The horn by the heater blower won't stop!

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songzunhuang
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The horn by the heater blower won't stop!

Post by songzunhuang »

Driving on the freeway on the way back from work this evening, my car's horn started to blare. I immediately pressed the horn button thinking something must be stuck, but I could hear the horns beeping when I pressed the button in the steering wheel.

I pulled over and shut off the car, but the horn was still blaring. Opening the hood I realized that the sound was coming from the horn at the base of the windshield by the cover for the squirrel cages for the blowers. If I pressed my horn button on the steering wheel, the horns behind the grill would beep. Well I disconnected the battery to stop the horn and then I removed the cover for the squirrel cages and disconnected one of the leads for the horn. Reconnecting the battery, I drove the rest of the way home. Note: the trip computer showed 4 dots and after I set the time, it was fine.

When I got home, I reconnected the horn with the car off and there was no sound. However, when I put in the key and turn the ignition switch (position 1 or 2), the horn begins to blare again.

What the heck is going on? Why is my car so horny now? ;)

Ah, never a dull moment with this car...
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1984 633CSi
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Brucey
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Post by Brucey »

that horn is part of the built-in security system (as described in the owner's manual, controlled by the OBC).

Take a look at the wiring diagram, and you will find that the third horn is controlled by a relay. Chances are that the relay is faulty.

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Post by Pod »

Just leave it disconnected :D
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Post by wattsmonkey »

Chaps, you've saved me a red-faced "What is this for?" question! I was wondering why there was a mysterious horn which never appeared to honk.

A horn honks next to the squirrel cage, but nobody hears it...
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Post by Pod »

wattsmonkey wrote:A horn honks next to the squirrel cage, but nobody hears it...
Like one hand clapping :lol:
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Post by songzunhuang »

Brucey wrote:that horn is part of the built-in security system (as described in the owner's manual, controlled by the OBC).

Take a look at the wiring diagram, and you will find that the third horn is controlled by a relay. Chances are that the relay is faulty.

cheers
Brucey, is this the relay K2 in the fusebox or is this one under the driver side dash that I hear about but have no idea what it looks like.

BTW - I bought the Bentleys book, but no owners manual yet. Odd thing is that after my battery disconnect and then horn disconnect, I reconnected the battery and the OBC is working fine. No sign of an issue, just that crazy horn if I plug it back in.


I was majorly annoying while I was driving and trying to get off the freeway. It must have blared for like 5 minutes. Oh, great fun.
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Post by baders »

Song do you have the Electrical Troubleshooting manual ? If not, you really should download it :) It is available through links here on BC somewhere.

The Onboard computer relay is under the left hand side dash. There may well be a problem with your on board computer relay, but the relay in turn is driven by the OBC itself. Make sure you have no security code set in the OBC. If THIS were the case however, you would not be able to start the car, as this relay also has contacts to drive the main relay. Highly likely it is the on board computer horn relay gone U/S though. Edit. Note; I am looking at my 1986 ETM, not sure that the 1984 633 is the same
Last edited by baders on Wed Nov 11, 2015 12:25 am, edited 1 time in total.
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2002 E46 M3 / Topaz Blau Metallic / Black Nappa / 6 speed SMG software tuned / Bilstein PSS10 Coilovers / CMP RACP reinforcement
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Post by baders »

1986 635csi LOCUTUS / Arktis Blau Metallic / Pearl Beige / S38B36/ Close ratio dogleg 5sp
2002 E46 M3 / Topaz Blau Metallic / Black Nappa / 6 speed SMG software tuned / Bilstein PSS10 Coilovers / CMP RACP reinforcement
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Post by songzunhuang »

baders wrote:Song do you have the Electrical Troubleshooting manual ? If not, you really should download it :) It is available through links here on BC somewhere.

The Onboard computer relay is under the left hand side dash. There may well be a problem with your on board computer relay, but the relay in turn is driven by the OBC itself. Make sure you have no security code set in the OBC. If THIS were the case however, you would not be able to start the car, as this relay also has contacts to drive the main relay. Highly likely it is the on board computer horn relay gone U/S though. Edit. Note; I am looking at my 1986 ETM, not sure that the 1984 633 is the same
OK, is it obvious which one it is? I can't look at it tonight, but would be nice to know it's a black 5 prong relay or something. I have downloaded the ETM, but that doesn't mean I understand it all! LOL!

