!! For your safety !!
If your ABS is defective, disconnect the 25pin ABS connector until you get a repaired ECU or a properly working ECU otherwise you will be put in NO brake circumstance that cannot be predicted.
Milky way Technology Japan.

I will work on ABS1
as long as you can view
this page.

Don't work on iABS.

The contents on this page is only for ABS1, if your ABS type is ABS2 please click the link below for ABS2.
Go to ABS2 repair or reset info page

Please click this link to have successful error reset or to have final check before you send the ECU to me.

Home ABS1 Repair ABS2 Repair German French Itariano Brain for sale Feed back Modulator test.

Thank you for visiting.
This site will help to fix your problem with your BMW K Series ABS error .
I can repair your faulty ABS brain (ECU).

Contents on this page
1.Some History
2.How to read the error code
3.How to reset the ABS brain.
4.The ABS error code and meaning
5.Repair work example
6.Brief description of the inside of the ABS brain
7. 25 pin ABS connector pin assignment.
7A. How to disconnect the 25pin ABS connector.
8.Error code and defective components.
9.Correct diagnostic LED connection or you will get error 7.

1.Some History
In 2005 I purchased a 1990 K100 RS that had a fault with the ABS system which showed up as an error code 7 following a bit of research I tried to reset it but that did not work.

My research showed that for a long time after the BMW K series was released, many people had tried to repair ABS brain faults but had failed and it had been widely assumed that the brain was impossible to repair. Looking at the price of a new one I found they were prohibitively expensive so I opened up the ABS brain from my bike and as soon as I did so I thought, "I can fix this".

The reason for my confidence was that my background 20 years previously was in designing embedded systems very similar to the design of the ABS brain I was looking at and using similar vintage components. That gave me the confidence to start the long process of mapping the circuit diagram for the unit and then deducing the internal firmware coding which with the components of the unit make it work.

I spent most weekends for about 6 months working on the circuit finally completing a hardware circuit diagram, all by reverse-engineering the unit I had. During the course of my research I found that brain internal faults can be the true cause of error 1, 2, 3, 4, 5, 6 and 7 as well as faults external to the brain.

If you have replaced or adjusted the relevant parts based on the brain error code of your unit but that did not fix the fault then this site will be your last resort.

As a bit of background - the following are the required conditions in order to accomplish reliable repair work on any product like an ABS brain.
  1. A full circuit diagram of the product, other than the original manufacturer I believe I am the only person who has this. Doing repair work without having the circuit diagram for a piece of high-tech equipment like an ABS brain is very risky.
  2. A copy of the control program listing (some people call it firmware). Again other than the OEM I believe I am the only person who has this.
  3. A deep knowledge to hardware, software and circuit components from having worked on similar systems.
  4. Wide experience in digital circuit repair work
  5. Full tools like a logic analyser and a memory oscilloscope.
  6. Experience of how to control hardware using software
  7. Experience of the risks of Electro Static Discharge (ESD) to avoid hidden damage caused by ESD. The problem with ESD damage is that it often doesn't show up immediately
Having first done all the checking of the connections to the wheel sensors and the big plug on the ABS brain are clean and treated with DeoxIT then it is time to read the error code.

2. How to read the error code at the diagnostic connector located under the seat .
Locate the diagnostic connector under your seat.
Temporarily remove blue dummy plug if yours still has it.
Connect the positive lead of an analogue tester or DVM to the 2nd (middle) terminal hole.
*You can use only fast response DVM to read.

If you use the LED checker to read the error code, the LED circuit must be the resistance value of 8 kilo ohm or more in series or the circuit will overload the internal diagnostic logic and may produces error 7.

Connect the negative lead of the meter to battery negative or a good frame ground. The tester must be set to measure 15volt DC or higher.
You will see dips on the meter needle reading if the brain can show an error code as soon as you turn the ignition ON and it repeats showing the dips and steady 10 volt or so.
The number of dips indicates the error code.
If you can read the error code by doing the above I can almost certainly repair it. If you don't see any dips, then the diagnostic output related defect maybe exists and I can repair the case.

It is my pleasure if I can be of the help to BMW K rider whose ABS brain shows an error code .
Please read the software section explanation below to sort out if the internal brain is really defective.
External issues in the wiring or connections or modulator defects can cause error codes including seven.
3. How to reset the ABS brain
I have experienced many times that the ECU sent to me was not defective but just a failed error reset. Please follow my error reset steps explained on this link. especially follow the steps written in red letters.
If you let me repair your ABS brain, Please read the details of repair by clicking above "Repair detail" button or this link.

4. The ABS1 error code and its meaning.  
BMW says so but defective brain can cause any error.
Error code Meaning Auto reset on next ignition ON ?
1 No response from Front modulator No
2 No response from Rear modulator No
3 Open or short circuit between the brain and Front speed sensor No
4 Open or short circuit between the brain and Rear speed sensor or between pin 3 and 4 of 25 pin connector. No
5 Low battery voltage, needs battery charge or replace Yes
6 Defective ABS relay but weak battery can cause this error No
7 Internal brain defective but weak battery can cause this error No
8 Front and/or Rear Speed sensor gap incorrect Yes

The number of brains I have repaired is
Type of Brain units repaired so far those customers are from
Both(ABO1.5 and ABO2.5) many Spain,Japan,U.S.A.,Germany,Canada,Finland,Denmark, England,Hungary,Austria,Australia,France,Norway,Sweden,
New Zealand,,Romania,Swiss,Greece,Belgium ,Netherlands.etc.
None of them have been returned to me for re-work!

