Please help!! Rain, hail, an abandoned wedding and broken car...

[bluejmc2005]

Evening all,

I have had a nightmare. I was at a wedding from 11.30 today, at 7.30 (literally as the first dance is beginning) I get frantic calls from my teenage daughters. The car - my 2010 CLS350 - is making a horrendous sound and they cant stop it. They say it started after a particularly strong rain/hail shower. Alarm I assume, but no its clear that its the horn. I talk my eldest through unlock/locking, putting ignition on, nothing stops it, neighbors out complaining- my wife and I have to live our dear friends wedding to get home. When I get home, sure enough the horn is continuously going, coming from front passenger side. ****ing down with rain so I cant make out where it is other than the general area. Nothing I do with the car stops it, aside from disconnecting the battery - which I do to stop neighbors lynching me. I check the fuse diagram, find the horn fuse and remove it (under the bonnet) reattach the battery - no horn. Marvelous, seems the rain has shorted the horn I think. But no, umpteenth error messages appear on the car, SBS,ABS and everything else. Maybe the battery was drained by the horn, causing these electrical gremlins? disconnect battery, leave it 2 minutes, reattach - no errors come up on display. start the car, and drive it for 30 mins to charge the battery - with a large emergency fete horn we happen to have in case of emergency. Come home, pull up, try to turn the car off - no - wont turn off, key will come out, display still on, car wont turn off. plug in my icarsoft and get 12 error codes P1111 unbdefined, p0111 P0135 P0130 P0030 P1102 P0102 P0100 U0101 U0155 P1102 P0102. I remove the 2nd big fuse from the back of the fuse box under the bonnet to kill the car engine, does its job. Disconnect battery. leave a few mins, reconnect battery, error codes all gone, lock car. Come here hoping a wonderful person will take pity on me and offer some suggestions or solutions. PLEASE HELP!!

Thanks,

Jason

 

[Uncle Benz]

Sounds like water in a front SAM unit, probably from a blocked drain

 

[Frontstep]

These cars are tested with a lot of water but if it can't get out then the problems start so above seems a good start, and its better to find out now with some maintenance than have it happen on some grumpy winters night.

 

[bluejmc2005]

Thank you all for your replies. I stepped away from the car last night as 1 - it was dark 2 - it was torrential rain and 3 : I'd had a fair amount to drink!

I'm trying to work on the principle that the simplist solution is usually the correct one. There were no issues with the car that I knew of prior to the heavy rain. It rains heavily, issues begin. The alarm was not triggered, just the horn. In fact when I first returned home the car seemed to be unaware there was an issue with the horn and was working quite happily save the horn. I'm yhetfore going to begin with the assumption that the horn shorted/got wet and that caused the continuous noise. I've removed the fuse for that and the horn ceased. Now, the rest of the issues perplex me; could it be that whilst removing said fuse in my haste to prevent the neighbours rioting I was not as careful as I should have been and water got inyo the fuse box under the bonnet? Possibly, whilst my wife held an umbrella as I did it I know from experience that mere drops of water can cause havoc with electrics so the first thing I'll do later this morning when the rain stops is remove each fuse from th fuse box and make sure all are dry. Battery is already disconnected as I wanted to prevent any further damage. After I've done that, I'll check all the drains (if I can find a chart of where they are in my 2010 CLS) and then I'll find the actual horn itself and see if that provides any clues. I'll update here with any success or failure
Again thank you so much for your help and please do keep the ideas coming!

 

[Frontstep]

If it's dry where you are open the bonnet have a good look for water paths in muck then let the sun in to dry things out, find your drains there's no harm in cleaning them only good.

Open up everything you opened to inspect and dry.

 

[Tony Dyson]

Thank you all for your replies. I stepped away from the car last night as 1 - it was dark 2 - it was torrential rain and 3 : I'd had a fair amount to drink!

