30 minutes ago, Pete_Ex-Wino said:

Fair enough. 🙂

Again! 😁

I just had a scan through my online manual and here in lies the answer, these sensors are indeed active ones, even though they only have 2 connections, so that means that the ABS controller itself forms the load effect for them to operate?

Beyond me, but looks like they maybe generate a voltage?

No, they take the incoming 12V supply and then via the internal chips superimpose a square wave signal whose frequency is dependent on the wheel speed, whereas the ones with a coil and a magnetic core are passive devices that actually do produce a weak AC voltage which is a sine wave and does not require a 12v supply, unlike active sensors.

Still beyond me. 

To an extent it is to me and electronics is my hobby, I love to repair audio equipment and also test gear, but I have to confess that modern digital electronics leave me a little confused.😁

Edited 19 April, 20224 yr by Graham Butcher

I think if I read this in the morning I'll probably understand it:

https://www.tiepie-automotive.com/en/articles/abs-sensor-hall

Oh, thats useful information, thanks for the link 👍

Scroll down to page 16 & 17 it shows the two different types of sensors SSP+264+++ Brake assist system.pdf

32 minutes ago, nige8021 said:

Scroll down to page 16 & 17 it shows the two different types of sensors SSP+264+++ Brake assist system.pdf

Yes, the inductive one, page 16 is the one where a multimeter may be used to see if the coil is intact or has a broken connection and page 17 is a version of the active sensor (hall effect) but is in fact the older style with 3 wires. It also says that these active sensors are better because they can detect much slower wheel speeds and are therefore safer as they will react far quicker to speed variations, which could be the lifesaver in some circumstances.

10 minutes ago, Graham Butcher said:

page 17 is a version of the active sensor (hall effect) but is in fact the older style with 3 wires. It also says that these active sensors are better because they can detect much slower wheel speeds and are therefore safer as they will react far quicker to speed variations, which could be the lifesaver in some circumstances.

 

If you look at the picture it shows the 3 connections from the Hall sensor connected to give a 2 wire output, the supply voltage and the "Hall voltage (square wave signal?)" 

43 minutes ago, nige8021 said:

 

If you look at the picture it shows the 3 connections from the Hall sensor connected to give a 2 wire output, the supply voltage and the "Hall voltage (square wave signal?)" 

No, that is a 3 wire sensor that uses 1 wire of the supply as the common for the Hall voltage second wire. This link actually shows the connection of a 2 wire sensor and the third part of the sensor circuitry is housed inside the ABS control module, which means if that part fails it will greatly increase the cost or repair as that unit will need replacing and hence why I have decided against a DIY repair because my live data testing shows the wheel sensor as working correctly, indicating that the fault more than likely exists with the control module itself 😟

https://www.tiepie-automotive.com/en/articles/abs-sensor-hall

I stumbled across this interesting video which shows that sometimes you can catch a cold when you opt for what is perceived to be a premium replacement for a faulty sensor, I wonder how many times people fallen into this kind of trap?

 

 

Since I washed my car the problem with regard to the dashboard lighting like a Christmas tree and giving an indication that the N/S/R wheel speed sensor was faulty, I have not any reoccurrence of that problem. Prior to that, it was covered with the sand dust that we experienced in the South, could that have been causing the problems?

 

It is booked into my local VWAuditech centre in the morning for a diagnostic check over, the warnings have long gone, hopefully however, they might be held in the ECU's memory so that they can retrieve them. I have not cleared them this time.

Hi there, I am sorry to hear your having car troubles. Regarding the sensor issue, maybe you covered this in a previous post I missed but was the magnetic ring corroded badly? If it was then the magnetic field produced by it will be lessened resulting in a weaker signal and possible error. 

Also, do you know if the brakes have ever overheated or got very hot? If they did its potentially possible the abs ring got slightly demagnetised again causing an error.

One more possibility I can think of is if the wheel bearing is failing maybe the sensor ring moves further away from the sensor to play in the bearing causing it to feel a weaker magnetic field and thus throw an error. 