ABO 2.5 used in late K100, K100RS,K1100,K1, & 16 valve brick. ABO1.5 used in K75, early K100 8 valve brick.

5. Now I will show you an example of how I repair an ABS brain .
I am sure no other work shop can parallel or exceed my work because they don't have tools or the technical information that I have.
This sample brain was showing an error 7 after one sec. from power-on even after the error reset had been done.
The photo on the left shows a logic analyser trace from power(ignition) on and up to the point where error 7 occurred.

There are 15 check routines coded into the micro program and one of them found a reason to determine the problem as an error 7 state and output a diagnostic code of seven to the diagnostic plug pin #2.

Next picture logically continues to the right of this picture on left.
The notable point with the picture on the left is the 5th line from the bottom.
It begins at High level and keeps it for 0.3 sec. and then goes Low level for 0.3 sec. This is the internal signal of the diagnostic plug output and you will see an LED blink if you connect an LED check tool to this plug while in this state.

The repair work is done reading the info from the analyser trace and comparing it to the program listing and predicting the point and possible defective parts. Checks of those parts with a multimeter for simple parts or an analyser for complex parts will determine which are defective and which need replacement. As mentioned above there are 15 possibilities to be the source of error so repairing the first error allows the next error,if one exist, to show up.
To repair your ABS brain I repeat this until no more errors occur.
Furthermore, I have often found that if the repaired brain is powered on for 2 days then a new error will appear on the 2nd day. From experiencing these faults showing up after repair I have decided to include 48 hour continuous power-on soak test for all units I work on. this ensures more reliable repair work.

What I do after repair work other than described above is:-
1. Check error detection functions 1 thru 8 by simulating each fault that would cause the respective error code.
2. Check red ABS warning lamp blink on and off function.
3. Check bulb monitor triangle lamp blink and off function.
4. Check ABS relay drive power and on-off function.
5. Check front and rear ABS drive power and timing .
6. Check ABS cancel button function.
7. Check error memory writes , and the read and erase (reset) functions.
8. Road test for actual ABS activation function using my K100RS.
9. 48 hours continuous power-on test after repair work to check no more errors occur.
The repaired brain that clears all above checks is returned to the client.

6. Brief description of the inside of the ABS Brain
Stage one: Internal control software program flow.
Stage one begins
1. Hardware reset for 100ms after ignition ON. this resets the control CPU to initial state.
2. Initialize the CPU I/O ports before use.
3. Read the error memory and check if any error was recorded, if so skip to state ERROR DISPLAY.
4. Red ABS lamp starts to blink.
5. CPU internal RAM and ROM check.
6. Speed sensor bias control check, state generator function check.
7. Check analogue circuit response time by applying a test signal.
8. Check comparator function by applying a test signal.
9. ABS relay ON for one second, you should hear a brief sound like a mosquito flying from only the rear ABS modulator. It takes almost six seconds from step 1 up to this point; some people feel the sound as more like something moving inside the modulator .
Your ABS brain may have an internal defect if you cannot hear the sound .this is an important point.
During step 9 above, you will hear double click sound which comes from the ABS relay on and off.
If you hear the sound more than seven seconds after ignition ON that suggests your ABS brain has a minor problem and needs time to retry error checking.
10. If no error is found so far then the program waits for bike movement whilst still checking for any errors .
This is the end of stage one.

Stage two begins
11. If the bike moves it enables the red ABS lamp OFF, ABS relay ON, check modulator function & check sensor gap.
12. If ABS is activated it checks the timing to deactivate ABS & for check modulator pressure error.
13. Check for error 1,2,5,6,7 and 8 then repeat from step 12 above as long as ignition on and no error is found .
14. Check comparators, selectors, ABS activation drivers and modulator feedback by feeding test signal at intervals of 13 seconds .
Stage two end.

If your ABS brain generates error code seven and a reset sequence does not reset the error, to sort out what is defective proceed as below.
A. If you cannot hear the mosquito sound from the rear modulator after six to seven seconds from ignition on, then an internal brain defect is likely.
B. If you can hear a mosquito sound from the rear modulator after six to seven seconds from ignition on, check resistance of ABS connector pin #9(+) and ground(-), and pin #11(+) and ground(-), they must show approximately same value or the modulator is likely to be defective.
Also check the resistance of ABS connector pin #10(+) and ground(-), and then pin #12(+) and ground(-),. they must show same value or the modulator is likely to be defective.
The expected resistance value range is kilo ohm order on pin 9 and 11 & hundred kilo ohm order on pin 10 and 12 .
Caution: Measuring resistance is better than not doing so but is not the best because most of ABS related components are active devices that means measuring resistance does not always tells the true value. You need a logic analyzer and program listing to know exactly which is defective.

