Testing of ABS Speed Sensors

[JHZR2]

Per some of my other threads, I’ve had terrible issues with ABS faults, and specifically sensors.

I tried to diagnose my right front (the current one throwing a code), and cannot get a value. I tried one of the ones I pulled, thinking maybe they weren’t bad. Nothing. So then ai went to a corner that was good - still no reading.

Using a good quality fluke meter, good leads and know I’m in contact with the pins in the sensor harness.

Is there an SOP for testing these? Thought you use an ohmmeter and were supposed to see something like 1000 or 1400 Ohms, May be wrong though.

Anyone know?

[dtla1]

I don't have the answers you are looking for, but did want to recommend you try to swap out the battery. Dying batteries cause some of the weirdest issues, doesn't hurt to check.

[Edrift]

Originally Posted by JHZR2

Per some of my other threads, I’ve had terrible issues with ABS faults, and specifically sensors.

I tried to diagnose my right front (the current one throwing a code), and cannot get a value. I tried one of the ones I pulled, thinking maybe they weren’t bad. Nothing. So then ai went to a corner that was good - still no reading.

Using a good quality fluke meter, good leads and know I’m in contact with the pins in the sensor harness.

Is there an SOP for testing these? Thought you use an ohmmeter and were supposed to see something like 1000 or 1400 Ohms, May be wrong though.

Anyone know?

You can't use a multimeter add the refresh rate isn't high enough.

You'll need a frequency generator and oscilloscope.
Wheel speed sensors generally use pulse width modulation.

It's pretty hard to test manually without the right tools.

I haven't looked at the BMW sensors specifically, but is there an encoder ring too? Looks like a mini disc rotor full of holes.
If so, perhaps that is dirty?

What error is it throwing?
Can you try interchanging a working one for that same position that is throwing a fault?
That way you can see if the fault follows the sensor or if it's the DSC ECU instead.

[Rmtt]

From what I understand there is an encoder and they do get dirty. But you would need to measure frequency as mentioned above as its a high PWM range it's looking in.

I haven't looked for any specs on what the frequency is....but I would check the encoder. I think they call it a reluctor ring.

[WDE82]

I doubt these are VR sensors (variable reluctance). They're probably hall effect sensors.

These sensors switch very fast. If you're passing a ferrous object over the tip, your multimeter may not pick it up. Some are pulse type and have a pulse anywhere from 30 us to 300 us (this is cars in general). Others output the "gear" profile that they pass over in square wave form. So you should see a high and low voltage output depending on what you pass in front of the sensor.

So if you power it correctly, and hook up a correct load circuit you can test it (need a pull up or down resistor + maybe a 5VDC and 12VDC source). But you are probably not doing that. Chances are if the computer is giving an error for a particular wheel sensor, it is the sensor itself. Just replace it and stop wasting your time. If you insist on testing, then just swap two of the sensors around and see if the error follows (just like testing a coil pack for misfiring).

I literally just left a job and an engineer from the past 7 years where we made millions of cam, crank, and transmission speed sensors a year.

[Dackelone]

You will need a scan tool to see the wheel speed values.

[Southjersey128]

If the problem is in the rear, check the tone ring on the CV joint for rust. I've seen them rust to the point that it breaks the tone ring itself or fills in the gap that the sensor is supposed to read. Hope this helps...just realized you said the problem was in the front, sorry. Still good info for future reference i guess?