Has anyone got advice on how to diagnose the fault with the least effort? The fault may have been there a long time as I rarely use the horn. I have checked the fuses and also can hear the relay click when the horn is pressed (so not the watch spring in the steering wheel assembly). I can't see any easy way to identify the wiring uner the hood and am reluctant to try to access the horns themselves which seems a lot of effort and it would seem unlikely that both horns would have failed.
W212 (2010) Horns don't work
- Thread starter greymonk
- Start date
Stratman
MB Enthusiast
You're right to think both horns are unlikely to fail together, so that leaves the wiring.
You can hear the relay click, so the low current side (switch button, relay coil) sounds OK. That leaves the high current side (relay switched contacts, fuse and wiring) as the likely culprit. Try changing the relay first, just because you hear it clicking doesn't mean the contacts are good. They can oxidise and develop high resistance, which is also true of fuse terminals and sockets. A pencil rubber is useful for cleaning dirty contacts, it's gentle abrasion will clean the surface without removing any plating or coating.
You can hear the relay click, so the low current side (switch button, relay coil) sounds OK. That leaves the high current side (relay switched contacts, fuse and wiring) as the likely culprit. Try changing the relay first, just because you hear it clicking doesn't mean the contacts are good. They can oxidise and develop high resistance, which is also true of fuse terminals and sockets. A pencil rubber is useful for cleaning dirty contacts, it's gentle abrasion will clean the surface without removing any plating or coating.
Thanks Stratman. I swapped the relay with another identical relay but it made no difference. I have tested all the fuses involved and all are OK. I can't think it would be the wiring but it is hard to get at any terminals to test them - it would be easy to find the problem if I could get to the horns and to see if the voltage is applied when the horn is activated but it seems quite a palava to access them. The wiring is also not easy to access or identify. I now suspect that it is the horns that have died as a broken wire is fairly unlikely. If you can think of any other approach it would be great.
- Joined
- Feb 22, 2010
- Messages
- 5,692
- Location
- Stirling, Scotland
- Car
- E55 AMG W211, E250 Sport W212, (and some Imps)
If I recall correctly there are two horns behind the bumper so likely a bumper off case to get to these but don't quote me on that.
I'd try and get to the source wire wherever this comes from and check for voltage.
Have you done a scan with Star or other?
Wouldn't be the first time a code has had to be cleared before allowing something to work.
I'd try and get to the source wire wherever this comes from and check for voltage.
Have you done a scan with Star or other?
Wouldn't be the first time a code has had to be cleared before allowing something to work.
Thanks Patrick. Yes bumper off at least, but I think it involves the inside wheel arches too. I will check again but I know it's a bit involved having watched a video of two blokes doing this job. I could not see an easy way of identifying and getting to the wires as they leave the fuse box; it's all very hard to access. I thought it would be easy to find the wires nearer the front but what wires I can see are taped up with others.
What is "Star"? I assume some sort of diagnostic software. I have not got any special equipment and actually not needed it much as the car has been very reliable and I've been its driver from new (about 96000 miles).
What is "Star"? I assume some sort of diagnostic software. I have not got any special equipment and actually not needed it much as the car has been very reliable and I've been its driver from new (about 96000 miles).
- Joined
- Feb 22, 2010
- Messages
- 5,692
- Location
- Stirling, Scotland
- Car
- E55 AMG W211, E250 Sport W212, (and some Imps)
Yes, I'd see if there is a local Indie or even someone on here with either Star or iCarsoft to get it scanned.
Hi Patrick. As the relay is clicking (steering the power) I think it is probably not being inhibited by any software in the car. I do use a good Indie for any repairs and annual service. I may well have them fix this if it involves a lot of dismantling as they've probably done it lots of times before. If it was a simple issue I would do it. But in any case, if I could provide some certainty as to the fault they could acquire the suitable parts (eg the horns) and it would avoid multiple trips (45 minutes each way) though they would lend me a car whilst repairs are done if needed. It needs a service and MOT in May so I could combine the jobs. Not having a working horn is an MOT fail anyway so must get it fixed by then.
Hello folks, wondering if you may be able to help please. i have a similar issue on my S212 T model. the high horn slowly died leaving the low working, now the low has also stopped, they both went quieter then nothing. i have checked the fuse and relay but to no perval i have also replaced the horns, guess what......still dead. i dont have star but have a icarsoft unit that is showing nothing on faults. i am slowly loosing the will to carry on. obviously the car is off the road as the horns are dead. odd that one died (went quiet and then stopped) then about a month later the other has done the same. please if you could offer any advice it would be great. i have both arches out so i can access the horns.
car is a 2011 S212 T model
many thanks
Colesy
car is a 2011 S212 T model
many thanks
Colesy
