Engine stops....Horn sounds?

jimmy

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I have noticed a peculiar thing with my new car, if I stop the engine and take the key out of the ignition before the engine has fully stopped the horn will sound, the quicker you remove the key the longer the horn sounds??

If I wait till the engine has stopped (as you should) the horn doesnt make a noise!!

Never had this on the last car so it is quite odd, anybody else experienced it? Looking through the history and receipts that came with the car it had a new alarm box fitted not too long ago to fix a horn problem.

The alarm works fine, it goes off if you put your hand in an open window or open a door from the inside, and the alarm is a siren type not the car horn - I wonder if it is not related.

Would be usefull to know if anybody elses car does this.
 

GrahamC230K

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My engine stops instantly when I take the key out, so cant replicate that one!
 

Guy

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I have to ask, how much pressure are you under? Relax. Slow down! :D

I never was quick enough to beat the wick going out on the E300TD as far as I know, (horn never sounded) but Jimmy, I'll give it a go and let you know asap. :) But not tonight. :)
 

zerocool

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have seen ignition switches give problems,but never seen a case like this before
 
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jimmy

jimmy

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Originally posted by Guy
I have to ask, how much pressure are you under? Relax. Slow down! :D

I'm trying to slow down:)

I keep forgetting that I now have to wait a second or two for the preheater to work before turning the key to start!!

The horn only sounds if you stop the engine and turn it all the way back to 1st position, if you just turn the key one click to stop it doesnt sound.

How peculiar!!
 
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jimmy

jimmy

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Originally posted by Steve_Perry
Jimmy,

I presume the car manual says nothing about your new added feature?

S.

Didn't think of doing that.:p

I have been fiddling today, the engine does not have to be running for it to happen, with the ignition on (position 2), if I quickly turn the key through position 1 to 0 the horn beeps, do not even have to remove the key.

If I turn the key more slowly through position 1 to 0 it does not beep.

I know I will just have to turn the key a little slower to prevent it, I just wondered if anybody elses does it and why?
 

Sp!ke

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Just a thought - do you have an alarm/immobiliser on the car that activates the horn when triggered?

Factory alarm or aftermarket?

If so, I bet there is a second circuit (permanent live feed when ignition off) for the horn with its own separate earth connection used for the switch. If you turn the key too quickly, perhaps the relay for the main horn feed circuit is still momentarily closed (sticky relay) - the combination of the two open circuits (but live) bridge each other causing the horn to sound.


Thats my two pence worth but then again you prolly wont make much sense outta the above anyway.......I'll get my coat...
 
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jimmy

jimmy

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Spike,

Thats what I thought, but it is definetly a OE MB alarm unit, proper key fob etc. I tested the alarm by setting it with the window down and opening the door by reaching inside, the alarm is a siren type and not the car horn.

I have a load of old receipts that came with the car and one of them was to replace alarm unit to rectify horn fault!! Now I can't understand how the horn can be connected to the alarm if the alarm has it's own siren.

If it becomes a problem I shall have to look into it, I know a few auto electricians who maybe able to help, just thought it maybe a MB thing that somebody here might have known about.
 

Sp!ke

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Aha....car horn = backup for when siren is vandalised / disconnected etc....you got a bad earth somewhere matey.
 
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jimmy

jimmy

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Originally posted by Sp!ke
Aha....car horn = backup for when siren is vandalised / disconnected etc....you got a bad earth somewhere matey.

Funny you say that, I have just installed my amp and rear speakers that I had in my last car and I am getting interference from the alternator, there is a whistling noise that rises and falls with engine speed. Had it on the old car but not as bad.

I had been told that interference is usually caused by bad connections, earths in particular. Today I re-crimped and soldered all connections and terminals to and from the amp and speakers. I cleaned the battery terminals and the earth connections from the battery to the chassis, the interference is slightly less but still there. You can only hear it when the sound is turned right down.

So where is this bad earth likely to be? From the horn or the alarm? Where is the alarm???
 

Sp!ke

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My guess would be a bad earth for the alarm....thus finding its own earth through the horn somehow.

