!! 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.
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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
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.
8.Error code and defective components.
9.Correct diagnostic LED connection or you will get error 7.
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.
2. How to read the error code at the diagnostic connector located under the seat .
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.
The number of brains I have repaired is
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.
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.
state ERROR DISPLAY:
The program comes here when it find any error and never exits until the ignition is turned OFF.
What it does is as follows.
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.
8. The error code you got and the possible defective components
*2: Perform modulator test if the 5 pin connector 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.