Another ABS1 saga

[donstauffer]

I'm trying to troubleshoot an ABS 1 system on a 92 K75S. The original symptoms were both lights flashing (abs and brake) in unison at about 1 hz. Resetting the system fixed it for about a month, next time for about a week, next time for about a day, now the system won't reset.

Blink code decoded to #7, controller. Found a unit on ebay, same results.
Using the troubleshooting info by Brian Curry, I'm pretty confident in the following:

1) Batt voltage good, 12.6V. 1 yr old BMW battery
2) Wheel sensor resistance just as listed in the troubleshooting guide.
3) Relay coil resistance OK.
4) Both modulators show resistance different than the posted value. From the ABS connector, pins 6-10 and 9-10 both show open for the front, and 7-12 and 11-12 show open on the rear. It seems unlikely that both modulators would fail.

5) Relay socket pin 87 to ground measures about 440 ohms instead of the indicated 17K.

I'm not sure if the resistance variance is significant. I've either got a system problem unrelated to the controller, or two bad controllers. I wish I had a way to test the controllers so that I had a known-good starting point.

Any suggestions? I'd like to restore the ABS function if I can, and I hate to give up on a technical issue like this without a fight.

 

[deilenberger]

I'd suggest emailing Brian directly with the numbers - he may have some ideas.

PM me and I'll send you his email address..

 

[wndsrfr]

Please keep us posted.....

on your progress as you tease out the cause of the problem. I have a '92 K75RT with a failed ABS system similar to yours. Brian and Mick both provided a great amount of help in the troubleshooting and I also purchased a "known good" controller which didn't fix the problem. Hate to say it, but I finally abandoned the fight and enjoy riding with great manual brakes. Would be nice to have the ABS, but would really prefer to update the system as these are getting really old and the failure mode isn't pretty---like complete loss of braking on the rear for me--lucky it was the rear and not the front!

Good luck!

 

[donstauffer]

Can you give me some details regarding your troubleshooting process or error codes?

I'm learning a lot, unfortunately it's a pretty old subject to be studying, fixing a 15 year old bike with ABS that's two generations dated...

 

[pfls]

I would suspect both the control units. These are prone to failure, and ebay is full of people selling junk parts.

 

[wndsrfr]

Oh boy.....

that's stretching the memory beyond the elastic limit and it looks like the series of posts/threads that were in the website about 3 years ago are gone....

I followed Brian's posted guide on IBMWR as you have and used the Radio Shack LED to read the codes. The first mode of failure was no rear brakes and the rear modulator got hot to the touch after about 5 minutes of operation. The code read that the rear modulator was bad, so I got another from Beemer Boneyard which was good. However, the codes then went to bad control unit, so $400 later and with a good control unit the system actually worked for about 20 minutes, then "bad control unit" again. That's the point that I quit active troubleshooting and started into the next phase....

I sent the "good" control unit to Victor Rocha in California to see if he could repair it--no dice with him. Next it went to the "Module Master"--Gavin Curtis and after six months he sent it back saying he couldn't fix it. All of this was last year, so maybe either of them has had some sort of epiphany since then and can now salvage a control unit....I don't know.

So, I'm riding with manual brakes, as I have all of my life prior to the K75 purchase, so I'm no better off or worse off than if it didn't have ABS to begin with, other than the $$ sunk in hunting a fix. What we really need is a retrofit of ABS-2 generation systems to the ABS-1 bikes......anyone ready to tackle that one??

Regards,
John

 

[PHILRUP]

ABS fault

ABS gear ring teeth intact?
This may be too simplistic.