After a lot of diagnostics I have found the reason for my inoperative ABS on my 1992 K100RS is the AB02.5 ABS ECU. Their seems to be a lot of info about fault finding but nothing on the actual repair. Being a little electronic minded and having done some fairly intricate repairs on some very expensive circuits, I opened the ABS ECU and was greeted by some very old school circuitry and components. Without doing some very extensive fault finding has anyone found what is the most common or likely item on the board/s that has failed?

Thanks
SC

Get onto Tosi here http://bmwk10075abs1fix.web.fc2.com/ he is a wizz on the early ABS.

They also appear up on eBay. I picked up one recently for £50 and it works fine. 2.5 units are fitted to K100 16v, K1 and early K1100's.

Just saw this

https://www.ebay.co.uk/itm/1993-BMW-K1100LT-K-1100-LT-ABS-MODULE/143308196294?hash=item215dd589c6:g:1pkAAOSw-M5dEha0

Is it worth fitting second hand.
I have no ABS light showing only the bulb warning light.

I assumed from your first post you had tried to reset and had also checked the codes and had proved unit was faulty. Normally the abs light flashes or stays on even with a faulty ecu. Have you checked the abs relay - one of the blue ones - if this is removed the abs light will not work.

Thanks I will check

I have two spare relays in a spare bulb and fuse box on my bike.
What does the abs relay look like?

Thanks
SC

The ABS relays are a Blue colour.

Some information here about the relays

https://www.motorworks.co.uk/vlive/Shop/Parts.php?T=5&NU=10&M=40&Ct=KA&SbCt=BA_10_40_KA_40

No neither of these is an ABS relay
One is a Mini Relay and the other may be a fuel injection.
All are Black

Have you got blue relays fitted in the relay box ? These are sometimes removed to stop the light flashing.

This will tell ya where it should be

The blue relay is still there and hasn't been removed.
What other things will cause the ABS light not to work?

SC

Have you checked the bulb , these can also be removed by previous owners.

 I have 4 bikes with this abs unit and I never saw the bulb not working, usually the opposite when it would not go out.

 One bike did have the bulb removed from the speedo console when I initially got it.

The bulb is working as I have checked this twice now.
Although one of the bulbs is missing but this is not used (the yellow one on the rev counter).
All the bulbs are good and the connection is clean.

SC

I just checked one of mine. If I completely disconnect the ABS ECU the Abs light comes on solid when I switch on the ignition.

 I must assume the ECU sends a signal to switch off the bulb. Maybe this will help with your troubleshooting.

No ABS ECU fitted = Red ABS light on solid

My ABS light is not illuminated wether the ECU is plugged in or not.
No matter what I do I cannot get the ABS light to illuminate.

SC

I haven't done intricate repairs on expensive circuitry but when I encounter a relay that isn't doing what I expect it to do, I smack it with the handle of a screwdriver. If that doesn't change its attitude, I replace it.

It looks like extensive fault finding is becoming your only option, or consulting with Tosi which has been recommended previously.

I agree with Laitch that the next step is to 'check' the relay as it controls the bulb.

OK I will remove the relay and test it.
Is their a wiring diagram available for this bike?

SC

Take a look here

http://www.kforum-tech.com/electrical/k100rs-ABS-electrical-schematic.jpg

OK I tested the ABS Relay and it is working but no ABS light.

But on further investigation the Load Shedder relay had been removed.
After reinstalling this the ABS Light is flashing when the ignition is turned on and remains on when running.
Should I try reseting and testing the ABS ECU as with this disconnected parts of the ECU probably were not working?

What are the procedures does the ABS light turn off once moving?

Cheers
SC

heyskull wrote:. . . does the ABS light turn off once moving?

The moto must be moving for the test phase to be completed. Here are instructions from the BMW ABS manual.

Thnks for that will test later.
I will reset it before I try.

If I remove the Blue Relay the ABS light still flashes is this correct?