1 hour ago, fabia88 said:

Hi there, I am sorry to hear your having car troubles. Regarding the sensor issue, maybe you covered this in a previous post I missed but was the magnetic ring corroded badly? If it was then the magnetic field produced by it will be lessened resulting in a weaker signal and possible error. 

Also, do you know if the brakes have ever overheated or got very hot? If they did its potentially possible the abs ring got slightly demagnetised again causing an error.

One more possibility I can think of is if the wheel bearing is failing maybe the sensor ring moves further away from the sensor to play in the bearing causing it to feel a weaker magnetic field and thus throw an error. 

 

Thank you for the reply and suggestions, I don't know if the ring is corroded or not, but I suspect not, I have tested the sensor loop for all the wheels pretty extensively by using the live data reports on my OBD2 dongle, and it reports all wheel speeds the same unless I'm on bend or a corner. I've pulled the N/S/R sensor, and it looks to be perfectly fine as well, no sign of anything rubbing on the end where it is running close to the magnetic ring and all connections are clean and making good contact.

 

Wheel bearing felt just fine and has zero rumbling or grumbling noises when spinning the wheel, and no, the brakes have never got hot, its a low mileage car and its been with me since I collected it new from the dealer's in 2013, so I know its history well. All the time I had the sand dust on the car, I was getting this problem, since washing the car, not a thing, so I'm taking it into the specialist today, so lets see what their test equipment can detect. I'll post on here what their finding is, but at the moment it is behaving itself.

Garage just rang, and their system does indeed point to the N/S/R sensor, so they are replacing both the magnetic ring and the sensor tomorrow (they have to order them in) so we shall know further tomorrow.

Ok, update time. I initially booked the car for a thorough diagnostic check as the garage claimed that they have the self same system as used by the factory for the ECU's etc, while I only have the plug-in dongle from Carista. I had also taken screen prints of the various readouts from the Carista and printed them out to assist the garage, and left these with the car for them in case there was no error codes stored in the memory.

 

When they had done the tests they called me to inform me that their tests had shown them the problem was the N/S/R sensor as this was the only code stored and did I want them to replace the sensor, I said yes and asked if that would also be the magnetic ring gear, but I didn't get a definitive answer on that, or at least I could understand. They had to order a sensor in for the following morning, so the car was left with them overnight.

 

Today I was called and told that the car was ready for collection and the cost £239, £41.25 was diagnostic checking, £79.92 was the cost of the sensor and £78 was the labour and the rest was VAT @ 20%.

 

I enquired if they did the magnetic ring on the hub, and they said no, 99% of the time it is the actual sensor that fails. I queried that as the live data testing via the Carista tool showed all speed sensors to be working OK and the only they differed was while cornering, which you'd expect anyway. I was told that they question the accuracy of the plug-in Carista units and again stated that their system was the same as the factory uses and so was better?? They also said the magnetic ring was built into the wheel bearing? Strange as it is, my understanding that is replaceable on its own and not part of the wheel bearing, am I wrong on that point?

 

I was however given a 2-year warranty on the work and told to just see what happens.

 

Had I been fully aware that they were not going to replace or at least inspect the magnetic ring, I would have replaced the sensor myself.

 

Oh well, its done now, just have to wait if the same thing occurs again, the last time I had the dash alert for the sensor was on the 18th April.

 

I hate seeing these prices £239 for a £30 sensor and fifteen minutes work

Your lucky they didnt replace the rear wheel bearing they would of charged you about a grand 

The magnetic ring is built into the rear of the wheel bearing on these models

 

Gee, thanks for this, shows just how we motorists can be suckered in for sure.  What actually Gauls me is that I actually purchased a replacement sensor from GSF Auto parts in preparation to replace it, after I had already pulled the old sensor out, checked it using my multimeter and discovered that it appeared to be OK. This was after watching this video I checked the sensor as shown and it was OK. So I returned the new sensor for a refund, but only after refitting the old sensor and doing a live data test and it was giving me the same speeds as the other 3 wheels, thus I assumed that I worse issues and booked it in for a full diagnostic check using more sophisticated equipment, the rest is history.