I wrote this post before.

So, a month ago I bought a brand spanking new lead acid battery, and literally nothing changed.

The brand new battery holds 12.6 volts in the morning. The moment the engine starts and is on idle, it jumps to 13, the moment I even slightly touch the accelerator it jumps up to 13.5 or 13.7. within roughly 5 minutes of riding the voltage slowly raises to 14 volts, and is at 13.4 at idle RPM.

In the morning I usually clear the ABS fault from the day before (if it's not cleared already) and start my bike. It calibrates perfectly fine, and the ABS works flawlessly. After 10-15 minutes of riding it calibrates again, and it does so without fault. After roughly 35-50 minutes of riding, the fault appears.

The fault shows up on average once a day - most days it happens once (on my way home), some days it works flawlessly, some days the fault shows up twice (on my way to work, and back home). I usually try restarting the fucker anywhere from 2 to 5 times, and each time the moment the wheels start spinning the fault shows up again. If I really need ABS and don't mind being extremely late, I park the bike for 20-30 minutes to cool down, and the fault usually clears, but sometimes (like 15-20% of cases) still persists. But, if it appears in the morning, it always successfully clears the error and calibrates after I leave work 8 hours later. Like I said in my previous post, engine temperature doesn't matter - I can leave the bike stationary with the engine running until the fan kicks on, or I can ride at constant speed cooling the engine, the ABS will fault after 35-50 minutes regardless.

It's always either a 6 (battery) or a 7(brain) error, although 7 shows up slightly more often, probably a 70/30 split.

I've tried electrical contact cleaner on the Motronic multi-pin connector, and then wiggling it around, with mixed results - sometimes it helps for 2-3 days, sometimes it does absolutely nothing. I tried cleaning every pin, once with a toothbrush, and once with high grit sandpaper, and it made absolutely no change whatsoever.

I'm not sure what to do next.

What is your VIN Number?

92KK 84WW Olaf wrote:What is your VIN Number?

0188436

Close to mine. ABS 2.

But my voltages are higher, on start up and idle and my battery voltage at rest is also higher.

Low voltage can cause ABS issues.

I have had new batteries go faulty and maybe you should get the battery checked, also the charging voltage. Mine is over 14 volts.

92KK 84WW Olaf wrote:Close to mine. ABS 2.

But my voltages are higher, on start up and idle and my battery voltage at rest is also higher.

Low voltage can cause ABS issues.

I have had new batteries go faulty and maybe you should get the battery checked, also the charging voltage. Mine is over 14 volts.

That's something I was considering...

My battery is lead acid, is there a battery type that holds a higher voltage?

No. I'll try and clear up a bit of a misunderstanding about 12 volt batteries here. There are six cells in each battery, but each cell produces 2.4 volts (not 2.0 volts). So, a fully-charged good battery will read 14.2 volts the moment you take it off charge. This is called the 'surface charge'. Overnight that will drop to between 12.6 and 13.2 volts, so on the face of it your battery is okay. However, that is off-load. The moment you turn the bike on, if the battery is not brilliant then the  voltage can drop well below 12.6 volts. A crude test would be to put a voltmeter on the battery while cranking the engine, but a better test would be to get a local repairers to do a proper load test. Lead-acid batteries have a finite life; if you get more than three years you're doing really well. AGMs (advanced glass mat) are much better. The one in LFB is coming up to its tenth birthday but it does get a 50+ mile journey almost daily which is good for any battery.

If you can stand the maths/chemistry I've just found this:

https://batteryuniversity.com/learn/article/how_to_measure_state_of_charge

Dai wrote:No. I'll try and clear up a bit of a misunderstanding about 12 volt batteries here. There are six cells in each battery, but each cell produces 2.4 volts (not 2.0 volts). So, a fully-charged good battery will read 14.2 volts the moment you take it off charge. This is called the 'surface charge'. Overnight that will drop to between 12.6 and 13.2 volts, so on the face of it your battery is okay. However, that is off-load. The moment you turn the bike on, if the battery is not brilliant then the  voltage can drop well below 12.6 volts. A crude test would be to put a voltmeter on the battery while cranking the engine, but a better test would be to get a local repairers to do a proper load test. Lead-acid batteries have a finite life; if you get more than three years you're doing really well. AGMs (advanced glass mat) are much better. The one in LFB is coming up to its tenth birthday but it does get a 50+ mile journey almost daily which is good for any battery.

If you can stand the maths/chemistry I've just found this:

https://batteryuniversity.com/learn/article/how_to_measure_state_of_charge

In that case I'm not sure what I can do. he battery itself doesn't have a year printed on it, but when I got it it was in a pristine box that looked absolutely brand new, and I was the very person that poured acid in the cells. So I'm assuming my battery is as new as it can be.

Just for you, I went out late at night and started the bike.


At the very startup the battery drops down to roundabout 10 volts, but immediately picks itself up. Each time I revved (roughly 2k RPM each time, so nothing crazy) the engine, the idle voltage increased visibly, so it would have been near the top in no time.

Also the voltmeter I installed in the bike doesn't agree with this, and tells me the voltage was 12.5 before startup, and 12.8 after I started the engine. The voltmeter is connected to the car charger port near the radio, while I put my oscilloscope leads straight on the battery contacts. I'm guessing either my oscilloscope isn't calibrated, or the 50 cent tiny voltmeter on the bike isn't accurate.

Fault codes for ABSII

• 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
  

Count the dips that is when the led goes off not the flashes.
When the fault shows while riding turn the key off then back on while still moving and if the fault corrects then battery voltage is at fault.

