ABS light turns on during driving

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Inferno
Joined: Sun 30 Sep, 2012 07:35
Posts: 277

  Z3 roadster 1.8
Location: Athens

ABS light turns on during driving

Post by Inferno »

Hi,
I have this issue i used to have it again about 7-8 years ago and again 2-3 years ago, so i will try to take the story from the top.

About 7-8 years ago i started having an issue with the ABS light coming on and staying on. I visited my garage shop and in the process of troubleshooting the problem we changed a front wheel sensor which didn't fix the problem and then we replaced the ABS main unit with a used one which finally fixed it.

Fast forward 2-3 years ago i started again to have the same issue, only this time the ABS light was going away everytime i turned off an on engine, i visited again the garage shop, car stayed in for several days as they were trying to idenify the problem which was persisting. They even replaced again the ABS unit which still didn't helped, finally after 100 of fault code resets the problem went away. Then i had 0 issues until lately when the problem started happening again only this time is a bit different and quite dangerous as it feels like i have no brakes. As i am driving with the ABS light off, i suddenly feel the brake pedal vibrating like when ABS comes on, i can hear an electrical sound (again like when ABS comes on) pedal goes weak and deep and then ABS light comes on and stays on until i turn off and on engine. It basically reacts exactly like when you brake on ice.

Any ideas? I really don't know how this will be fixed if it comes down to be a wiring issue...
LaRy
Joined: Mon 12 Nov, 2018 17:47
Posts: 154

  Z3 roadster 2.8

Re: ABS light turns on during driving

Post by LaRy »

Hi, I had ABS problems some years ago and spend lot of time trying to fix it, and solved it. I was reading everything, and I know that BMW is sending the ABS boxes to Netherlands to a company fixing and repairing, but in your case I would send the first unit placed in the car, by reasons I will explain later. I also got fault code like front wheel sensor broken, but noticed that the fault code settings aren not as accurate as today, the change did not work.
I don't know how deep in technical level you want to go, but if you want to dig all the way to the bottom, come back!
Number one, what I read and can also comfirm, to replace by a used similar ABS box does not work. It only works, if you have a BMW special tool, making it possible to clone the software from the old one to the newer used one. The software is exactly made for your car and the specification like engine, gearboxm equipment...Most of the BMW workshops do not have that equipment any longer.

But I will now tell you how it ABS works, and it will help you to understand. Everytime you turn on the ignition, a self ckecking program will start in order to check all connected equipment. When the feedback from checking is OK, the ABS relay will be activated. You notice that by turning the ignition on, and of you listen carefully, you will hear a click from the ABS relay, and at the same time the indicating lamp will be off, even if you not start the engine. That relay, assembled together with the other relays was broken in my case. That was my actual fault. No click, but electricity to the relay coil. Normal checking time, 2 seconds.

Anyway, the self control is mostly checking the abs sensors in the wheels, the valves in the ABS pump unit, and the coils in the ABS pump unit. It is wellknown that the electric connentions and the coils in the ABS pump unit are poor. How is this checked? By unplugging the ABS electronic and check the reistans of every coil and sensor, totally 9. THe value must be within a certain window. Same for the ABS sensors in the wheels. If value is outside the value window, the ABS relay will not be activated.
If you are prepared to check all those values, please come back!

It can also be the ABS pump relay.

I would say that according to what I have been reading, it is 50 % chance that the ABS pump unit is causing your problem. You can try to get a new unit, and see if it works. Some people open the unit and start resolder the valve coils. To disassemble the ABS pump unit means also disconnection to all brake tubes connected to it and afterwards breath the system. To me, it sounds more like a ABS pump unit problem in your case, as you have that vibrating feeling in the brake pedal.
So, please come back if you want to dig into the deeper level meassauring values from the plug, with approximately 24 pins.
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Inferno
Joined: Sun 30 Sep, 2012 07:35
Posts: 277

  Z3 roadster 1.8
Location: Athens

Re: ABS light turns on during driving

Post by Inferno »

Thank you for your detailed reply. I found an ABS repair shop in UK, if the problem is the ABS unit (i haven't visited my garage yet) i will send it there. Do you know if the car can move without the ABS main unit or it has to stay in my mechanic's shop for all those days?
LaRy
Joined: Mon 12 Nov, 2018 17:47
Posts: 154

  Z3 roadster 2.8

Re: ABS light turns on during driving

Post by LaRy »

The Z3 has some different solutions. In some cases, like in my car, the ABS electronics is placed behand the glove compartment. In some other Z3's in can be placed together with what I call the ABS Pump Unit.
My guess is that the car can be used even if you remove the ABS electronics behind the glove compartment, but to renovate and check the ABS pump unit it must be removed, as I see it. The unit has aproximately 8 brake fluid tubes connected, so it must be there for driving. It can not be used. But it is good that you are using a local garage to take the unit out. Not much space and the system will need a professional bleeding when the unit is back.
I looked at some Youtube movies, and for me, it is looking more like a ABS pump unit problem. Have a look at https://www.zroadster.net/forum/viewtopic.php?t=45565e .
This is the best solution and can probably be driven without unit.
Mine is looking like this, and must probably be totally disconnected when repaired. https://www.youtube.com/watch?v=JZcWXSX9aQs
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Inferno
Joined: Sun 30 Sep, 2012 07:35
Posts: 277

  Z3 roadster 1.8
Location: Athens

Re: ABS light turns on during driving

Post by Inferno »

Yeah mine is like the first one, inside the engine bay
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