As to where the alarm is......I'm still old school Pirahna, so I haven't a clue.

On the subject of alarms and ICE, I once made up a very cheap but efficient immobiliser. I wired up the arial lead for the radio to a relay. the relay operated switched the low voltage feed to the coils. All the wiring was well hidden within the dash so from the engine bay, the only evidence was 'no-spark'. Basically, without the front panel for the stereo, the car was going no-where as the arial feed was not charged.

I always thought I could potentially market this as a kit form and the total sum of parts could be bought in at under a fiver....what do you recon? The only downside being that once the idea became known then johnny joyrider would know how to bypass the relay.
 

Guy

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Jimmy,

No matter how hard I try - silence. :(
 

fuzzer

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ok since no one else is replying to where the alarm is. Im going to make my guess public.

I think the alarm control unit is below the steel kickplate on the passenger side under the carpet.

Its three nuts and the plate comes away to reveal a box made by bosch i think.

I Dunno what it is , but , looks like a control unit of some sort.

Take the part number off the unit and phone the parts dept and get them to confirm what it is with you ;)

Its worth a try
 

Sp!ke

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Thats certainly where mine is kept but mine's aftermarket so I dunno.
 
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jimmy

jimmy

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My alarm unit is under the steel kickplate in the passenger footwell, mine is a Siemens unit, just a multi wire plug coming from it.

I have checked, cleaned and refitted all the earth connections I can find, most of them are conveniently placed under the bonnet on three separate points.

Managed to find the horns and clean and oil the connectors on them too, nothing appears to be wrong anywhere.:mad:

It seems to me that it is 'normal' for this car and may not be a fault. It appears that if the key is withdrawn very quickly from position '0' after being turned from position 1 or two the horn will beep, the quicker the key is withdrawn the longer the beep. Withdraw the key after a slight pause of about a second and no beep. I can repeat this time after time which makes me think it is not a fault as such.

The only thing I can think of is if it is some sort of anti hijack feature in case someone grabs the key through the window, but then the horn would need to sound for longer than it does.

I think Guy has got the answer, slow down, take a breath and take it easy..........chill.:cool:
 
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jimmy

jimmy

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Originally posted by Steve_Perry
Jimmy,

could it be a feature of MB diesels?

Still no mention in the car manual?

S.

I have read the manual(s) cover to cover and no mention, no mention in the Haynes manual either. (Refitting is a reversal of the above. hehe:p good old Haynes manual!)
 

zerocool

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how about going to the dealership and asking them,the ignition swicth on later mercs is a sort of control unit which uses can lines rather than 12v,it sort of sends signals to control units rather than sending power.
 
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jimmy

jimmy

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Definetly a fault!!:devil:

I have concluded that this is a fault, sometimes it does it sometimes it doesnt.

I took it to my local MB dealer expecting them to say bring it in two weeks on Tuesday and we will have a look and take your arm and leg too. I was pleasantly surprised that the service manager actually came out to the car to witness the problem and agreed it shouldn't do it, he suggested that the voltage maybe low and to try a new battery. The battery on the car is smaller in size and capacity than the one that was on the C180 and did not have A/C.

He suggested I buy a bigger battery from them, try that and if that didn't fix it, to bring it back in for further investigation. So I went back to work and fitted the right battery and guess what?

The horn still peeps at may.:confused:

This evening I took the phono cables out from the passeger side and put them down the drivers side away from the main power cable to try and stop the alternator whine that comes through the rear amp and speakers. This cured the alternator whine but now there is a constant low level buzz only when the ignition is on.

I also noticed that the rear washer pump runs when the interior fan is switched on!!! Checked with a voltmeter and the pump is getting 1.5volts when the fan is on. The rear wiper does not function properly either.

It would seem that there are some gremlins in the electrics. I phoned the bloke where I bought it and he knew about the horn but thought it was a feature of imported cars, he couldn't explain the washer pump or noise interference though.

Anyway, luckily the car came with a (hopefully) comprehensive 12 month AA warranty and it can be taken to any garage including MB to be fixed.:bannana: :bannana:

So I am hoping it will all be fixed without any cost to me.
 

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