RicK G wrote:Fault codes for ABSII

• 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
  

Count the dips that is when the led goes off not the flashes.
When the fault shows while riding turn the key off then back on while still moving and if the fault corrects then battery voltage is at fault.

I'm counting the LED coming on, or in other words I'm counting every rising edge, so the number I end up with is the same.

I've read somewhere that 6 was low battery, and 7 was the control unit... Guess I was wrong, but to be honest my google-fu isn't good enough to find a reliable source of those error codes.

The fault doesn't clear when turning the key. I have to short the test pin to ground and hold the ABS button for a few seconds to do that, every time.

How probable is it that it's actually the relay that needs replacing? The bike is 25 years old after all...

Doing it that way you will count the light coming back on in readiness for the next code and you get one more than it actually is. The normal state for the light is on.

StefanMajone wrote:
I've tried electrical contact cleaner on the Motronic multi-pin connector, and then wiggling it around, with mixed results - sometimes it helps for 2-3 days, sometimes it does absolutely nothing. I tried cleaning every pin, once with a toothbrush, and once with high grit sandpaper, and it made absolutely no change whatsoever.

Though this could be a matter of misinterpretation, the Motronic has not much to do with the ABS. The ABS brain is the vertical FAG assembly against the battery.

StefanMajonez wrote:
I've read somewhere that 6 was low battery, and 7 was the control unit... Guess I was wrong, but to be honest my google-fu isn't good enough to find a reliable source of those error codes.

Try these links.
http://bmwk10075abs1fix.web.fc2.com/
http://bmwk10075abs1fix.web.fc2.com/ABS2-repair1.html

RicK G wrote:Doing it that way you will count the light coming back on in readiness for the next code and you get one more than it actually is. The normal state for the light is on.

I do count the light coming back on, but I strongly disagree I will count one more than there actually is.

I made this real quick, blue is counting dips while red is counting the LED coming on. same number.



So the most probable culprit is the battery (or voltage in general), but why does the ABS fault after I've ridden for over half an hour, charging the battery along the way?

StefanMajonez wrote:

This reading can be quite honestly disregarded when it comes to the exact measurement. I hooked up two multimeters and the readings don't agree.


This morning the reading was 12.5. Ignition and all lights on, it dropped to 12.25, fuel pump brought it down momentarily to 12.1. The very moment of startup is questionable because the multimeters only measure roughly twice or three times per second, but one dropped to 10.9 and another to 11.2 volts.

And then it was running at idle at 12.2 volts. Revving (2k RPM) the engine for 8 seconds brought it up to 14.1v during revving and 12.65 at idle, revving for another 10 seconds brought it up to 12.85

I'm going to assume that's perfectly okay

RicK G wrote:Doing it that way you will count the light coming back on in readiness for the next code and you get one more than it actually is. The normal state for the light is on.

StefanMajonez wrote:
I do count the light coming back on, but I strongly disagree I will count one more than there actually is. . . .So the most probable culprit is the battery (or voltage in general),. . .

By your calculation, there are 7 dips. According to information provided by the technician whose site is at the links I have posted, seven dips mean the  ABS hydro unit—not the battery—needs to be replaced with a working unit because the faulty unit cannot be repaired.

Laitch wrote:

RicK G wrote:Doing it that way you will count the light coming back on in readiness for the next code and you get one more than it actually is. The normal state for the light is on.

StefanMajonez wrote:
I do count the light coming back on, but I strongly disagree I will count one more than there actually is. . . .So the most probable culprit is the battery (or voltage in general),. . .

By your calculation, there are 7 dips. According to information provided by the technician whose site is at the links I have posted, those dips mean the  ABS hydro unit—not the battery—needs to be replaced with a working unit because the faulty unit cannot be repaired.

The 7 dips was an example I put of how I count them. As I said in the main post, I get either 6 or 7 randomly.

According to the information in your links, 6 is ABS relay and 7 is ABS brain. But both can be caused by the battery.

Looking at the voltages in my latest comment I'd say the battery is okay. So is it the brain? What should I do now?

StefanMajonez wrote:
Looking at the voltages in my latest comment I'd say the battery is okay. So is it the brain? What should I do now?

The way I interpret Tosi's information concerning ABSII faults, a defective ABSII pump unit can be replaced, according to his guidelines, but not repaired; a defective ECU can be repaired or replaced; a defective relay can be replaced. If codes 6 and 7 can also be interpreted as code 5, all I have to observe is I'm happy not to have ABSII on my moto.

StefanMajonez wrote:Looking at the voltages in my latest comment I'd say the battery is okay.

I agree. Unfortunately I know nothing about the ABS.

I guess I'll just observe exactly what's happening, gather some data, and read the websites Laitch provided. Maybe poke around with a multimeter and test some ABS connector pins.

Thanks for the help!

Laitch is correct about the vagueness of the fault codes.

My K100 gave me one initially, for the front pump, but then only gave me  seven flashes , no matter how many 

times I read the codes.

Two ABS brains later  and still seven flashes , I found a low resistance value from my front modulator

which cured the problem.

I could not understand why I did not get a consistent one flash code , which was correct, 

instead of the brain reverting to seven every time I tested it.  

I tested my codes with the two spare brains I bought, and never got a one code again, just seven....

Weird and not very helpful .

Months later, I  suffered from  a poor front brake light switch which made ABS light stay on, but the system has

been very reliable for a long time now, so stick with it..

For all the issues I had, I  prefer to ride with the ABS working.

Bob