speed sensor failure cause

Only real test Is to check for resistance and compare with a known good sensor...hope it's not a 1998...there not available new....best bet is trying to find used if a 98
 
Thanks. i know the story on the 98's. I have a bad one and am just curious why they fail and how they are constructed.
 
My understabding is they have a magnetic contact to read the sensor wheels. That part moves. As time goes on it will stop moving like anything in gravity that moves. Warped plastic housing can do it, dirty contacts, contamination from other chemicals.....
 
Correct me if I'm wrong but I believe there is no magnets involved
It is electrical when it passes a tooth it is grounded and not grounded when there's no tooth. Then thereis a signal sent back to the computer from the sensor telling it complete circuit or not.
By the way the rear rings on a mark are aluminium. That's non ferrous but conductive.
 
Then my understanding is wrong.

Also they do not contact the ring so they cant ground to it. I figured it was a reading of magnetic field like the cam and crank sensors are.
 
I used to think it used magnets too but it didn't make seem right with the aluminium rings
 
beerdog said:
This was informative

http://www.brakeandfrontend.com/Article/46336/diagnosing_wheel_speed_sensors.aspx

http://www.discountautomotiveonline.com/2002465.html
Click to expand...
Well I was about to berate you again but half way through it does explain that they are magnetic. Its not a moving magnet but a wire wrapped around it like a coil and it reading the variance in magnetic field.

Soooooo, the rings have to be made out of something other than aluminum.


I guess failure would be attributed to a broken wire/coil or something demagnetizing the sensor.
 
They are aluminium but it could probably still see a difference of magnetic field cause
The ring would be more like an insulator regulating what the sensor sees of the half shaft
 
The bad sensors I have trigger the ABS light and turn of the traction control immediatly after being connected. I tried ohming known good and bad sensors. i checked 3 good sensors and I get an Open reading in one direction and 3MegaOhm in the other. On the known bad ones te Open readin in both direcions. According to what I read they are all bad due ot the high Mega ohm reading or these are not the type that can be ohmed out. At least it talks about getting an Ohm reading between 50-2000ohms. I think I saw another post that stated the reading should be 35ohms or so. Maybe this is one way the 98's are different.
 
Her eis what i am dealing with.

I had a ABS sensor for my 98 go bad. I got a replacement and it failed a week later. I also think I had a bad battery negative cable which I just replaced. Do you think a bad battery ground could have been causing some funky voltages to hit the sensor? Anyone else ever experience multiple ABS sensor failures at the same location.
 
beerdog said:
Her eis what i am dealing with.

I had a ABS sensor for my 98 go bad. I got a replacement and it failed a week later. I also think I had a bad battery negative cable which I just replaced. Do you think a bad battery ground could have been causing some funky voltages to hit the sensor? Anyone else ever experience multiple ABS sensor failures at the same location.
Click to expand...

Hi.
A bad neg battery cable will cause circuits to search for another earth. This is why some cars get through throttle cables rapidly! The inner cable takes the current and heats up and melts the inner cable-causing sticking and rapid wear and snapping!

Can you imagine a starter motor current of 130 amps or more going through the case of a PCM?!!

I doubt that is the cause of any failures. There is no earth return through our ABS sensors.

interestingly, if a more modern "active" abs sensors resistance is checked with a digital multimeter it will be destroyed. A scope must be used to check any output.
In fact this is really the only way to diagnose modern systems - not just ABS.

One thing to watch out for is an AC "ripple" from the alternator (caused by a diode that is not rectifying properly). Anything more than 0.5 volts AC when the engine is running can cause really unusual symptoms.

See http://www.pvv.org/~syljua/merc/TooSeptST07.pdf for an insight.

The school physics lessons where a wire is moved through a magnetic field and a current is induced into it is a good explanation of how the ABS sensor works.

Andy.
 
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