SC

heyskull wrote:If I remove the Blue Relay the ABS light still flashes is this correct?

Leave the relay alone. Take the moto for a ride. If it can't be ridden now, don't concern yourself with it until you can get it rolling. Be certain the sensor gaps are set correctly and that the battery is in excellent condition before moving off.

Laitch is correct, take the bike for a ride. 

There is a procedure for reading and clearing faults through the three prong diagnostic plug located under the seat.  I've had several faults with the ABS on my bikes, and every time it was caused by a low battery voltage, so make sure your battery is fully charged and working properly. 

After that, check the wheel sensors for proper gap, and then all the blue four pin ABS system connectors.

I have been for a ride on the bike tonight (Keswick and home).
ABS light is still flashing unless you press the ABS button when it will go out for 10 miles and come back on. Battery is in as new condition holding good charge and charges well. When I try to reset and then read the codes it still comes up with 7 flashes which states ABS ECU fault. No other faults show but if I guess the ECU has a fault it will not read any others?! Is this looking like I should either look for a working ABS ECU or send my own of to get repaired?

SC

I have a faulty unit that does the same - 7 flashes. I picked up a replacement on ebay. So spare or repair looks like the next step.

OK I have got another abs ecu. It now reads no faults doing the flash test.
On turning the ignition on I get a flashing ABS light and solid warning light. If I press both brakes the warning light starts to flash with the ABS light also flashing.
As I pull off the warning light goes off but the ABS light is now on constantly.
I feel I am very near to getting this working again...
Any further help would be appreciated aa I cannot find what a solid abs light means?

Thanks
SC

I have had a little ride on it and it feels like the rear abs is working. I don't think I'm brave enough to find if the front is working!!!!
Just to confirm the abs light is on constantly, is this correct to say it is working correctly?

Just to confirm the abs light is on constantly, is this correct to say it is working correctly? 

No.

Once you set off you should hear the clunk from the ABS modulator as it finalises the pull away test. Then both lights should extinguish.

Are you sure both front and rear brake levers operate the brake light and that the rear running light is also working.

Mike

Yes all the lights are functioning correctly.

Where is the modulator sited?

On a further note. Once the bike is moving and the abs light is on constantly you cannot turn it off with the abs button.

Thanks

Where is the modulator sited?

ABS1 - It's the big canisters either side of the bike by the rear footrests.

ABS2 - It's a single canister mounted just in front of the coolant overflow tank (viewed from the left side of the bike).

Have you seen the following information?.

ABS versions and fault display

ABS1

ABS1 was only used on K75, K100, and 1993 K1100LT. It's recognizable by the modulator units mounted to the footpeg plates. A fault is indicated by the ABS light and the bulb monitor flashing in unison. The bulb monitor will be on continuously until the system has verified operation of both brake switches and both bulb filaments (taillight and brake light) and then it extinguishes and becomes the second ABS light. The primary ABS light (and the monitor light, once its test is complete) will flash in unison until the bike moves off. If they continue to flash in unison after that, there is a fault. You will probably get a fault #7 upon startup after you have left the battery disconnected for a period of time. 

Resetting:

(mostly from the IBMWR tech pages)

Resetting ABS1

• Locate the diagnostic connector on the right frame rail, under the seat. Remove it from the blanking plug.
  
  
• Insert one end of 20 cm wire into the middle socket of this connector.
  
  
• Ground the other end firmly to a metal bolt in the area (and keep grounded).
  
  
• Hold the ABS button down as you turn the ignition on. You should see the lights flash together as normal. 
  
• Keep holding the ABS button down for about 8 seconds. The ABS light will stay on solid. 
  
• Release the ABS button.
  
  
• Turn off ignition, remove wire. 
  

Fault Codes

ABS1 and ABS2 fault codes

Info on diagnosing ABS1 and ABS2 faults is described by Brian Curry in great detail on the IBMWR K-tech pages. In a nutshell, by putting a readout light between the ABS pin and ground you can get a blink code when the bike is on. All codes except 5 seem to be persistent (needing reset by this procedure). There is also a BMW document, part 01 71 9 798 811 (5/90), that you may be able to locate which is for troubleshooting ABS.