If your error code is one or two or both, I recommend you to perform the modulator active test as written here.

The program comes here when it find any error and never exits until the ignition is turned OFF.
What it does is as follows.
  1. Output error code to moditec out port. red ABS and bulbmon lamp blinks. The ABS is disabled.
  2. Record error value to error memory.
  3. Output error value in binary format (H level or L level) to diagnostic plug #2 pin .
    ex: when output error 2 , output H for 3 sec. then L for 0.3 sec. and H for 0.3 sec. and L for 0.3 sec. and H for 0.3 sec.
    Repeat this error sequence display until you reset the error or turn the ignition off. Low level is 0.5 volt or less ,High level is approx. 10 volt.
    What you need to count is number of low voltage dips you see on the volt meter in between 3 sec. H level portion, the count is equal to the error code .
  4. Switch ABS & bulb monitor lamp from blink to stay ON for 10 minutes if ABS cancel button is pushed.
  5. Clear error memory (reset function) if diagnostic plug #2 is zero volt (you need to connect plug#2 and frame ground) ,this is the primary condition, and ABS cancel button is pushed more than 8 seconds under the primary condition.
    The time required to reset error will increase up to 30 SEC. if the internal program finds any error.
    You must turn off ignition after reset performed so that reset becomes effective on next ignition ON.

7. 25 pin ABS connector pin assignment.
*The meaning of In/ Out is if the ABS brain receive the signal or supply it is In, and if the brain outputs signal it is Out.
The picture shows the connector pin numbering  you will notice that there are 13 pins on upper row where 12 pins on rower row. The wire bundle comes from the left side.
Pin# In/ Out Assigned for
1 In Front speed signal
2 In Front speed signal
3 In Rear speed signal. also detects short or open circuit between pin 3 and 4.
4 In Rear speed signal
5 In ABS cancel switch status
6 Out Front ABS activation
7 Out Rear ABS activation
8 Out Bulb monitor control (triangle lamp blink control)
9 In Front modulator status A
10 In Front modulator status B
11 In Rear modulator status A
12 In Rear modulator status B
13 --- Rear modulator ground
14 --- Negative(Ground) supply
15 In Positive supply(Battery +) for ABO 1.5  (For 6 or 8 valve engine only)
16 In Positive supply(Battery +) for ABO 2.5  (For 16 valve engine only)
17 Out ABS relay drive
18 Out ABS warning relay drive
19 --- Negative for relays
20 In For BMW tools
21 Out For BMW tools
22 No connection
23 InOut ABS diagnostic out and  error reset In.  You must leave this pin free of load  during normal riding.
 This pin is connected to the pin#2 of diagnostic  connector so you  must keep free of load on pin#2 of diagnostic connector  or you will not be able to reset the brain.
24 No connection
25 --- Front modulator ground

7A. How to disconnect the 25pin ABS connector.
I show you how to disconnect the big ABS connector from the ABS box.
Left side of the below photos shows when the connector is disconnected.
you will see the metal plate secured by 2 screws. it is the latch mechanism.
You need to push this plate toward right side to unlatch or disconnect the 25 pin connector.
Right side photo shows when the connector is connected. you need to push both end of the latch plate with your thumb and pointing finger while you pull up the wiring loom to disconnect the 25 pin connector.

8. The error code you got and the possible defective components
Error code Brain(ecu) Battery Front speed snsr *1 rear speed snsr
Front modulator
*1, *2
Rear modulator
*1, *2
Bad 25pin connector
1 y y y
2 y y y
3 y y y
4 y y y
5 y y y
6 y y y
7 y y y y y
 *1: includes wiring and under tank connector to it.
 *2: Perform  modulator test if the 5 pin connector located under tank cleaning does not help.

8a. The Error display LED circuit or diagnostic LED circuit I recommend is as following
<-------To Battery positive terminal (+) ------Anode of diode, Cathode of diode ---1 kilo ohm to 10 kilo ohm resistor------> To the diagnostic plug # 2 (center of three pin connector)

9. Correct diagnostic LED connection or you will get mysterious error 7.
There are a lot of wrong info about how to connect diagnostic LED to the diagnostic plug pin#2.
The wrong info says, connect LED anode (or plus) to diagnostic pin#2 and LED negative to ground, this is wrong.

Correct one is, LED anode (or plus) goes to Battery positive(+) and LED negative goes to diagnostic pin#2.
You need to put at least 1 kilo ohm resistor in series to protect LED.

The reason is that as I explain for pin#23 above, this pin has two functions. One is to monitor the voltage at this pin and the other is output the error code.
While the internal logic is checking the voltage of that pin for POST, this voltage must be more than 7 volt so that the logic determines the voltage is good. This pin can sink (in other word, pull) 100 mA current but can supply only 1 mA or so.

To give 7 or higher voltage at this pin you cannot connect any load that is lower than 13 KILO OHM . But if you use the connection I explain above you can leave the check circuit connected always. this one does not interrupt the normal operation.

Also the LED of this connection does not illuminate while the ABS has no error and shows only the number of error code.


inserted by FC2 system