I do not have a security code set. The car appears to drive just fine and I can even use the OBC to get time, temp, range, etc and all is well.

Can I just change the OBC horn relay instead of the entire unit? From the looks of things, the entire computer unit is really pricey!
Last edited by songzunhuang on Wed Nov 11, 2015 6:40 am, edited 1 time in total.
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Post by songzunhuang »

Thank you for the links.
The RealOEM price for the unit is laughable! $1200 bucks? Uh, no.

Functions in my OBC all seem to work, except for the blaring horn (which is disconnected now). Can I just replace a relay instead of the entire unit?

I hear the relay is under the dash on the drivers side and possible in the OBC itself. I don't suppose someone has the diagram for the OBC main unit circuits do they?
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Post by baders »

The on-board computer control box is separate to the OBC display itself, and can be replaced. The relay in the control box itself I don't know. If you are brave it looks as though you can pull that control box apart. By doing this you may be able to replace or repair the actual faulty relay. If, as you have indicated, there are no other OBC faults, I would be just leaving that horn disconnected.

If you really want it fixed though a bit of fault finding will be required. Firstly you will want to know if there is a short to ground on the wire going from the horn to the relay contacts. If there is no short then the relay is almost certainly U/S...........back to being brave...........or replace the whole box.
1986 635csi LOCUTUS / Arktis Blau Metallic / Pearl Beige / S38B36/ Close ratio dogleg 5sp
2002 E46 M3 / Topaz Blau Metallic / Black Nappa / 6 speed SMG software tuned / Bilstein PSS10 Coilovers / CMP RACP reinforcement
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Post by songzunhuang »

baders wrote:The on-board computer control box is separate to the OBC display itself, and can be replaced. The relay in the control box itself I don't know. If you are brave it looks as though you can pull that control box apart. By doing this you may be able to replace or repair the actual faulty relay. If, as you have indicated, there are no other OBC faults, I would be just leaving that horn disconnected.

If you really want it fixed though a bit of fault finding will be required. Firstly you will want to know if there is a short to ground on the wire going from the horn to the relay contacts. If there is no short then the relay is almost certainly U/S...........back to being brave...........or replace the whole box.
I will be brave! I looked at the wiring and it appears to be fine. There was no sign of damage in the portion that goes from the horn to where it passes through the firewall and disappears into a loom.

I'll take a look inside the OBC box and see if I can make anything out. Im guessing a relay shouldn't be too hard to spot. I've already opened up the main OBC once to replace the fuse (which repaired an inoperative OBC) when I originally got the car.

Question for the forum is if there is a relay inside the main OBC (aluminum box) itself or if there's another plug in type relay on the area outside of the box under the dash?

Again, I'd go look but with this daylight saving time, its so dark when I get home and kind of cold outside that I am just going to wait until the weekend to deal with this. Still, it's great to gather all the knowledge I can before I have to deal with it.
Thanks.
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Post by sansouci »

To those electrical gurus: if the relay was faulty, there would still be low amperage running through it causing the high amperage contacts to close. While the horn itself was disconnected, would it contribute to battery drain?
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Post by baders »

Not necessarily Ken. The contacts on the relay may simply be welded closed. This is a fairly common occurrence.

Song, I imagine the relay is on board the OBC control box, not separate. If you pull it apart, make sure you take lots of photos to add to our fantastic BC knowledge base ! :D
1986 635csi LOCUTUS / Arktis Blau Metallic / Pearl Beige / S38B36/ Close ratio dogleg 5sp
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Post by songzunhuang »

baders wrote:Not necessarily Ken. The contacts on the relay may simply be welded closed. This is a fairly common occurrence.

Song, I imagine the relay is on board the OBC control box, not separate. If you pull it apart, make sure you take lots of photos to add to our fantastic BC knowledge base ! :D
I will. It's so confusing. I see things advertised as a OBC relay, but the picture looks like the entire module. And then there's prices. I've seen it from $40 to $1280. It just seems to me that this area is not one that is explored throughly.

Also, if a relay fails, I would be surprised if it fails in the closed position (causing the horn to sound). Normally relays are open and when they get magnetized, they shut (closing the circuit). So what I have read doesn't all make sense to me still.