• 1. front pressure modulator
  
  
• 2. rear pressure modulator
  
  
• 3. front wheel speed sensor
  
  
• 4. rear wheel speed sensor
  
  
• 5. battery voltage too low
  
  
• 6. ABS relay
  
  
• 7. ABS control unit
  
  
• 8. sensor gap front or rear, or other outside influence
  
  
• 9.
  
  
• 16. reportedly "Failed plunger test" (also seems to be persistent)
  
  

I have reset this but the abs light does not go solid. Would it be a good idea to disconnect the battery for 10 minutes and reconnect and reset and see if it works? Is their any videos showing how this should work and the noises it makes testing?

SC

Sorry I am stuffing to send a picture.
On turning the ignition on the ! In a triangle is solid and the light next to the fuel light with ABS through it is flashing. On firing it up and pressing both brakes the ! In a triangle light flashes and so does the abs light. On putting into gear and moving off the ! In a triangle Light goes off and the abs stays on permanently (not flashing).

Sorry that is the best I can explain. No noises or clunk's from the modulators and no faults showing on the flash test. All bulbs are correct and working as they should.

SC

What does a constant abs light mean? I am showing no faults on the flash test but getting no noises from the modulator.
On a further note, when initially turning on the ignition from the relay box you can here the test relays ticking. But after about 5 seconds their is what sounds like a relay that is either faulty or struggling as it makes a sparking noise. I have removed and checked the contacts on the abs and the load shedder relay and both look in as new condition.

SC

Hi Heyskull

I had issues with a solid ABS light on my k100.

If you read my post dated 2015, it will give you an idea of the complex nature of the beast,

but  dont give up.

The main thing I learned was to test the fault code first before resetting the system.

I got one flash for the front modulator, which was faulty,  but after resetting , I consistently 

got seven.
 
If I remember correctly from "Tosi",  7 flashes covers a multitude of faults, not just the "Brain "

On one occasion I got "no flashes"  ,but the bulb then came on during riding, and stayed on.

My front Modulator resistance was low according to info from "Tosi",

so I swapped it with another unit which gave a higher  reading, and my system has been reliable 

ever since.

Of course yours is the later system, but when I  got different codes before and after resetting

the "Brain", and I suffered the light staying on even with no fault codes showing, I began to 

mistrust the fault code system somewhat.

Good luck.

Bob

I am getting the same no fault codes. If I plug the old one in it flashes seven times, which is the abs ecu fault.
Is their a video available to show how this sets up and makes noises testing itself?

SC

Where is the plugs for the modulators?
How do u test the modulators?

Any further help on this problem?

The best info is on Tosi's site  I gave a link back in post 2. You can email him directly he is very helpful.

Hi Heyskull

This an email I sent to Tosi..

 Dear sir, 
My k100 ABS brain fault code  is showing one flash.
I have tested the ohm resistances across ABS connector pins 6-9 are 2.8k ohms
                                                                                                           6-10     0.97k ohms
                                                                                                            9-10    2.84k ohms  for the front modulator
would this confirm to you that my front modulator is bad.

Tosi agreed the low value on pins 6-10 was low
 
so I bought a spare unit from e bay which showed more consistent values, and my 

system has worked since.

I agree with Rick, contact Tosi , he got back to me very quickly.

Bob

Bob between 6 9 I have 4.43
Between 6 10 I have nothing
Between 9 10 I have nothing.
This is testing the plug.

Sx

Your readings seems to indicate  a fault, but I am no electrician.

I assume yours is the early 16v with the same modulators as the k100.

I cannot find my email from Tosi giving details  of which ABS pins to check for each modulator, 

but someone on the forum might know.

But you do need to contact him

www.k100abs@gmail.com


Bob

My ecu is the later ab02.5 one