ABS light on Scan tool recommendation

[myozone]

Hello,
I have a 9n3 1.4 TDi5 door and recently the ABS light has come on, It's probably a wheel sensor and therefore need to find which one.
I've looked at OBD2 CAN scan tools but it appears to be a bit of a lottery to which ones work. Does any know of one that works for reading ABS with my Polo - I know of VAG-Com but that's out of my price range. Or is there someone near to Helston in Cornwall that could help ?

Thanks.

[Maarten]

The old version of VCDS will work on 9N3
VAG-COM 4.11 if I remember correct

The Aliexpress clones will also do the trick on these older model cars.
Just use offline.

Best would be VCDS full, but I know, pricy

[myozone]

Oh ok, Thanks. Failing that do you know the resistance of a good ABS wheel sensor ?

[RUM4MO]

1.464M ohms, that is a new one that I have, genuine VW Group part.

Remember as this is just a pickup device, a working one's impedance could vary quite a bit from what I measured.

Measured using a Fluke 77 Model 4 by the way, so not just a cheap meter.

Edit:- so if it is very low or looks like being open circuit, then it will not be working too well!

[myozone]

That's a lot higher than I would have guessed (50-200 Kohms) Yes, it's just a coil of wire over an iron core and a chopper disk on the wheel hub. Spinning the wheel may generate a small voltage?

I'm into electronics for years so have a good knowledge...

I looked at Vag tools on Ali for about £60 but I'm not sure about that's a good idea or not ?

[RUM4MO]

Yes, a high input impedance DMM should be able to detect a small signal, so if you do that with each sensor you should be able to work out if one is completely dead.

I ended up doing that with a 1991 VX Cav GSI 2000 16V 4X4, its ABS system went faulty the first winter that I owned it from being under 2 years old. Dealer's workshop said "faulty front near side sensor" replaced that and sent me on my way, 100 yards or so later same problem! As I worked near by I handed it back in next day and asked to make sure that someone actually test drove it, "faulty front off side sensor" - same thing, returned next day! This day "replaced both front ABS sensors" and it failed again, each time I was assured that the chief tech and the workshop manager took it out for a test drive. Now it was the weekend, so I borrowed an oscilloscope from work, checked the output from each of the 4 sensors, they all provided a clean and similar output waveform. So, as the ABS controller was located inside the passenger side "frame" I unplugged the connector and after working out which pins were the individual channel inputs, checked all 4 channels input impedance - 3 looked okay and 1 looked open circuit! With this info back to workshop on Monday "we have replaced both rear sensors and both front sensors again" by now I was getting a bit concerned over the cost of repair as "doing it this way will be cheaper than you claiming it through the VX used car warranty"!? I demanded to know how they were fault finding this system, they quickly replied that they had all the necessary testing equipment and this system self tests - I replied, "lies, this is an earlier system and it does not have an self testing built into it". So, after another day they ordered in a new ABS controller, next visit, I hung around as replacing that controller, with its easy access would only take 15 minutes max - problem solved and I only paid for 50% of the cost of the first ABS sensor! Dealership workshops and everything that is not straight forward is not good for the customer. Final note, as VX fitted PTFE or similar insulating/isolating sleeves over the bodies of these ABS sensors to avoid any issues between the alloy can casings and the cast iron hub assemblies, and that clever dealership probably threw them in the bin along with the good faulty sensors, it was only a few years before the first new ABS sensor failed - and the Bosch workshop that diagnosed it and replaced, said why it had failed, and then I told him my sad tale, and waited for the sensor to fail!

[myozone]

RUM4MO Wow, Very interesting read thanks for passing it on. I do have an oscilloscope but it's a old CRT type and not easy to get to the car. I'll have fiddle my DMM sometime and lookit a cloned scantool - most likely a waste of money

I've been a ham for 40+ years so know a bit of electronics

The car is 17 years and has been VERY reliable, I only replaced the front discs and pads recently from new at 73,000 miles. The electric steering pump went which sounded like a H bridge FET fault and the starter motor which was the wire braid going onto the side had corroded and got hot - a common fault I believe.

[impvan]

I'm /pretty/ sure that the ABS pickup isn't just a coil on the 9N3. ISTR when testing mine that it puts out a nice clean square wave, so probably a Hall sensor.

Resistance checks wont help. Do a voltage test between signal wire and chassis, and look for the voltage jumping as you slowly turn the roadwheel.

Or ~ just use the free version of VCDS, it works fine with the KBus signals on pre-6C Polos

[myozone]

Ah ok good to know.

I ordered a VCDS from Aliexpress and guess what it didn't work just basic OBDII. I've returned it today so fingers crossed on a refund. I paid £71 for it ...

Anyone know of a scantool prefable VCDS that works ?. Most of the Aliexpress ones appear to be the same thing from 'different ?' sellers.

@impvan Where did you get your scan tool and software from please and is it the Atmel162 or STM32F429 or something else ?