I'll continue to explore and post pics if I actually go that route.
Incidentally, I drove the car to work today and the OBC is not operational again. It was fine the last time I drove it after the horn blaring incident. The backlight is fine, just the red LEDS are not lighting up like they used to. This just adds further mystery to all this.
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Post by baders »

Picture this scenario. For whatever reason, at some stage the OBC horn operated. The relay coil energised and the contacts close. For whatever reason (worn contacts, shorts, over-current), the contacts at that stage carried excess current and welded shut. The OBC horn relay coil would have de-energised but the contacts are still welded shut. Now every time you connect the OBC horn it goes off.

As far as identifying the module, best to pull it and check the number.
1986 635csi LOCUTUS / Arktis Blau Metallic / Pearl Beige / S38B36/ Close ratio dogleg 5sp
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OK, My Car did not have this part!

Post by songzunhuang »

So I was doing more research on the OBC relay as suggested by several replies. I have come to the conclusion that my car (1984) did NOT have an OBC relay.

Searching on REALOEM for part number 65 81 1 373 726 results in a part that started with the 1985 635CSi. http://www.realoem.com/bmw/enUS/partsea ... 5811373726

Here's another search on eBay for this where you can see a fitment guie. No 1984 633 on the list. http://www.ebay.com/itm/BMW-e23-e24-e28 ... T5&vxp=mtr

I'm thinking that my relay must be in the OBC main computer.
Anyhow, I'll crack it open this weekend and see what I can see. Meanwhile the car is driving just fine (with the horn OBC disconnected) but the OBC LEDs are no longer lit. :(
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Re: OK, My Car did not have this part!

Post by Pod »

songzunhuang wrote: Meanwhile the car is driving just fine (with the horn OBC disconnected) but the OBC LEDs are no longer lit. :(
If that bothers you, just reconnect the OBC and disconnect the horn, as I suggested the other day :P
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Post by baders »

Song, the link I posted before was a search 633>1984>USA>Instruments, measuring systems>On Board Computer reveals part number 65811372823 that is pn 2 here; http://www.realoem.com/bmw/enUS/showpar ... Id=62_0065
1986 635csi LOCUTUS / Arktis Blau Metallic / Pearl Beige / S38B36/ Close ratio dogleg 5sp
2002 E46 M3 / Topaz Blau Metallic / Black Nappa / 6 speed SMG software tuned / Bilstein PSS10 Coilovers / CMP RACP reinforcement
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Post by songzunhuang »

baders wrote:Song, the link I posted before was a search 633>1984>USA>Instruments, measuring systems>On Board Computer reveals part number 65811372823 that is pn 2 here; http://www.realoem.com/bmw/enUS/showpar ... Id=62_0065
Thanks for the info. I did check out that information. That part#2 is the main control module. I replaced a fuse in that a while back and it made my OBC come alive. It worked for a month or two, before this new horn issue popped up.

What I'm flummoxed about right now are the comments about replacing a OBC relay. That part#2 is NOT just a relay. It's the main brains of the OBC.

Perhaps there's a relay inside that main control module that controls the horn. I don't know at this time. This is what I must explore more.
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Re: OK, My Car did not have this part!

Post by songzunhuang »

Pod wrote:
songzunhuang wrote: Meanwhile the car is driving just fine (with the horn OBC disconnected) but the OBC LEDs are no longer lit. :(
If that bothers you, just reconnect the OBC and disconnect the horn, as I suggested the other day :P
The horn is disconnected right now and that's the state it's in while I am driving it to work this week. The OBC itself was never disconnected (just the horn). Odd thing is that the OBC itself was working a few days ago (while the horn was disconnected), but it's not anymore. The red LED screen is blank.

If I have time this weekend, I'll dig into this some more. I'm in information gathering mode right now.
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Post by baders »

OK I've had a bit more time to look into this. The circuitry is different between say my '86 635 and your '84 633. In the '84 633 ETM below. you will note that there is an "On Board Computer" and an "On Board Computer Control Panel". We need to find out what is actually what. My feeling is that the latter is the display panel on your dash, and the former is the part I linked above. If so, the OBC horn is driven by the above box. Is anyone able to confirm this ?
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1986 635csi LOCUTUS / Arktis Blau Metallic / Pearl Beige / S38B36/ Close ratio dogleg 5sp
2002 E46 M3 / Topaz Blau Metallic / Black Nappa / 6 speed SMG software tuned / Bilstein PSS10 Coilovers / CMP RACP reinforcement
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Post by baders »

