Dealer read fault memory codes : wheel speed sensor

[dazz]

Hi

I had the dealer read my car's fault codes. See attached. That is all I asked them to do, and that was expensive enough.
They wanted to do diagnostics, but for waaaayyy too much money.

The reason I asked them to read the fault codes was because I was getting 3 orange warning lights, all related to speed.
The symptoms are consistent with a bad wheel speed sensor or module.

The report indicates module or speed sensor faults. I suspect the sensor, only because it is located in a hostile location.

Do these cars have a history of wheel speed module/sensor failures?

[iichel]

Yes, it's possible for a sensor to fail. Another possibility is for the wiring to be damaged.

[dazz]

Hi
OK I removed and tested both front wheel speed sensors.

The left sensor measures 2.2kohms.
The right sensor measures 28Meg ohms.

If the sensor is a coil, then the left one looks OK and the right one is faulty. However that is the opposite to the VW code report.

I also measure the voltage from the car loom when the ignition was switched to run, but engine off. The sensor was marked +ve and -ve.
Left connector -1.48VDC
Right connector -2VDC.

That indicates the wiring is OK. Not sure about the voltage values. I expected to see positive volts and more of them.

I read someone had similar symptoms that turned out to be a bad ECU earth. Where would I find that? Note that salt is not used on roads where I live, so corrosion is not too much of a problem.

So one of the wheel speed sensors is not like the other. I suspect the right one is faulty, but that is not what the mechanics VW scanner said. It is possible I have multiple faults, but the car drives OK.

Any hints?

[ciclo]

Hi
Any hints?

Hi
I would buy and install two new front speed sensors (L&R) in hopes of fixing the problem.



They have been replaced by new ones with B letter at the end of the reference number, ... can be found in various places at very reasonable prices.

[amer6R]

If you have any diagnostic tool that can read wheel speed sensors, connect it, and turn the wheel by hand and see if the lice data changes.
What wheel doesnt thats the one

[RUM4MO]

The first time I had wheel sensor trouble, I think that I connected a high input impendence digital voltmeter to each wheel sensor and rotated each wheel at the same speed.
They all gave out roughly the same AC voltage, so they were all okay, I then checked the input impedance of each of the 4 wheel sensor inputs on the ABS controller - one was O/C, this was on a 1991 Vauxhall Cav GSI 4X4 that was still under approved used car warranty - the dealership had replaced one front sensor, and the car's ABS was still faulty, they accepted it back in and replaced the other front sensor, some result, it was weekend in winter and I was getting annoyed, so checked things over myself and reported back to them what I thought was wrong, they replaced both front sensors again, same result, next day they replaced both rear sensors, when I phoned them, as usual, after driving home after work, they same that they would order in an ABS controller, replacing that a week later sorted that car out! Trouble seemed to be that that early model of Bosch ABS controller did not any diagnostic support at dealership level - although each time they said they did have and used diagnostic equipment!

Anyway OP, lucky you if you managed to remove both front ABS sensors intact - I failed to avoid cracking one when replacing a front wheel bearing on my wife's August 2015 VW Polo!

As hopefully an outside possibility for having wheel sensor issues, or loss of good data, a worn wheel bearing can cause the loss of good wheel speed data as the distance between the sensor and the magnetic insert on the wheel bearing assembly is changing/varying.

[iichel]

Did you measure the wheel speed sensor in situ or did you remove it before?

They are supposed to read magnetic fields from the hub. So variations in measurements are to be expected.

[amer6R]

yeah you could definitely test with multimeter, while you rotate the hub. - or move a metalic object infront of it
You can find tutorials on internet just search multimeter electro magnetic wheel sensor test.
Multimeter can be bought for cheap

[dazz]

Hi
I have ordered a scan tool from Aliexpress. The local VW dealer charges more $$ than the cost of the scanner I have purchased. They charge a lot more to look at the report and say what is wrong. I won't have the scanner until later in the week.

