Bench Testing ABS Wheel Speed Sensors

[rich.g.williams]

The W203 ABS Wheel Speed Sensors have an IC chip (Hall effect) inside. It's not possible to bench test them with a meter on Volts or Ohms. Attached is a simple circuit showing a way to test them. Please note this is to test them on the bench not connected in any way to the car. Avoid bringing a strong magnet too close to the sensor just in case, a few mm away should show a strong switching response. Any comments appreciated.

 

[mioba]

Its all well and good, but cars tell you there is an error
and your diags tell you its an ABS sensor/

 

[rich.g.williams]

diags tell you its an ABS sensor

Yes the car tells you but do you know that the reluctor ring is as it should be?

This simple sensor test can help differentiate between sensor fault or a reluctor ring fault. Its even possible to set this simple test up in situ (independent of car electronics) and watch the sensor output as you turn the wheel (disk) around by hand. Even count the number of pulses per revolution.

Fitting a new reluctor ring looks like a much harder job than fitting a new ABS wheel speed sensor so its worth knowing.

 

[bembo449]

if the ABS sensors comes out ok then its fairly straight forward to look down the hole and turn the hub to assess the reluctor ring , in my experience its usual obvious when the ring is no long serviceable

 

[rich.g.williams]

if the ABS sensors comes out ok then its fairly straight forward to look down the hole and turn the hub to assess the reluctor ring , in my experience its usual obvious when the ring is no long serviceable

The simple test I am proposing can be done without even removing the ABS Wheel Speed Sensor - just need to unplug it. Irregular pulse width or missing pulses would be the reluctor ring.

Can I detect a certain reluctance here !

 

[ajlsl600]

Yes the car tells you but do you know that the reluctor ring is as it should be?

This simple sensor test can help differentiate between sensor fault or a reluctor ring fault. Its even possible to set this simple test up in situ (independent of car electronics) and watch the sensor output as you turn the wheel (disk) around by hand. Even count the number of pulses per revolution.

Fitting a new reluctor ring looks like a much harder job than fitting a new ABS wheel speed sensor so its worth knowing.

View attachment 84922

I am starting to like, n read with interest ur posts esp anything that may provide guidance on staying away from dealers and being able to test stuff before tipping one's wallet out at some pts store keep going.

 

[ajlsl600]

.I think an a to z on all sensor testing with simplest of testing kit would be a best seller. I suspect that half of those replaced had no fault but it's the simplest thing to change (if cost of doing so is not a factor.) Eg change a suspect sensor to avoid a 200 quid. Diagnostics., many will see changing a wss, or crank sensor a worthwhile risk.

 

[rich.g.williams]

I suspect that half of those replaced had no fault but it's the simplest thing to change

On my car it was a struggle to get the 10mm bolt out (a 3/8" open ended spanner got it loose in the end), apart from that it was easy but the state of the reluctor ring? I didn't fancy taking the disk off etc etc just to get at the reluctor ring for peace of mind, so here is my simple test rig - it needs putting in a box really.




Keep everything away from the car electrics! A 9V PP3 Alkaline battery would probably be enough Volts. Best done with a small portable oscilloscope.

If you have an old ABS Wheel Speed Sensor try it out on that first away from the car. If a sensor works but looks a bit mechanically worse for wear probably best to swop it anyway.

 

[ajlsl600]

Get in box, maybe a green led for good test. Red or nuthin for fail as if not green its a fail! Test, uplug wss connect ur devise 2 min all understood I kept my last 2 wss , I think it was just dirty, but at time I needed to have something ready to fit, as u say the issue I often is getting the retaking bolt out.

 

[supernoodle]

I commend you for testing a component. So many times you read that someone has a fault code for a wheel speed signal, they've replaced the sensor and still have the fault. People forget that the sensor is just one part of the system.

I suggest you watch this guy, some good tutorials on using a scope for testing. I recommend the Picoscope, for the money it's great.

 

[rich.g.williams]

I commend you for testing a component

Thank you for that. With respect the video overcomplicates a very simple test and connects into the live car electrics. It doesn't explain the sensor type and shows a reluctor ring much different to (and much more exposed than) the ring on Mercedes W203.

