BMW K bikes (Bricks)

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George R

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Hi - as you my realise from previous posts, I have a 1996 K75RT which I have been slowly getting back into shape ( medical problems etc.- me as well!) but this problem has got me stumped. The bike has ABS but when the ignition is switched on and the two brake levers are pressed, the triangle lamp fails to go out. Checked all the ABS Brain and reset it and the ABS goes through the checks correctly and does not show any fault code. Next I changed all the bulbs and the short wiring harness to the tail bulbs but there was no change. Finally I removed the ABS Brain and the two blue relays, tested, then substituted the Bulb Monitoring Unit, but there still was no change - the lamp stays on after the brake levers are operated.

Any help with this would be greatly appreciated.

    

Inge K.

Inge K.
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Hi George!
If your tail light function as normal, and the brake light functions when each of the
of the levers is pressed...one at the time...the problem must be in the BMU relay.
This is valid if the warning light stays on solid, and not flashing.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

MikeP

MikeP
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Obvious question (sorry):

You are riding it (or at least rolling it far enough for the test to complete)?

    

Inge K.

Inge K.
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When I did read the post the first time, I didn't see that you did substitute the BMU relay.

If the warning lamp stays on also when the relay is removed...you probably have a
sort to ground... 1. in the wire between the relay socket and the instrument cluster....
2. in the wire between the ABS ECU and the instrument cluster...
3. internal in the instrument cluster.


__________________________________________________
Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

Rick G

Rick G
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MikeP wrote:Obvious question (sorry):

You are riding it (or at least rolling it far enough for the test to complete)?

You need to get to 2.5mph/4kph for the test to complete.


__________________________________________________
"Man sacrifices his health in order to make money.
Then he sacrifices money to recuperate his health.
And then he is so anxious about the future that he does not enjoy the present; the result being that he does not live in the present or the future; he lives as if he is never going to die, and then dies having never really lived."   Dalai Lama


Bikes 2004 K1200GT 1998 K1100 LT, 1986 K75 GS.
    

George R

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Hi Rick - sorry - but this does not apply when the ABS Brain and the relays are removed.

I think I may have the answer but am waiting for Motorworks to send me some kit try to find out if my thoughts are correct.

Watch this space - might be a couple of days before the post arrives.

Thanks to all who have replied.

    

commanderdrako

commanderdrako
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I am a newbie so pardon my ignorance. I thought that the triangle light will only blink or stays on if there a busted light or light that is going bad. Is it related to the ABS too? Does it blink if there is any problem with the bike too?


__________________________________________________
1992 K100RS
VIN 6494041

2009 Aprilia Tuono
1985 Yamaha Maxim X (sold)
    

George R

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Hi there - Yes it most certainly does.  The triangle warning lamp is connected to the Bulb Monitor Unit (BMU) which is a type of relay with eight wires attached to it so as you have gathered it has a lot of functions. If the red lamp stays on when ignition switch is turned 'ON', stays 'ON' when both brakes are operated, whether or not the ABS
initialises, and whether or not the Brain and the 2 relays are removed, then the first thing to do is clean thoroughly all the wiring comnections (especially the earths) to the lamps, then change the stop, tail and pilot lamp bulbs because, even if working they can fault the BMU even if the bulbs are lit. If no change, find someone local with a brick and swop your MBU for the other and vice versa.  This will check out your BMU.  If you need to get one 2nd hand - buy two on sale or return as they can be faulty. I had four before I got a fifth one to work correctly. I think if the donor bike is written off, the crash probably ruins the motherboard inside.

The BMU also shows if there is a fault in the ABS system, the forum has a lot of information about this and the proceedure to check. I spent a lot of time ripping out and replacing both lighting and ABS components until I found that the core problem was the BMU. It is also connected to and checks the fuse holder, the ECU via the water temp sensor on the block and indirectly to the ignition module, and there are also feeds and returns through the ABS Brain.  I did not explore any further into the wiring as I had managed to find my fault and was most happy that when the BMU was replaced and the ABS reset, the ABS Brain came back to life and initialised correctly.

To sus this out I took the Clymer Manual and copied the wiring diagram for the ABS (both K75RT and the ABS1 K1100) blew them up to A3 then laminated them so that I could write on them with a Chinagraph pencil. This was essential whe tracing the wiring paths ( Use a black and white diagram -you can see the lines better).  Once you have done this you will see that the cabling does not just go to a particular sensor or lamp etc but will probably carry on to further lamps or sensors, so that the BMU probably checks virtually all the electrical system on the bike.

Another point - on the Non ABS bikes - there is only the one white/blue wire from the BMU to the triangle lamp - there is obviously no wire to the Brain.  This means that the checking proceediure for the non-ABS bike is the same -but obviously the Brain has no part in complicating the checking operation.

I hope this is is of use to you. I was probably lucky that my ABS  Brain had not succumed as well, but I could certainly say that it kept my mind active in the garage last
winter. Brrrh!!.

Please get in touch if you have further queries.

Regards



Last edited by George R on Sun Jun 23, 2013 12:34 pm; edited 1 time in total

    

commanderdrako

commanderdrako
active member
active member
George R wrote:Hi there - Yes it most certainly does.  The triangle warning lamp is connected to the Bulb Monitor Unit (BMU) which is a type of relay with eight wires attached to it so as you
have gathered it has a lot of functions. If the red lamp stays on when igniton switch is turned 'ON', stays 'ON' when both brakes are operated, whether or not the ABS
initialises, and whether or not the Brain and the 2 relays are removed, then the first thing to do is clean thoroughly all the wiring comnections (especially the earths) to the lamps,
then change the stop, tail and pilot lamp bulbs because, even if working they can fault the BMU even if the bulbs are lit. If no change, find someone local with a brick and swop
your MBU for the other and vice versa.  This will check out your BMU.  If you need to get one 2nd hand - buy two on sale or return as they can be faulty.
I had four before I got a fifth one to work correctly. I think if the donor bike is written off, the crash probably ruins the motherboard inside.

The BMU also shows if there is a fault in the ABS system, the forum has a lot of information about this and the proceedure to check. I spent a lot of time ripping out and replacing
both lighting and ABS components until I found that the core problem was the BMU. It is also connected to and checks the fuse holder, the ECU via the water temp sensor on
the block and indirectly to the ignition module, and there are also feeds and returns through the ABS Brain.  I did not explore any further into the wiring as I had managed to find
my fault and was most happy that when the BMU was replaced and the ABS reset, the ABS Brain came back to life and initialised correctly.

To sus this out I took the Clymer Manual and copied the wiring diagram for the ABS (both K75RT and the ABS1 K1100) blew them up to A3 then laminated them so that I could
write on them with a Chinagraph pencil. This was essential whe tracing the wiring paths ( Use a black and white diagram -you can see the lines better).  Once you have done
this you will see that the cabling does not just go to a particular sensor or lamp etc but will probably carry on to further lamps or sensors, so that the BMU probably checks
virtually all the electrical system on the bike.

Another point - on the Non ABS bikes - there is only the one white/blue wire from the BMU to the triangle lamp - there is obviously no wire to the Brain.  This means that the
checking proceediure for the non-ABS bike is the same -but obviously the Brain has no part in complicating the checking operation.

I hope this is is of use to you. I was probably lucky that my ABS  Brain had not succumed as well, but I could certainly say that it kept my mind active in the garage last
winter. Brrrh!!.

Please get in touch if you have further queries.

Regards



Very informative! Thank you!


__________________________________________________
1992 K100RS
VIN 6494041

2009 Aprilia Tuono
1985 Yamaha Maxim X (sold)
    

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