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Discussion Starter #1
Hi all,

I'm new to the forums, but have seen some great trouble-shooting tips here, so hoping I can get some tips here related to my Z3.

I have a 2001 2.5i with a brake issue. I've had it for a while but finally got around to trying to actually fix it. Initially I could drive down the road and at some random point the brakes would grab, let go, grab again and then after a couple of times the ABS, Brake, and DSC (triangle with the counter clockwise circle/arrow) lights would come on. After that the ride was fine, brakes worked, no apparent issue other than the lights and likelihood that the ABS wasn't functional at that point. As time progressed the car would randomly start up in this mode. IF is started it and remembered to press the DSC button to de-active it before driving, then no issues ever. The speedometer and odometer have worked fine in all these scenarios.

Reading the posts, the likely candidate was a bad wheel sensor, and since the speedometer and odometer were working, it seemed like one of the front sensors were bad. So I finally jacked up the whole car, removed all 4 wheels, and checked the sensor resistance. Using the diode setting on the multi-meter I get an OL (open) in 1 direction but then 20-22 Mohm in the other (that's right MEG-ohm). All 4 of them are the same. From reading posts this is way too high, but it seems unlikely that a 4 are bad. I did test a M3 sensor for comparison it was like 1000x lower... to testing technique is OK I think.

There seems to be a great post from BlueBee in 2009 related to an E39, but not sure how applicable it is to the 2001 Z3. Any suggestions or pointers to more applicable Z3 threads would be appreciated (searched but didn't seem to come across any).
 

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Discussion Starter #3
Thanks. I did take the Z3 to my regular shop, and their BMW auto repair scanner was unable to read anything related to the ABS/brakes. I thought I had read elsewhere that this particular model year didn't have info on the ABS/DSC function/status. But its easy enough to try, so thanks... Will keep everyone posted.
 

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Also, you cannot access the ABS/DSC from the OBD connector in the passenger compartment. You need to connect to the computer port in the engine compartment.
 

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Discussion Starter #5
Update on ABS-DSC issue & testing

Hi all. So I ended up getting the NT530, and must say I like it so far. I've purchased two previous BMW specific scanners that weren't helpful, but this one (via the 20 pin connector) seems to have immediately pointed me in the right direction. The Laptop in the garage, balanced on a seat or something, just didn't seem like the trouble-shooting setup I wanted... so the NT530 is compact and so far good.

OK, to the issue I was trying to solve, DSC/ABS/Brake light on, most of the time from the moment I start up the car. The NT530 indicates the following ABS-DSC related faults:

5D90: Wheel speed sensor front left
5DA0: Wheel speed sensor front right
5DB0: Wheel speed sensor rear left
5E38: Rotation rate sensor
5E3C: Rotation rate sensor

1) First off, this sounds like the sensors in all 4 wheels are bad, yes ?
2) From what I had read one of the sensors had to be operational in order for the speedometer to work... is that incorrect then ?
3) And how likely is it that all 4 sensor are bad anyway, is this possibly indicating the master ABS ECU is bad ?

Ok, so what is the different between a wheel sensor and rotation rate sensor, seems like the same thing. And I'm assuming the last two codes are really right rear indicators anyway.

Basically looking for more clarity into what the codes themselves mean. I search the WEB and the forums here, but must not be using the right codes words.

I had mentioned originally that measuring the forward and reverse bias impedance indicated every sensor was like 20 Mohm, so if they are all 4 bad that at least would be consistent, just seems very unlikely.

Any pointing in the right direction would be greatly appreciated. My baby hasn't given any problems since I acquired her 2004, so I'm charting new waters here for BMW DIY repair.

Joe
 

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The rotation rate sensor is mounted under the driver seat and measures the rate in which your car rotates as in spinning in circles on ice. They seldom fail unless there has been water in the car. To get to it you need to remove the seat and pull the carpet back. It seems odd that all four wheel sensors would fail at the same time. I know that when these rate sensors fail they can throw unrelated codes so this may be your problem, its hard to tell. I would replace the rotation sensor first, clear the codes, then see what else pops up.
 

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Also, the speedometer sensor is mounted in the transmission and is unrelated to the wheel sensors.
 
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