Wheel speed sensor fault.

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Rfmotors1
TwoWaves
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Posts: 80
Joined: Fri Aug 31, 2012 8:14 am

Wheel speed sensor fault.

Post by Rfmotors1 »

Hello,

I would like to share one older case where the vehicle returned few times with the ABS warning light ON.
By following the standard process, the technicians replaced, swapped, cleaned, checked and exhausted all the guided tests before the scope got it's turn.
We have lifted the vehicle, backpined the two rear wheel speed sensors and rotated the wheels. That was all we needed to do and we have found the problem. It was the wheel bearing with magnetic ring which had to be replaced.
Interesting is when we have removed the old wheel bearing and examine it, there was nothing visible, we have even removed the magnetic ring from the bearing to see it inside but it was visually perfect, clean, not any metal chips or uneven distribution of the small magnets.
I am thinking how much time and money could be saved by carry out this easy and simple test in the first place.
PSDATA file to open with Pico 7:
Wheel Speed Sensor.psdata
(2.75 MiB) Downloaded 213 times
Picture with notes:
Wheel speed Sensor.jpg
Last edited by Rfmotors1 on Sun Apr 30, 2023 6:38 am, edited 1 time in total.

Bajzel
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Posts: 1
Joined: Wed Dec 09, 2015 5:16 pm

Re: Wheel speed sensor fault.

Post by Bajzel »

Hello, some time ago I had an identical case in Astra J. I left this magnetic ring as a souvenir. The oscilloscope turned out to be worth every penny. Someone might be interested in the photos.
IMG_20230205_152210.jpg
IMG_20230205_152513.jpg
IMG_20230205_152324.jpg

Dan67
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Joined: Wed Sep 14, 2022 4:43 am

Re: Wheel speed sensor fault.

Post by Dan67 »

nice use of the math channel I never thought to use it in that way to make a better visual que.

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Rfmotors1
TwoWaves
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Joined: Fri Aug 31, 2012 8:14 am

Re: Wheel speed sensor fault.

Post by Rfmotors1 »

Hi Bajzel,
Thank you for posting the pictures, this magnetic flux visual foil is fantastic tool, I don't have it but used it few times at training.
It's fantastic tool to prove faulty part to customer, warranty etc. Much more direct as the waveform which not many customers can understand.

Hi Dan67,
I agree, the way to use math channel to find irregularity of signal is not common. I have used it on wheel speed sensors and crank sensors as well. Sometimes this is the easiest way to see the problem.
Simply zooming in may not be visually recognised as fault. The math channel reveals the repetitive pattern so one knows where to look.

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Rfmotors1
TwoWaves
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Posts: 80
Joined: Fri Aug 31, 2012 8:14 am

Re: Wheel speed sensor fault.

Post by Rfmotors1 »

For anyone who is interested, I was lucky, and we had another case where this technique was excellent way to analyse the problem with ABS wheel speed sensor DTC.
Sheel speed sensor MB fault.jpg
It was Mercedes GL this time, however the logic and scoping is the same.
I had to limit the bandwidth to eliminate the noise, probe was backpinned at ABS CM socket. Details in the waveform.

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