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-   -   ABS sensor test with meter? (http://www.focusfanatics.com/forum/showthread.php?t=213388)

boatingfool 10-09-2009 08:01 PM

ABS sensor test with meter?
 
My Haynes manual states I can check my ABS sensors with a volt meter by connecting the meter, reading VAC and spinning the wheel. Either this is bogus or I have 4 bad sensor/wheel bearings.

I recently replaced all 4 wheel bearings and I have the ABS light. See other post.

http://www.focusfanatics.com/forum/showthread.php?t=212910

Thanks for any info

Vincent

roosterst 10-09-2009 08:27 PM

How fast are you spinning the wheel? Was the ABS light on before replacing the bearings?

boatingfool 10-09-2009 08:39 PM

I don't know the exact speed I was spinning, but it was by hand and pretty fast. The meter didn't budge. I tried the left front which is a new bearing (black ring inboard towards sensor) and on the right rear wheel which the bearing and hub was purchased preassembled from Ford (Trousley). Spinning by hand with the wheel installed as fast as I can and the meter didn't change.

If I read for ohms across the sensor, I only get a reading if I put the probes on a particular way, almost like it is a diode.

The ABS light wasn't on before I started the project. I removed/inspected all 4 sensors, installed, no visual damage. I checked all 4 connectors, connected.
I drove the vehicle after replacement. I tried disconnecting the battery before, but it didn't didn't reset. I tried again tonight, but nothing.

Vincent

jarchie 10-09-2009 08:46 PM

Send me your OHM readings. Do you have traction control? They use a different kind of sensor that will not produce voltage readings. pm me and I will try to help.

roosterst 10-09-2009 08:46 PM

Can you measure how big the gap is between the tone rings, and the sensors?

jarchie 10-09-2009 08:49 PM

By the way, on parts like these, i always go OEM.

boatingfool 10-09-2009 09:18 PM

The car does not have traction control.

The front wheel sensors read 3.625mohms/3.680mohms. I don't remember what the rears were and I just cleaned up for the night (frustrated) [rant].

I will check the rears tomorrow.

Again, I am only able to ohm the sensor if I have the test leads oriented one direction. If you reverse the leads, it reads open.

Thanks for the help.

Vincent

Oh, the front bearings were CFM but Ford OEM. The 2nd set of front I have to install were purchased from Trousley and are the same exact ones. I checked the black ring and it has a slight magnetic field. I removed the driver's side sensor and placed a ferrous tool (Snap on pick) and the wheel sensor ring pulls at the pick.

drjkel 10-10-2009 09:11 AM

Hall-effect sensors can't be tested the same way the older-technology tone-ring (relucator) and coil systems can be tested with a volt meter. I get zero volts on my voltmeter from all four of my ZTS's sensors while spinning the wheels (fast) (w ABS & traction) and both systems work fine.

penguin 10-10-2009 03:18 PM

Well, it also depends on the sensitivity of your meter. What AC range is it set to?

And, as someone said, if it is a hall effect sensor, rather than an inductive pickup type, the AC voltmeter test probably will not work.

I don't know which type the Focus uses, hall effect or inductive coil.

jarchie 10-10-2009 09:16 PM

At Ford, we refer to them as Active and Passive. Passive sensors are tested with an OHM meter and can be tested to see if they produce AC voltave (in milivolts) and Active require a 12V power source and are tested in AMPS. Your meter has to be wired in series with the negitive lead from the sensor to the module and the positive wire has to be complete with the key on. The signal should toggle from 7mA to 14mA. If you are in Charlotte NC week after next, I am teaching Advanced Brakes.


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