Referring to the above diagram, look for the box with a C1 plug (there should also be a C2 plug) and a brown/yellow wire going to pin 17, that be your culprit. Indeed, this box http://www.ebay.com/itm/NEW-OEM-BMW-658 ... 1554229734 has two plugs :D
1986 635csi LOCUTUS / Arktis Blau Metallic / Pearl Beige / S38B36/ Close ratio dogleg 5sp
2002 E46 M3 / Topaz Blau Metallic / Black Nappa / 6 speed SMG software tuned / Bilstein PSS10 Coilovers / CMP RACP reinforcement
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Post by songzunhuang »

baders wrote:Referring to the above diagram, look for the box with a C1 plug (there should also be a C2 plug) and a brown/yellow wire going to pin 17, that be your culprit. Indeed, this box http://www.ebay.com/itm/NEW-OEM-BMW-658 ... 1554229734 has two plugs :D
Thanks guys. You've confirmed what I suspected thus far. The panel is definitely the thing in the dash with the buttons and LED display.

The main control unit has the 2 plugs, just like the picture you linked to on eBay. It was this unit that I removed a while back and replaced a fuse, which resulted in everything turning on and working for about a month.

The current behavior has got me really confused. I've noticed a few odd things.

1. When the LED display is NOT working, turning power on via the ignition switch will result in a chime that I swear is coming from the display. The display doesn't work, I just hear a chime that I've never heard before.

2. On the way home today, the LED panel turned on again! I set the time to 7:33pm and it was fine for about 2 minutes. Then it shut it self off again. What?

I thought that the dead display may have been my fuse again, but the fact that it came on for a few minutes kills that theory.

Meanwhile the ETM scan shows something interesting. The OBC horn is clear on the left (upper part in the picture), However there's another thing at the lower left labeled as an "Alarm Horn Control". What that? I can't tell from the diagram if it's a separate part of if it's part of the main control unit. Any ideas?
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This photo was taken only about 1 minute apart. Note the LED is completely dead in the upper picture. All of a sudden, it came on (lower picture) and I set the time. Literally 2 minutes later, it went out again. What is going on?
This photo was taken only about 1 minute apart. Note the LED is completely dead in the upper picture. All of a sudden, it came on (lower picture) and I set the time. Literally 2 minutes later, it went out again. What is going on?
Screen Shot 2015-11-12 at 9.20.31 PM.png (1.35 MiB) Viewed 9695 times
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Post by baders »

songzunhuang wrote:
baders wrote:Referring to the above diagram, look for the box with a C1 plug (there should also be a C2 plug) and a brown/yellow wire going to pin 17, that be your culprit. Indeed, this box http://www.ebay.com/itm/NEW-OEM-BMW-658 ... 1554229734 has two plugs :D
Thanks guys. You've confirmed what I suspected thus far. The panel is definitely the thing in the dash with the buttons and LED display.

The main control unit has the 2 plugs, just like the picture you linked to on eBay. It was this unit that I removed a while back and replaced a fuse, which resulted in everything turning on and working for about a month.

The current behavior has got me really confused. I've noticed a few odd things.

1. When the LED display is NOT working, turning power on via the ignition switch will result in a chime that I swear is coming from the display. The display doesn't work, I just hear a chime that I've never heard before.

2. On the way home today, the LED panel turned on again! I set the time to 7:33pm and it was fine for about 2 minutes. Then it shut it self off again. What?

I thought that the dead display may have been my fuse again, but the fact that it came on for a few minutes kills that theory.

Meanwhile the ETM scan shows something interesting. The OBC horn is clear on the left (upper part in the picture), However there's another thing at the lower left labeled as an "Alarm Horn Control". What that? I can't tell from the diagram if it's a separate part of if it's part of the main control unit. Any ideas?
Song, separate Alarm Control Horn is in fact part of the OBC. It is just a way of representing better in the electrical diagram, but it's all in the same box.
1986 635csi LOCUTUS / Arktis Blau Metallic / Pearl Beige / S38B36/ Close ratio dogleg 5sp
2002 E46 M3 / Topaz Blau Metallic / Black Nappa / 6 speed SMG software tuned / Bilstein PSS10 Coilovers / CMP RACP reinforcement
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