I'm trying to work on the principle that the simplist solution is usually the correct one. There were no issues with the car that I knew of prior to the heavy rain. It rains heavily, issues begin. The alarm was not triggered, just the horn. In fact when I first returned home the car seemed to be unaware there was an issue with the horn and was working quite happily save the horn. I'm yhetfore going to begin with the assumption that the horn shorted/got wet and that caused the continuous noise. I've removed the fuse for that and the horn ceased. Now, the rest of the issues perplex me; could it be that whilst removing said fuse in my haste to prevent the neighbours rioting I was not as careful as I should have been and water got inyo the fuse box under the bonnet? Possibly, whilst my wife held an umbrella as I did it I know from experience that mere drops of water can cause havoc with electrics so the first thing I'll do later this morning when the rain stops is remove each fuse from th fuse box and make sure all are dry. Battery is already disconnected as I wanted to prevent any further damage. After I've done that, I'll check all the drains (if I can find a chart of where they are in my 2010 CLS) and then I'll find the actual horn itself and see if that provides any clues. I'll update here with any success or failure
Again thank you so much for your help and please do keep the ideas coming!

A car's electrics don't work like that anymore, the front SAM unit mentioned above works like a big box of fused relays, much like a PLC in industrial applications where sensors and switches provide input signals, the SAM (Signal Acquisition/Activation Module) then evaluates those signals, communicates with other modules and switches various outputs on or off so your horn is switched on/off from a SAM output hence the suggestion you have water ingress in the front SAM unit rather than elsewhere.

 

[bluejmc2005]

The SAM unit it housed with the fuses under the bonnet I think? I have this morning inspected the fuse box area, I cant see any evidence of water ingress etc. I started the car this morning to no error messages, it powered down as it should, I drove it briefly (no horn) again powered down as it should. I looked at the horn, nothing obvious but seems reasonably simple to bolt on and off. Put the fuse back in for the horn, tried the horn and worked 2 our of 7 times, the other times it tried to make sound but failed. So I think the horn needs replacing. I have removed the fuse for it again and will order a replacement horn, wont drive it until that arrives. I cleared all the water escapes I can see, as I say the one above the fuse box was clogged everywhere else seemed fine no evidence of water anywhere

 

[Doug1234]

Would this year of car still have two horns , one high tone and one low tone ?

 

[joderest]

well, a horn normally has either a live feed which is switched, on in some circumstances an earth that is switch, not sure what Mercedes do, anyway, they can draw quite a bit of power. You do not say how long it was sounding for, but looks like hours, hence the battery would have been well down on power and perhaps caused all your other issues (its know that the brand do not like batteries down on power)
My suggestion, for what it is worth is yes, change the horn as possibly shorted out, but whilst waiting for it, fully charge the battery, and then check it keeps its charge.
How old is the battery, perhaps its time for a new one anyway.

 

[Tony Dyson]

well, a horn normally has either a live feed which is switched, on in some circumstances an earth that is switch, not sure what Mercedes do, anyway, they can draw quite a bit of power. You do not say how long it was sounding for, but looks like hours, hence the battery would have been well down on power and perhaps caused all your other issues (its know that the brand do not like batteries down on power)
My suggestion, for what it is worth is yes, change the horn as possibly shorted out, but whilst waiting for it, fully charge the battery, and then check it keeps its charge.
How old is the battery, perhaps its time for a new one anyway.

A quick and easy test to confirm whether any vehicle's horn works by conventional wiring feeds and switches or is controlled by a CAN Module is to press the horn and listen for a momentary delay in the response of the horn sounding, I had the use of a VW Passat not long ago and the delay was so significant it wouldn't sound on a 'fast repeat thank you pip, pip'.

 

[bluejmc2005]

well, a horn normally has either a live feed which is switched, on in some circumstances an earth that is switch, not sure what Mercedes do, anyway, they can draw quite a bit of power. You do not say how long it was sounding for, but looks like hours, hence the battery would have been well down on power and perhaps caused all your other issues (its know that the brand do not like batteries down on power)
My suggestion, for what it is worth is yes, change the horn as possibly shorted out, but whilst waiting for it, fully charge the battery, and then check it keeps its charge.
How old is the battery, perhaps its time for a new one anyway.

brand new - changed when I bought the car a few weeks ago, sounded for a good 75-80 minutes