the door. Went to walk away and then the horn went off. When it goes off it won't stop unless you pull the fuse/relay.

I tried looking for a bonnet switch for the alarm but couldn't find anything.

Starting to do my nut in. Added complication there isn't anyone local that I trust (Preston) with a diagnostic. Short of having my arm ripped off by the Dealer.

Any ideas.
 
As much as I can get to easily. All looks good so far. Was wondering if there was anything obvious I have missed before I start having to rip panels off. Hate electrics.
 
have you checked the wires on the horn behind the grill? Are these activated by a live or negative signal? Presuming there are two wires too it...o_O
 
Yup .. two wires fed from the BECM via a fuse and relay apparenty
 

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Looks like there is a +12v that feeds the relay on two pins. One goes to the BECM and then on to the steering wheel switches. When you press the button it earths the feed allowing the relay to energise and then supply the feed to the two horns.

I am going to assume it goes via the BECM to register a fault if the BECM doesn't get a +12v feed from the relay and flash a message. It doesn't flash a message, well it hasn't for the last couple of months with the fuse (F41 engine bay) removed.
 
Horn is set as lock indicator and alarm sounder. Blip when you shut bonnet is mislock. Bonnet switch is on O/S bonnet locking catch. You should be getting bonnet open on dash message centre when ignition is turned on. If bonnet switch or any other lock shows no lock when alarm sets horn will sound. Yeah some untrustworthy people with diag in Preston.
 
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Hi Wammers

Would you say the cause of my issues is the bonnet locking catch then? As I am driving it is jiggling and setting the horn off. Have to admit I haven't noticed a warning message .. mind I am concentrating more on the fact the horn is blaring for no reason and annoying everyone.

Also do you yourself have a diagnostic, or know someone who does? Would be very appreciated if you could point me in the right direction for this.

Cheers
 
RatCav said:
Hi Wammers

Would you say the cause of my issues is the bonnet locking catch then? As I am driving it is jiggling and setting the horn off. Have to admit I haven't noticed a warning message .. mind I am concentrating more on the fact the horn is blaring for no reason and annoying everyone.

Also do you yourself have a diagnostic, or know someone who does? Would be very appreciated if you could point me in the right direction for this.

Cheers
Click to expand...

Can't be sure but there must be a mislock somewhere. I have Nanocom for the diesel. Some say the BECM on the petrol can be accessed with the diesel unit but to be honest i don't know that is can.
 
Reading this thread is ringing alarm bells. I've seen this so many times where as soon as the battery is connected the horns blows until you disconnect again. This fault usually comes with the headlights on as well.

Unless the horn itserlf has shorted out, I place my bets on the becm has developed the fault.
 
wammers said:
Can't be sure but there must be a mislock somewhere. I have Nanocom for the diesel. Some say the BECM on the petrol can be accessed with the diesel unit but to be honest i don't know that is can.
Click to expand...

There is only one way to find out :D The car is off down south for a week. When it gets back would it be possible to see if your Nanocom can talk to the BECM at least. Will put some monies your way for the privilege.

Rick-the-Pick said:
Reading this thread is ringing alarm bells. I've seen this so many times where as soon as the battery is connected the horns blows until you disconnect again. This fault usually comes with the headlights on as well.

Unless the horn itself has shorted out, I place my bets on the becm has developed the fault.
Click to expand...

Going by the wiring diagram the only way for the horn to get a live feed is if the BECM lets it. so either the BECM is some how getting a signal to tell it to arm the horn (via a short, alarm circuit, locking circuit??) or another circuit is shorting out onto the horn line post BECM. Obviously not being too familiar with the P38 I could be completely wrong :D
 
RatCav said:
There is only one way to find out :D The car is off down south for a week. When it gets back would it be possible to see if your Nanocom can talk to the BECM at least. Will put some monies your way for the privilege.

Can have a look i suppose. May talk to it in BECM diagnostic mode
Click to expand...
 
RatCav said:
Thats brilliant. Will get back to you when it returns. Many many thanks for your time so far.
Click to expand...
Hiya mate, I have nanocom for thor petrol models but it's in Czech republic at the moment. If you haven't sorted it by the time mine comes back then no problem to have a look.
 
Awesome Wazzajnr!

I will probably replace the o/s bonnet catch and do some wire tracing. Failing that I feel it is diagnostic time. Holding out a slim hope it isn't new BECM time.
 
RatCav said:
Awesome Wazzajnr!

I will probably replace the o/s bonnet catch and do some wire tracing. Failing that I feel it is diagnostic time. Holding out a slim hope it isn't new BECM time.
Click to expand...
Rick the pick should be able to sort it if it's the BECM.
 
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