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2001 Taurus Wagon-ABS activation when not needed. Always activates when stopping, when almost stopped. Replaced all sensors, calipers, ABS-control module. No ABS DTC. Occasional ABS light when driving, not braking. Scrubbed all 4 rings with wire brush to remove rust buildup. Oscilloscope shows normal sensor function. I've printed off all the diagnostic tests from Alldata, but have not done them yet since none are indicated by my symptoms. I'm removing dash now to do tests from Alldata.
When I cleaned the tone rings with a wire brush, I also cleaned the sensor mounts. If you know the spacing, I can check the spacing between the tone ring spoke and the sensor, front and rear, but especially the rear since they protrude more. I'm following the Alldata "pinpoint test" for "ABS light on" with "no DTC set" since this problem is the closest to mine.
Yes, I cleaned the mounting surfaces where the sensors bolt on, each of them... The front end was aligned last month, there is no bearing type noise or vibration. Also no noticeable play in the front end, when I checked the tie rod ends and ball joints. It tracks straight at acceleration and cruise. (Just trying to think of what else might tell if a bearing is bad... all the ones I've changed have either shown wear in being loose or by making noise). I did read that bad bearing could cause problems so I did try to feel for any looseness in the wheels. Car has 75k miles, but that hasn't stopped it from having a load of issues!
That's why I replaced the ABS control module... Only thing left is the ECU or the wiring harness. Right?
The dash wire test I just did said to measure the resistance between pin 25 on the ABS module side harness to the dash pin 1 connector (both Green). It says to replace the "Electronic Control Unit" if the resistance is less than 5 ohms. I was following the circuit diagram and you are right that the ABS controller does not interface with the Engine Control Module. Using my standard electronics meter, set at Ohms, 20k, there was 0 ohms resistance. Set at 200 there was point 7 ohms (.7) resistance. Yes the ABS control unit is used. Yes I did match the numbers since this Taurus does not have Traction Control. Sounds like I may have to spring for the expensive (new) ABS controller? Don't want to do that if I'm not certain it will fix the problem.
I'm use to ECU being Engine control also.
I just checked the pins and don't see any pushed back, am going to double check with the wiring diagram. The only other thing I wasn't sure about was the sensor rings, maybe needing to use a mini grinder to grind out the valleys since it was a northern car and there is still some buildup. But those don't look like they are replaceable(?). Thanks for the help, reassurance, and advice.
I meant the tone rings... they're not replaceable, or are they? I see Advance Auto carries them.