Technical Stuck faulty ABS sensor in the front wheel hub (55700425 sending unit ANT) - how to replace them?

[Zardo]

Hi,

I'd like to replace the two "sending units" for the anti-locking system in the front wheel hubs, that is the two front ABS sensors of my 2010 Abarth Punto Evo.

Mine are stuck in place and even with all the force of my feeble hands, I was unable to get the sensor out of the hole. (Yes I did unscrew the bolt first).

I found this video:



Looks like if its a common problem for those sensors to get stuck over the years.

I was wondering if it's actually easier to replace the whole wheel hub and bearing? Since drilling the sensor out will generate a lot of metallic particles inside the wheel hub and will contaminate the ABS ring. So there's not much chance of getting a clean signal ever again without cleaning out the debris first. Also, in order to clean the hub it would need to be disassembled anyway?

Go to 1 hour 1 min and 25 seconds in the video link to see what I mean.

The reason why I'd like to replace the sensors is that there's a fault code and I lost the ESP and hill-holder (and the ABS probably too). I already repaired a damaged sensor cable where it was hit be the tyre when cornering hard and the fault went away for a few months but later came back so in theory maybe it's only the cable again.

 

[bugsymike]

Hi,

I'd like to replace the two "sending units" for the anti-locking system in the front wheel hubs, that is the two front ABS sensors of my 2010 Abarth Punto Evo.

Mine are stuck in place and even with all the force of my feeble hands, I was unable to get the sensor out of the hole. (Yes I did unscrew the bolt first).

I found this video:



Looks like if its a common problem for those sensors to get stuck over the years.

I was wondering if it's actually easier to replace the whole wheel hub and bearing? Since drilling the sensor out will generate a lot of metallic particles inside the wheel hub and will contaminate the ABS ring. So there's not much chance of getting a clean signal ever again without cleaning out the debris first. Also, in order to clean the hub it would need to be disassembled anyway?

Go to 1 hour 1 min and 25 seconds in the video link to see what I mean.

The reason why I'd like to replace the sensors is that there's a fault code and I lost the ESP and hill-holder (and the ABS probably too). I already repaired a damaged sensor cable where it was hit be the tyre when cornering hard and the fault went away for a few months but later came back so in theory maybe it's only the cable again.

Ideally you would confirm fault is where you think it is using MES or similar diagnostics , this will prevent wasting money unnecessarily.
Usually plenty of lubrication and careful leverage will extract old ABS sensor and then vacuum out any debris.
The main thing it DO NOT USE ANYTHING MAGNETIC!!! as that will destroy the ABS ring in the wheel bearing and then you will be replacing the bearing etc.

 

[Zardo]

Thanks.

I have the AlfaOBD on my smartphone combined with a bluetooth OBD reader and the set of cables for FIAT.

Maybe checking the bus with an old analog oscilloscope (230 Volts) by connecting it to the cable connector of the car in order to see if the car is sending any signals to the sensor on the bus (or if for some reason there are no signals or voltage) would also be helpful, however I would need to figure out how to send a voltage to the sensor once the cable is disconnected from the car. It's probably 12 V? Or is it passive?

Maybe a test with a voltmeter would be sufficient? I have an unused new sensor which I could check for comparision.

I found this description for a Punto Evo M.Y. 2012 (I don't have an electronic workshop manual for my Abarth, unfortunately):

Measuring the wheel sensor signal

Select the following end of scale on the voltmeter:
Voltage: 20.0 V f.s.
Time Base: 2 seconds
Turn the wheel manually and when the rotation speed reaches 4-6 Km/h press the "Start" button on the Examiner remembering that during the downloading, manual
acceleration or braking of the wheel must not take place.

To carry out the necessary download, disconnect everything and then start the ABS control unit test, delete any errors created during download (interference on signal speeds,
rear left speed sensor not plausible, ...)
N.B. No battery charge should be connected during the signal download.

Reading the signals
The voltage value of a wheel sensor should vary continuously and evenly.

Unfortunately, I don't have the FIAT Examiner hardware. There are some graphs which show that, when the wheel is manually turned with a speed of about 4-6 km/h, the sensor signal should be a square wave moving between 9.6 and 10.6 Volts and it should be steady without any "signal holes" (except if the movement of the wheel stops).

 

[bugsymike]

Thanks.

I have the AlfaOBD on my smartphone combined with a bluetooth OBD reader and the set of cables for FIAT.

Maybe checking the bus with an old analog oscilloscope (230 Volts) by connecting it to the cable connector of the car in order to see if the car is sending any signals to the sensor on the bus (or if for some reason there are no signals or voltage) would also be helpful, however I would need to figure out how to send a voltage to the sensor once the cable is disconnected from the car. It's probably 12 V? Or is it passive?

Maybe a test with a voltmeter would be sufficient? I have an unused new sensor which I could check for comparision.

I found this description for a Punto Evo M.Y. 2012 (I don't have an electronic workshop manual for my Abarth, unfortunately):


Unfortunately, I don't have the FIAT Examiner hardware. There are some graphs which show that, when the wheel is manually turned with a speed of about 4-6 km/h, the sensor signal should be a square wave moving between 9.6 and 10.6 Volts and it should be steady without any "signal holes" (except if the movement of the wheel stops).

I would expect your ABS sensor to be active.
You may be able to read a 12 volt supply across the two terminals as a starting guide, maybe compare with the opposite side.
Generally if error codes deleted and it is an active sensor the error will return when you move off if at the wheel , assuming you have a voltage across the two pins from the loom.
I had a 4x4 Skoda that read 11.5 approx volts on o/s and 8 volts at near side due to a wiring loom fault.
This did as you have found cause ESP, hillholder and ABS faults.
I have not tried an old oscilloscope, so no knowledge in that direction, however a full version of MES or Alfaobd etc. should record all four wheel ABS sensors as you drive.

 

[jackwhoo]

Can alfaobd show each wheel speed?
If yes drive car look to see if wheel speeds the same.

Do that BEFORE replacing parts

 

[Zardo]

Thanks. I'll check what AlfaOBD can do and if there is a voltage provided to the sensor. Instead of the old analog oscilloscope which is rather clumsy and needs 230 V, I ordered a digital multimeter with an integrated oscilloscope and memory to record signals.

After some more internet research, I found that the sensor must indeed be active and comes with its own digital logic. There should be +12 V and the square wave return signal of the sensor (only when the brace disk actually rotates). Disconnecting the sensor and bridging the gap with a probe or croc cable should provide easy access to test the signal pattern whilst manually rotating the brake disk after the wheel has been removed. I'll do some tests whilst putting the winter wheels on. A good opportunity to also check the cable visually for damages.

Thanks for the help. I should be back with some results soon.

 

[bugsymike]

Thanks. I'll check what AlfaOBD can do and if there is a voltage provided to the sensor. Instead of the old analog oscilloscope which is rather clumsy and needs 230 V, I ordered a digital multimeter with an integrated oscilloscope and memory to record signals.

After some more internet research, I found that the sensor must indeed be active and comes with its own digital logic. There should be +12 V and the square wave return signal of the sensor (only when the brace disk actually rotates). Disconnecting the sensor and bridging the gap with a probe or croc cable should provide easy access to test the signal pattern whilst manually rotating the brake disk after the wheel has been removed. I'll do some tests whilst putting the winter wheels on. A good opportunity to also check the cable visually for damages.

Thanks for the help. I should be back with some results soon.

Basically what I mentioned earlier, active, 12volts and error shows when disc rotates/car moves.