ABS lights - frustration!

UK forum for general and technical discussion about the Z3 roadster

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Joined: Mon 12 Nov, 2018 17:47
Posts: 21

  Z3 roadster 2.8

Re: ABS lights - frustration!

Post by LaRy » Fri 16 Nov, 2018 10:23

A couple of years ago, I also had this problem with the ABS light coming on after bringing the car out in spring time. I decided to understand how the system is working instead of reading fault codes. I was reading everything I could find in the internet. You know, this system is used in a lot of cars brands, and the program is making it to work in your car. Remember that car electronics and fault codes were in the beginning when these cars were made. For that reason the fault codes are often false, like in my case. My fault code= left front wheel sensor broken. I changed it and it did not help.
An experienced BMW repairman asked me if I really tested the function of the sensor. Later I did, and it was ok. Actually I tested all sensors.
In my case, the ABS light came on a couple of seconds after I put the ignition on. After my studies of how the unit is working, I know that the ABS unit is making a lot of self testing just after ignition is on, checking that the values of all connected sensors and valves are within specified (programmed) limits. The ABS unit was actually also connecting 12 VDC to the coil o the ABS relay K10, but the self test noticed that the contact in the relay became not closed. = ABS Light ON

In my case, it was actually the electro mechanical ABS relay K10 that was broken. So if the ABS light is coming on within a couple of seconds, open the hood and fuse box, listen for the click from the ABS relay. If it is broken, the light will come on instead. These cars are now 20 years old, and it is rather common that the relays can get broken.

How did I test the sensors: Disconnect an check the Ohm-value. If I remember right, it should be appr. 1 kOhm, at least same for all sensors. Second step: Put the multimeter to Volt AC, rotate the wheel as fast as you can by hand (wheel in the air of course). Voltage, maybe 1 - 1.5 V. Rather equal for all wheels.

Joined: Fri 30 Nov, 2018 23:20
Posts: 4

  Z3 roadster 3.0i

Re: ABS lights - frustration!

Post by zemoal45 » Wed 12 Dec, 2018 13:27

BladeRunner919 wrote:
Thu 04 Oct, 2012 08:30
I have this cable that i found on google:


which is a proper serial cable. Where in Surrey are you Dom?
it seems interessing but the link is dead, is there any alternative serial cable ?

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