Horn MOT Fail

[Roland]

Sounds like a stupid question but can anyone advise where the horn relay and/or fuse is on my 1995 GT - assuming they exist? I can't find any mention in my manual or in the Volvo wiring diagrams.

The horns themselves check out OK - I've tested them off the car with a power probe and got a good loud sound on both. The obvious next step is fuse/relay. But where are they ?

I've checked out all the posts on here including Jim's checking procedure.

Can anyone illuminate me ?

[glasgowjim]

fuse number 8 which is 20 amps on 94/95 cars

[Roland]

Thanks Jim.
Just went out to garage to check fuse 8 (at 11.10pm and raining) and right enough - it does say horns - amongst other stuff - on the fuse box cover.
Must have a blind spot because I've checked that cover several times.
However, the fuse looks OK.
So is there a relay somewhere ?

[Ben Harris]

Thanks Jim.
So is there a relay somewhere ?

There is, but it's not very easily accessible. It's soldered inside the CEM - or it certainly was on the older 480's with the original CEM's. I assume the CEM III (which is what a 95 will have) has the relay inside it too.

Does the alarm work? That will help diagnose if the problem is the horn signal going into the CEM, or if it's the signal coming out of it.

Ben.

[Roland]

Oh dear ! I hope I don't have to replace the CEM.

The security on the car is a basic immobiliser - no alarm. It was on the car when I bought it 5 years ago and preferable I think on older cars. Alarms in my experience are a pain in the butt.

However, that doesn't help very much.

On one of my other cars (Porsche 924S) the horns were earthed through the steering column via the horn ring. Depressing the horn pad completed the earth circuit - or was supposed to. Over time the steering column lost it's earthing capability due to build up of dirt, grease etc at it's base (so I was told by the Porsche specialist Strasse). What they did was to drill a hole in the steering outer column below the dash and run an earth wire to the metal support of the dash. This did the trick and is still in place 10 years later.

Does the 480 suffer from this problem ? Or what are the other likely possibilities ?
This car is an airbag model. I haven't checked the horn ring connections yet.

[Ben Harris]

My reason for asking about the alarm is that all 480's have a basic alarm built into them from the factory, controlled by the CEM. It works on the principal that if you lock the car from the drivers door (not sure about passenger), the alarm is activated (can't remember if it's activated straight away or after a minute). Then, if any of the doors are opened from the inside (test this by leaving the windows down) the horn sounds. I also think the CEM activates the alarm if it detects a high current drain from anything too.

The horn on the 480 is switched via earth through the steering column in a similar way you describe. The only difference being that the earth signal is fed into the CEM which in turn activates an internal relay and sounds the horn. As the relay is controlled by the CEM, this also allows it to sound the horn if it needs to for the alarm.

On my very original 480, the long-range driving lights circuit (also controlled via the CEM for the 'driveway lightup function') had gone faulty and would flicker on/off while the car was locked, causing a current drain. This in turn caused the CEM to activate the alarm. As a result of this, the previous owner had had the horn rewired through a relay, and completely bypassed the CEM. I sourced a replacement CEM, and repaired the connections that had been bypassed.

From memory (this was about 8 years ago!), the horn earth switching wire was a green or brown wire directly under the steering column and was quite obvious to see which one it was coming the back of the steering wheel. This was on an '89 car though, so no airbag. Any airbag wiring will be yellow, so be very careful with any yellow wires!

Ben.

[Roland]

Thanks Ben that's useful information.

I did try leaving a window open and opening the door from the inside just to make sure there was no alarm. The immobiliser is an Aftermarket product (Laserline) fitted in 2002 by Halfords (according to the PO's records passed on to me). So like yours it looks as though the original Volvo alarm, (and possibly CEM relay), was defective and has been bypassed.
I'm now wondering whether the horns are wired through a standard relay. If so it would make life easier. As a matter of interest I've had a battery drain for ages (see previous post), which is through fuse 7, but have been unable to pin it down to any component protected by that fuse. A dodgy relay in the CEM might be a possibility. (Or it might be a complete red herring.)

Anyway, Fact 1 - the alarm is not being activated by the CEM. Fact 2 - the horns have worked from the horn pad OK for at least the last 5 years - upto this last MOT.

I shall investigate the horn push/ring/earth tonight to see whether there are any issues there.

[glasgowjim]

Can supply a working CEM 3 if needed

[Roland]

Thanks JIm,
Will take you up if I can't sort it otherwise.

[Roland]

Had the steering wheel off today to have a look at the horn contacts.
Horn wiring, terminals and contacts look OK.
Not sure about the spring loaded piece that goes through the steering boss and contacts with the circular metal track on the slip ring. Do these wear out?
The spring feels robust enough but the contact point must be in continuous rubbing contact with the slip ring every time the steering wheel turns.
Not knowing what a good one should look like it's difficult to tell whether mine is u/s or not.
The VADIS parts diagram is particularly useless, as is my local Volvo dealer who said the only technician likely to know about the 480 was holiday for a fortnight.
Any contributions gratefully received ?

[Roland]

Jim,
Have sent you a pm.

[glasgowjim]

pm sent in return.

[Roland]

For anyone interested, have sorted my horn problem.
Took off the airbag steering wheel and remade all connections I could find.
Sprayed everything with electrical contact cleaner.
Replaced wheel and - bingo - horn works loud and clear.
Not sure which bit is dodgy, but I suspect the spring loaded contact on the clock spring.
If so, it's only likely to be a temporary solution but if it gets it through the MOT that's fine.
Very rarely use the horn anyway.