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Discussion Starter · #1 ·
All, hoping for some help here.

I had a strange issue with the car. Will try to explain. About a month ago in the middle of the night the horn just started blaring. Car is parked in my driveway and had been sitting for hours. By the time I got to it after 10 minutes or so, the horn made a sick dying sound and went off. I got in the car anyway and fired it up. Car ran and drove fine, but no horn.

So, I just started digging into it. First thing to check was the fuse and sure enough it had popped. I put a new fuse in and the horn immediately started sounding and the fuse popped. Tried an even slightly higher rated fuse, same results, it popped after a few seconds. First conclusion is that one of the horns themselves is bad and pulling too much current, but that doesn’t explain the relay being on all the time.

I found an online wiring diagram that showed the relay for the horn. I did confirm that the relay is good and that it is being energized all the time. The wiring diagram shows it being controlled by the CEM under the glovebox. There are stories online of those being contaminated by water. I pulled this one out though and it is completely clean. No signs of ever being wet.

The CEM has an input that looks to go to the steering wheel module and then the horn contacts. I pulled the airbag out of the way and the voltage on the horn contacts is about 0.6V with the horn not pressed. I don’t know what the steering wheel module or clockspring module does with the horn signal but it it seems odd that the system would only put that low a voltage on the open horn signal which gets grounded when you press the horn. My suspicion is that whatever is between the horn contacts and the CEM is at fault.

My first question is whether any of the volvo documentation (VIDA) gives more in depth info on what is in the steering wheel module..

Here is what I found online:

https://www.manualslib.com/manual/533912/Volvo-C30.html?page=219#manual

I’m an Electrical Engineer by day and do a lot of analog and digital hardware design. I should be able to tackle this with the right info. I am going to continue to explore how the CEM horn input gets connected to the actual horn contacts through the steering wheel module or clockspring. Just wondering if anyone else has had a problem like this. I searched a number of C30, and S40 forums assuming all P1 platform cars have the same basic setup.

Regards,
Dave
 

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Discussion Starter · #2 ·
Good news, I got it fixed, or shall I say I had it fixed.

I was very very close to pulling the CEM and sending it out to xemodex. Looking over their website I saw that one of their affiliated shops wasn't too far from me on Long Island. I might have done that but I am in the middle of a local move and just didn't have time to do anything at this point. I was also at the point where it needed a NY State inspection and it wont pass without a horn.

Long story short, My original hunch mentioned below was correct. The steering wheel module was bad. The CEM was fine. If I wasn't so busy I would have sent the thing out only to not resolve the problem.

Mike at MB Automotive in Bay Shore got this fixed for me. There is just no way even with my electronics skills to figure this stuff out without the diagnostic tools.. Apparently the issue was intermittent and even they had the horns fire up in the middle of the night while they had it.

Just thought I would pass along the final result. Mike seems to really know his stuff and I would recommend them for any deep dive Volvo diagnostics if you are in the area.

Dave



All, hoping for some help here.

I had a strange issue with the car. Will try to explain. About a month ago in the middle of the night the horn just started blaring. Car is parked in my driveway and had been sitting for hours. By the time I got to it after 10 minutes or so, the horn made a sick dying sound and went off. I got in the car anyway and fired it up. Car ran and drove fine, but no horn.

So, I just started digging into it. First thing to check was the fuse and sure enough it had popped. I put a new fuse in and the horn immediately started sounding and the fuse popped. Tried an even slightly higher rated fuse, same results, it popped after a few seconds. First conclusion is that one of the horns themselves is bad and pulling too much current, but that doesn’t explain the relay being on all the time.

I found an online wiring diagram that showed the relay for the horn. I did confirm that the relay is good and that it is being energized all the time. The wiring diagram shows it being controlled by the CEM under the glovebox. There are stories online of those being contaminated by water. I pulled this one out though and it is completely clean. No signs of ever being wet.

The CEM has an input that looks to go to the steering wheel module and then the horn contacts. I pulled the airbag out of the way and the voltage on the horn contacts is about 0.6V with the horn not pressed. I don’t know what the steering wheel module or clockspring module does with the horn signal but it it seems odd that the system would only put that low a voltage on the open horn signal which gets grounded when you press the horn. My suspicion is that whatever is between the horn contacts and the CEM is at fault.

My first question is whether any of the volvo documentation (VIDA) gives more in depth info on what is in the steering wheel module..

Here is what I found online:

https://www.manualslib.com/manual/533912/Volvo-C30.html?page=219#manual

I’m an Electrical Engineer by day and do a lot of analog and digital hardware design. I should be able to tackle this with the right info. I am going to continue to explore how the CEM horn input gets connected to the actual horn contacts through the steering wheel module or clockspring. Just wondering if anyone else has had a problem like this. I searched a number of C30, and S40 forums assuming all P1 platform cars have the same basic setup.

Regards,
Dave
 
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