IMPORTANT THINGS made clear in my text above:-

1. "to test them on the bench not connected in any way to the car"
2. "can be done without even removing the ABS Wheel Speed Sensor"
3. "W203 ABS Wheel Speed Sensors have an IC chip (Hall effect) inside"
4. "Keep everything away from the car electrics!"
5. "A 9V PP3 Alkaline battery would probably be enough Volts"
6. "view on oscilloscope or use a meter to measure the DC offset and the AC switching as magnet is moved"

With so many activities "Keep it Simple" helps so much.




-

 

[rich.g.williams]

For those interested the Hall effect speed sensor is described as "Two-Wire Automotive Hall Effect Sensor" typically manufactured by companies like Diodes Incorporated. Here is a link to some of their information:-

Two-Wire Automotive Hall Effect Sensors


-

 

[supernoodle]

Even if you have tested the sensor on the bench and confirmed it ok I would suggest the next step would have to on the vehicle. If you still had faults you would want to see the signal that the module would be seeing, so that means scope on the vehicle.

 

[rich.g.williams]

Even if you have tested the sensor on the bench and confirmed it ok I would suggest the next step would have to on the vehicle. If you still had faults you would want to see the signal that the module would be seeing, so that means scope on the vehicle.

Its just that I can convince myself that the speed sensor and reluctor ring are working together as intended and I am measuring 48 pulses per revolution of the wheel (I counted them). The four Mercedes speed sensors are very well made parts but they are in a harsh environment attached to the wheel hub.

As a next step - to be honest I hadn't got that far. As a Mercedes car owner I'm nervous about connecting any external electrics to the car (even a battery charger). Even nervous about turning the car ignition on if anything (such as a speed sensor) is disconnected - for fear of some or other controller deciding the world is ending and locking up into a brick.

Seems to me that the only extra thing that "you would want to see the signal that the module would be seeing" does for me is tell me that the controller is powered up and working and that the wiring loom from the controller to the speed sensors is sound (probably info from fault codes anyway).

All that said I do agree with the method you suggest - just the reluctance to connect anything more than a Fluke meter to the car electrics.

 

[rich.g.williams]

Get in box, maybe a green led for good test. Red or nuthin for fail as if not green its a fail! Test, uplug wss connect ur devise 2 min all understood I kept my last 2 wss , I think it was just dirty, but at time I needed to have something ready to fit, as u say the issue I often is getting the retaking bolt out.

With these Two-Wire Automotive Hall Effect Sensor it would be a little difficult to connect LED's to give a pass/fail test. Better to spin the wheel and count the pulses per revolution. Make sure that a loosely mounted sensor (a couple of mm away from the reluctor) still works well (counts all the pulses per revolution) and that's there's nothing "dicky" or intermittent going on.

 

[ajlsl600]

Got u. A simple one of devise that can. Test all the basic sensors currently fitted to most cars would be a great bit of kit.

 

[rich.g.williams]

Got u. A simple one of devise that can. Test all the basic sensors currently fitted to most cars would be a great bit of kit.

My thread is only about W203 wheel speed sensors A2035401317. A2035401417 and A2035400417

 

[ajlsl600]

Got u. Shame, think there is market for above

 

[rich.g.williams]

Mainly interested in my own car, happy to help with info I come across that might be useful for others. My understanding is only a small part of MB tech.

 

[rich.g.williams]

Wheel Speed Sensor update. I replaced the two front wheel speed sensors a few weeks ago but it did not remove the ABS/ESP/BAS errors.

My local MOT garage read the diagnostic fault codes last week and told me that there was a rear offside Wheel Speed Sensor error. This week I got the two rear wheel speed sensors unplugged and tested them both with my PCB setup as described above. The nearside sensor worked fine and produced pulses as expected (I measure 48 pulses per wheel revolution). The offside sensor output looked fine but didn't produce pulses. I pulled it out and repeated the test with a magnet and still no pulses so I fitted a new sensor and it gave the 48 pulses per wheel revolution. (The faulty Wheel Speed Sensor is physically undamaged, shows no signs of wear and is marked as a genuine Mercedes part most likely 20 years old though).

Took the car for a short test drive and the ABS light went out and the ABS/ESP/BAS errors went away - happy days!

The PCB test was useful and confirmed that the reluctor ring was most likely ok, it also looked ok.