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ABS Issue/Anti-Lock Light

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  • ghrays
    replied
    I had a similar issue with intermittent flashing of the ABS dash light. Turned out to be due to a faulty connection at C101 (pin 20).

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  • hopeful
    replied
    There has to be some form of diagnostic process to this aside from what's above? I can't imagine this is what dealer Tech's we're doing when the abs light came on. Maybe some older generic abs scanner would work?

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  • zaq123
    replied
    Originally posted by VitalkaE30 View Post
    Bump. Was this ever solved? Currently chasing the same issue
    Originally posted by E30Bastard View Post

    Unplugged all the sensors and did spin test - Both front sensors set the light off and both new rear sensors do not.

    It's kind of hard to follow OP's posts in this and his other linked thread about CV axle issues. If all sensors are unplugged, how can front sensors set the light off?


    In any event, here is some useful info from the man - the legend himself


    Originally posted by thejlevie

    ABS Diagnostics
    The ABS system on an E30 is pretty simple. It consists of a wheel speed sensor at each wheel, and ABS module & relay above the steering column, and the ABS unit in the engine bay. It has no connections to any other parts of the car.

    If the ABS light comes on when the ignition is turned on and doesn’t go off when the engine starts the relay, module and unit are all suspect. There is a fusible link in the ABS relay that, if blown, will cause this. The fuse (a simple piece of wire) can be replaced, or better yet get a new relay. If that fails to solve the problem the ABS module or the ABS unit are the next suspects. The ABS unit contains relays that have been known to fail and can be replaced with OE parts. So you have two choices. replace the ABS module with a known good unit, or replace the relays or the entire ABS unit. I start with the ABS module.

    If the light comes on with ignition, goes out with engine start, and comes back on once the car starts moving, one (or more) of the wheel speed sensors is bad or the ABS module is bad. A simple test of the speed sensors is to disconnect all but one and see if the light comes on while driving. Since the ABS system only gets speed data from the wheel speed sensors, a good sensor will cause the light to come on as the module doesn’t see data from the other sensors. Repeat this test with each of the other speed sensors. A bad one will cause the light not to come back on as the ABS module can’t tell that the car is moving. Replace that sensor(s) and see what happens. It is possible that one or more of the input channels in the ABS module are bad.
    ​​​

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  • VitalkaE30
    replied
    Bump. Was this ever solved? Currently chasing the same issue

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  • moatilliatta
    replied
    Id try the old axles again.

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  • E30Bastard
    replied
    The inside of my hub...just in case...idk... Sent from my Pixel 2 XL using Tapatalk

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  • E30Bastard
    replied
    Originally posted by dasmanschaft012 View Post
    silly check, make sure a) theres high resistance between the sensor wires and chassis (maybe somewhere in the body the harness rubbed thru) and b) check resistances between each sensor wire with the control module unplugged to make sure the sensor wires aren't shorted together or pinched somewhere in the cable run.
    Here are the resistance results:
    Passenger side pin 1 to abs module - 0 resistance
    Passenger side pin 2 to abs module pin - 0 resistance
    Driver side pin 1 to abs module - 0 resistance
    Driver side pin 2 to abs module - 0 resistance


    These wires run from underneath the rear seat directly to the ABS module. They test perfectly and have been ruled out.



    Driver side sensor resistance - 1.04k
    Passenger side sensor resistance - 1.023k


    These are the two sensor wires that run from the connectors underneath the rear seat through the firewall and to the rear hubs. These brand new sensor wires have been inspected multiple times and tested multiple times. They are good.



    Rear driver circuit resistance tested from abs module connectors/pins: 1.04k
    Rear passenger circuit resistance tested from abs module connectors/pins: 1.023k


    This is testing the entire circuit at the ABS module itself, getting the same reading as I did from the sensors alone again means the wires running to the ABS module are perfect.






    Some notes/observations:

    I can make the light trigger with either of the rear sensors plugged in if i make a slow uturn or i go in reverse and toy with the clutch so as to make the rear end hump or stutter. The wires are 100% good, so what physical issue with the axles or diff would cause this? I just replaced a GKN axle with a chinese axle just to try something else to see if that would make the light come on and I have the same behavior.

    It is now pouring rain and I could really use ABS. I've pretty much exhausted everything I can test on this simple, standalone system.

    Any suggestions aside from electrical problems (which I have determined through 5 different ABS modules, 4 new rear sensors, and extensive electrical testing to not be the case)?

    Much appreciated!!!

    P.S. Edit - Just to reiterate - if I plug in either of the front sensors, the light triggers as soon as I start rolling forward. Expected and correct behavior per the Jlevie spin test. The pump and the computer are getting voltage. And just for good measure all relays at the pump and underneath the dash have been replaced with new relays.
    Last edited by E30Bastard; 12-07-2019, 12:54 PM.

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  • 2mAn
    replied
    https://s14net.vbulletin.net/forum/s...ights-si-board

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  • moatilliatta
    replied
    Did you back probe the ABS pump and computer for 12v and ground?

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  • dasmanschaft012
    replied
    silly check, make sure a) theres high resistance between the sensor wires and chassis (maybe somewhere in the body the harness rubbed thru) and b) check resistances between each sensor wire with the control module unplugged to make sure the sensor wires aren't shorted together or pinched somewhere in the cable run.

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  • 2mAn
    replied
    Why ABS .... WHYYYYYY

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  • E30Bastard
    replied
    Hmm, I have 4 new sensors...same behavior with all. I was thinking about jacking up the car and putting it in first to see what the sensor puts out when wheels spin... Sent from my Pixel 2 XL using Tapatalk

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  • moatilliatta
    replied
    Maybe right click and save as or open in new tab, maybe its getting blocked.

    New parts can be bad.

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  • E30Bastard
    replied
    Your link doesn't work. The sensors and wires have been checked. It is definitely something other than the brand new axles, brand new sensors, and verified rear circuits. Sent from my Pixel 2 XL using Tapatalk

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  • moatilliatta
    replied
    Looks like it is a closed system...

    1988 model year 325 page 42 - Id just check all the inputs and outputs after going backwards on what you installed. IE rear sensors and axles.

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