ABS Light is ON -How do I isolate which sensor is defective

I am asking for some help with this.
I have a 92 roadmaster wagon with 197,000 on it. The ABS light just came on. How do I isolate which sensor is defective?
I can disconnect each sensor and I believe I can put a meter on the terminals. Any idea what I should be reading?
A general question is - How to troubleshoot the ABS system in any car?
Thanks for any help
Dan
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Greetings,
Well I guess the first question that needs to be asked is how do you know it's a bad sensor? Even in a vehicle from '92 it could still be a bad circuit/wire, control module, ABS pump, etc. I guess what I'm trying to say is instead of concentrating on just the wheel sensors you should just go have the computer scanned to see what it really is or may be, and if it turns out to be a bad sensor then it may tell you exactly which one instead of trying to find it yourself.
Good luck - Jonathan

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He can do this one himself. Short pins 'H' and 'A' on the ALDL connector, turn ignition on. ABS light will flash codes.
Remember: 1. Read codes. 2. Reset. 3. Test Drive. 4. Read Codes.
Report back with your findings.
Steve
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I gather this approach only works on OBD-I vehicles ...?
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Yes, but not all.
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Well, I really want to thank you guys for showing me where to start my diagostics.
I have finally had the time to do some research on my ABS problem.
The ABS light is now always on instead of being intermittent.
The error code is 25, which I have found on the web as being "Left Front Speed Sensor Fault".
My intensions are to clean the connector contacts and clean the sensor area to remove any dirt which my interrupt the magnetic flux. I will most likely do a resistance check on the sensor since I will have it disconnected.
Anyone have other suggestions?
Thanks Again -- Dan

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Give it a try Dan, but don't be surprised if it does not work. You've got maybe a 50/50 chance. You may find you have to replace the hub assembly because the sensor is inside the hub.
Before jumping on the hub though, check the integrity of the wire from the connector down on the A frame, up into the engine compartment. I don't know where it runs to on your car - you'll have to trace it or research its routing. It's not completely uncommon for the wire to corrode and fail.
--

-Mike-
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On this particular vehicle, the front wheel bearings are not the sealed unit type. The ABS wheel speed sensor is independent of the wheel bearings.
Still check all the wiring, but check the continuity of the sensor itself first. It's a quick and easy task that could save you a lot of time troubleshooting wiring that's not at fault.
Steve
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Good stuff Steve. Thanks for pointing that out.
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