I am an Electronics Engineer, so I setup a test rig to test the sensor. This was an electric drill with a 10cm bar held in the chuck with a bolt that passed thru the bar. I placed a strong magnet on the end of the bar. Turning the drill on caused the bar and magnet to sweep around in a circular motion. This simulates the magnet on a hub.

I don't know if the VW wheel speed sensors are a coil or a Hall effect sensor. Being only two wire, much more likely they are simple coils. Sweeping a magnet across them should produce and AC voltage.

I would expect a Hall effect sensor to have at least 3 wires. Hall effect device output is dependent on the lines of magnetic field being correctly aligned with the sensor.

I used my oscilloscope to measure the sensor output. I got no output from the faulty sensor, but the ohm reading seemed OK.
The ohm reading on the right sensor was suspiciously high.

I left at that. I will investigate further when I have the scanner.

[RUM4MO]

Yes, I reckon that they are just a coil, although I did use a high input impedance multi meter on the ones on my old Cav GSI 4X4, I also borrowed an oscilloscope to check all four wheel sensor outputs.

We are lucky that things have moved on, back in 1994, the ABS sensors in some cars were just aluminium cans with coils inside, they were fitted at the factory with plastic sleeves to stop corrosion as they were fitted in iron castings on the wheel carriers, that was good when new, but after my main dealer replaced all 4, the front ones twice, all the plastic sleeves were removed along with the original wheel sensors - so, maybe 5 years down the line, the first of these unprotected wheel sensors failed, the aluminium can disliking being in close contact with the iron castings, so the resulting corrosion forced the aluminium covers/can in against the coils and it was game over! The other 3 wheel sensors were now ticking time bombs, but they lasted until after I sold that car on in May 2000!

[dazz]

Hi
I have decided to try some wheel speed sensors from Aliexpress. My plan was to buy a right front sensor.
The car is telling me the left front sensor is faulty, but a physical check faults the right front.

I am wondering if my car has left/right mixed up because my radio (Chinese android unit) also reports the wrong hand. For example, when the left door is open, the head unit displays a right door open. I used to think this was because of Chinese software. Now I have reason to suspect the car.

I have tried out my moderately priced, not the best ANCEL BD500 OBD2 Scanner Bluetooth IOS Android Car Intelligent Diagnostic Tool. It works as advertised. It has a nice user interface. It has done everything that I have expected of it. It will reset maintenance/inspection periods. I don't know if it will allow programming of module features. I did not buy the scanner for that and I haven't tried to look for that sort of feature. I am a happy customer. I only have to avoid one trip to the dealer to print off the error codes and the scanner is paid for.

The only other scanner I have is a hacked version of the BMW factory/dealer code.

Anyway, I could not find a single sensor on Aliexpress. I could only find sets of 4 like here : https://www.aliexpress.com/item/4000495 ... ciLytYS6tO

It is most likely these are made in the same factory on the same production line as the genuine VW parts. It is possible they are factory seconds. They are so cheap that it is worth the risk to try them out.

[dazz]

Hi
I installed my Aliexpress sourced wheel speed sensor a few days ago. It is working perfectly and all error messages/lights have gone.

I checked the resistance of all the Aliexpress sensors before I fitted the left hand sensor. They all read about 850kohm. This is much greater than I expected, but about the same as the factory right hand sensor fitted to my car.
I suspect the sensors include zener diodes (or similar). The output of the sensor coils would need to exceed the zener voltage before the sensor produced a voltage output. This would be a simple but effective method of reducing electrical noise.

In contrast, the faulty sensor reads about 2.5kohm, about what I expected from just a coil sensor.

So in summary, the Aliexpress sensors look exactly the same as the factory fitted sensors. The one fitted works perfectly and saved me a large amount of money.
I still have 3 sensors left, so if another fails, I have a spare on-hand.

[ciclo]

Congrats! Wise decision.
When these parts/sensors fail it is better to renew them.

[dazz]

Hi
After a few months, the Aliexpress sensor is still working perfectly.