I have replaced both front sensors with genuine BMW units to no avail.
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The rear pulse wheels are pretty shot so I have the rear sensors unplugged to take them out of the equation. I plan on purchasing a new set of rings from http://www.reluctorrings.com/cars/bmw shortly.
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Anywho the front pulse wheels are in good shape and the sensors are brand spankin new. The connectors on the body side have crumbled a bit but they make fine electrical contact.
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My next suspicion was the ABS unit. I purchased one from a fellow member here and it purportedly came off a car with working ABS.....and it still didn't solve the problem.
I know in my E30 as soon as you roll away it does a quick little self test once you start driving and you can feel/hear the ABS pump. So the ABS pump was my next target.
First thing I did was test the relays. There was continuity between terminals 30 and 87a on the valve relay and once 12v was applied to terminals 86 and 85 the relay clicked and terminal 30 disconnected from 87a and connected to 87. Valve relay checks out. Did the same test for the pump relay and it checked out fine. Checked to see if power was getting to the relays. Power was getting to terminals 86 and 30 for the pump relay. That's odd, it should be 86 and 87 according to the ETM. I checked continuity between the abs harness plug prongs and the female relay socket connections. For the pump relay 30 was continuous with 13, 87 with 10, and 86 with 11. According to the ETM it should be 30 with 10 and 13 with 87. There is no continuity between 13 and 87 so I think this is just labeling boo boo in the ETM. I checked a spare ABS pump and it was the same way. I jumped terminals 87 and 30 with a short length of wire and the pump buzzed to life....so that works.
Back to the valves. Resistance of the valves was tested by probing connector 30 of the relay socket and terminals 2, 4, 6, 8 of the ABS harness plug prongs, Each read 2 ohms. Valves were tested by applying power to terminal 30 the of valve relay socket and selectively grounding terminals 2, 4, 6, 8 of the ABS harness plug prongs. All 4 clicked. Everything seems ok with the valves. The pump itself seems fine.
I then continued to test continuity of the wiring between the pump and the ABS module connector...all 8 wires checked out.
Next thing I checked was if the ABS module was getting power, pin 1 had 13.4V and pin 15 had 14V (1.6V before starting car). Odd that there is a 0.6V discrepancy but they're getting power. Pin 25, the brake input, gets 12.6V with the brake applied, none with no application. Checked continuity of pins 10, 20, 34 (grounding pins) with some metal part of the dash support. All three read 0 ohms demonstrating a good ground for all. Other than some minor voltage discrepancies, the ABS module plug seems to be getting all the correct grounds/power/signals etc.
So I unplugged the front driver's sensor so we're only playing with the front right sensor. Tested the resistance between module connector and the connector for the front right abs sensor, 0.2 ohms for both leads, pretty low. Tested the resistance of the sensor itself 19.9 kiloohms or 19900 ohms. I couldn't find a spec for e28 sensors but I have heard e30 sensors are 1-2K ohms. I know that e30s have different pulse wheels and such and is a different design however. So that curious. I should test the other sensor as well.
I filled in the ETM with my findings and realized I missed to test a couple things (like continuity between 86 and 12 for the motor relay) but it seems like everything is in working order and maybe I have another bum ABS module. Anyone have any input?
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