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Thread: Testing for ASC ABS lights on continuously

  1. #1
    Join Date
    Jun 2007
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    Northern VA
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    718
    My Cars
    97 M3/4/5; 04 M3 6M

    Testing for ASC ABS lights always on

    This is for diagnosing when both the ASC and ABS lights come on when you turn the key and is, for now, limited to checking for a bad sensor. This is a test under the condition that both lights come on as a result of the self-diagnosis the car does every time you turn the key to ON, thus they are always on. If your lights only come on after driving a bit, it is almost certainly your brake pedal position sensor. I'm sorry this is limited to only three functions.

    What you see below is the test I did at the control unit connector behind the glove box. It is not the full suite because this is the only data I recorded and I found my problem pretty quickly (the problem is the on the right front—bad sensor replaced and now all is well). I am posting this because the posts I've seen had reference voltages and resistances that were not even close to what I found in real life, even in the ABS Teves MK IV guide (search for abs_teves4eng.pdf). I have no idea why that is, but here are my actual values for what I recorded. As it turned out, for what you see below, the relevant values are within the reference rage in the Teves guide.

    I tested a lot of other stuff and found values that were way off, which is why I said what I did about the reference values being unreliable. I even used a very thorough post with instructions that were two full pages long in Word at 10 pt. font size (so it has to be right, right?). As an example, it had me testing certain connections for 12 V. It said if I could only get 12 V for those connections by removing the ABS relay, then the relay was bad. I only saw 12 V with the relay removed. So I tested the relay, and as far as I could tell it did exactly what it was supposed to, but I bought a new one anyway. Waste of money. "Thorough" 2-page instructions were wrong!

    Also, the only required testing for the functions I tested is for their resistances and, for each of them, with the key in the OFF position (i.e., the only relevant readings are in column "Ω (off)"). All the other info I tested for was because I wanted to know.

    Note the pinouts are specific to the model/year, so you need to look them up in in the Electrical Troubleshooting Manual (or the Bentley) for your car. Go here to find the ETM for your car: http://wedophones.com/Manuals/BMW/. The ETMs only exist through the 2001 model year and the titles displayed may not be complete (mine did not include "M3" in the title...ha!). The info is much clearer than in the Bentley. These are the three pertinent pages for what I needed — all 55 pinouts, but only the wheel sensor schematic.

    M3 ABS-ASC CU Pinout pg 1 of 2.JPGM3 ABS-ASC CU Pinout pg 2 of 2.JPGM3 ABS-ASC Wheel Sensor Schematic.JPG

    Note: The ground connection I used for my tests, other than the ABS Speed Sensor, was pin 1.


    Function (1997 M3) Pin V (off) V (acc) Ω (off) Ω (acc)
    LEFT FRONT
    Solenoid Valve Inlet 17 - 9.1 m 7.3 15
    Solenoid Valve Outlet 54 - 9.1 m 3.5 11
    ABS Speed Sensor (G + V) 30 + 48 1.1 K 1.1 K
    RIGHT FRONT
    Solenoid Valve Inlet 22 - 9.1 m 7.3 15
    Solenoid Valve Outlet 37 - 9.1 m 3.5 11
    ABS Speed Sensor (G + V) 11 + 47
    LEFT REAR
    Solenoid Valve Inlet 17 - 9.1 m 7.3 15
    Solenoid Valve Outlet 18 - 9.1 m 3.5 11
    ABS Speed Sensor (G + V) 29 + 46 1.1 K 1.1 K
    RIGHT REAR
    Solenoid Valve Inlet 39 - 9.1 m 7.3 15
    Solenoid Valve Outlet 55 - 9.1 m 3.5 11
    ABS Speed Sensor (G + V) 10 + 45 1.1 K 1.1 K
    Last edited by HighandFast; 06-27-2018 at 06:44 PM.

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