UK-POLOS.NET - THE VW Polo Forum

JeyLn wrote: Mon Jun 09, 2025 9:00 pm

RUM4MO wrote: Mon Jun 09, 2025 7:26 pm.

The front left was 4k,166 ohms and the rear left 0.748 ohms.

One question, shouldn't the resistance readings be done with battery off ?
I remember I read somewhere it should be done like that otherwise it will damage the car electronics?

I respect your reason/logic for removing the battery before checking the 4 ABS input channels impedance, so to keep you happy then do that.

The low resistance of that rear left sensor, to me, means that it is faulty, the ABS controller will have been designed to expect similar sensor impedance from all 4 sensors.

I seem to have checked a single 2015 6C ABS sensor when it was new, and recorded a value of 4.???M ohms - while my 2011 Audi S4 ABS sensors are 497>576 ohms. Maybe I should check the spare new Polo sensor again!

Edit:- These ABS controller are more robust than you might think, they need to survive their input channels having a short across them, and even that short also going to the body earth.

After you have replaced this faulty sensor, you might find that an ABS related fault still exists "elsewhere", don't worry too much about that, take the car for a short drive, then if necessary clear all remaining faults and they should now stay away.

I've rechecked the DC impedance of the spare Bosch front left ABS wheel sensor that I have, and I was correct, it measures 1.47M ohms - and your car, according to ECP, uses the same 4 ABS sensors as my wife's 2015 6C VW Polo 1.2TSI, so I'd expect that your ABS sensors would have similar values.

One thing though, when I plugged that new spare Polo 1.47M ohm sensor into the wiring of my 2011 Audi S4 after its front right sensor failed - or first reporting its failure as I was reversing out of my garage to take it for its MOT (!!!!!), the 2011 Audi S4, whose's ABS sensors are typically 450>570K ohms, was quite happy to have that sensor plugged into it - it did object to its own failed ABS sensor which was heading towards a short circuit.

Tip learned the hard way, don't buy ABS sensors from places like ECP as they cost roughly £70, Progressive Parts sell Bosch ABS sensors for a lot less and send them out quickly!

When I needed an ABS sensor quickly for my wife's 2015 VW Polo 1.2TSI after I ended up breaking one when replacing the front wheel bearings - I probably did the right thing driving to ECP to pick one up, VW were charging roughly £95, the second time, I also might have done the right thing as I felt the need to get my car MOT'd - though I could have handled a few days delay - but that is just an excuse!

The crazy thing is that these VW Polos have 4 different ABS sensors, whereas my 2011 Audi S4 only has 2 different sensors, ie front right is same as rear left and front left is same as rear right.

Since last time I had the car on jack's, I cleaned the metal particles on the rear abs ring and after checking multiple times the front connector, both sensors started reading correctly, every turn by hand it registered speed. Nice.

Well today when I was getting out of the garage no readings on both sensors again, at all.
As I started driving it registered a spike on the front sensor and then the dash lights lit up.

I'm so done with this car, jesus.



Before it was showing errors of range/performance now its just showing mechanical fault for both.

0401-Front Left Wheel Speed Sensor

C101A 07 [137] - Mechanical Failure

0403 - Rear Left Wheel Speed Sensor

C101C 07 [137] - Mechanical Failure

Here I go again lift up this goddamn car I lost count how many times.

I will check every sensor and connector and will post them here.

And yes it's so stupid they use 4 different sensors, if it was just 2 it would be much easier to know if it's the sensor just by swapping.


EDIT: Put the rear of the car on ramps as I couldn't bother jacking up. Removed both sensors the left one was reading 338 ohms, yesterday it was reading 0.748 ohms. The right one gave OL I think it means open loop ?

I don't know what to think anymore, I touched with the probes from every angle possible, nothing, my only thoughts were did I just kill another sensor ? Keep in mind I never shorted the probes with the pins so I thought I was damaging the sensors just by unplugging the connectors with battery connected.
Truth is in the Elsa manual it always mentions disconnecting the battery when working with electronics but having to do that just for unplugging a connector seems excessive?

Plugged them back, didn't even bother reading the front ones. Go for another test drive.

Front left started working right away without me touching it, the rear right is also working correctly although it showed open loop ??? After a few minutes the rear left woke up with many spikes and then started reading correctly together with the other 3.




Drove for like 20 minutes, rough pavement, speed bumps, all kept working fine.

What do you think of all this ? Loose wire inside insulation?

left rear looks like its acting up too much speed difference, and the graph is like of on/off.
Possibly a connection issue

Did you replace the sensor? That's the first thing I would do. Sometimes they just break.

I managed to get a borrowed rear sensor from another polo, although I can't be exactly sure it is indeed the sensor itself because sometimes it works fine, sometimes not but it fixed the problem at least after two test drives.

I then used my sensor on the other polo and the sensor then started registering speed randomly, kinda like the graph in the photo, this with the car standing still. When rotating the wheel by hand it didn't work.

I guess it's safe to say the problem is the sensor ? But what could have happened for it to fail right after installing the new suspension ? Could a damaged wire inside the insulation kill a sensor or make it go crazy ? Because the cable was stretched when I installed the coil spring though no visible damage was made.

Put mine back in, as soon as I turned the ignition on, the speed needle moved, when driving at low speed, the brake pedal started vibrating but no lights turned on the dash.

Called VW to get a quote on both sensors, plus 200€ yikes
Other local parts stores either don't have in stock (only cheap brands) or don't have at all.

I guess I will have to order online.

Some users reported that even sensors from aliexpress worked fine (10-15 eur max)

I just found a set of 4 for 10€, looking at the reviews it even has the oem number and the vw logo ? How is that even possible?
I'm kinda scared of it damaging my ecu or abs though.
But it's very tempting !

Won't get it on time though as car inspection is until the end of this month and I have to get it at least without the dash lights on.

I wouldnt save money on an abs sensor. Get an OEM one. You'll have it at the dealership on Friday and sorts it, by the looks of your findings.

iichel wrote: Wed Jun 11, 2025 5:42 pm I wouldnt save money on an abs sensor. Get an OEM one. You'll have it at the dealership on Friday and sorts it, by the looks of your findings.

This!

You, OP are just wasting time, I've told you already that the measured DC resistance value is far too low, in my limited experience, these ABS sensors are quite robust so should not get wrecked with anyone checking them with a modern high input impedance multi meter.

What can and does happen with older cars, is that corrosion builds up on the wheel bearing assembly, and this then becomes an issue as it contacts the "finger" of the ABS wheel sensor, and when it does that, it wears through the plastic enclosure and then contacts the coils inside - and that drops the measured DC impedance down to near enough zero.

Another possible issue, on some cars, is wheel bearing failure/wearing and that also allows this same "finger" to end up getting worn down and so shorting out, providing little or no steady signal from that wheel.

While the official ABS controller supplier is Bosch, at the factories, it tends to be the supplier of "that area" of the car that the fitted ABS sensor is branded with - now who actually manufactures these TRW or similar like ATE ABS sensors - I can't say, I tend to source Bosch branded items, but do a lot of searching to find somewhere selling them at a sensible price, as I said in an early reply.

You are lucky if you actually remove ABS wheels sensors intact, in UK and probably many other Northern European countries - they will usually break when you try to remove them.

Apply some non conducting high temperature grease to the new ABS sensor and hub area, so that they can be removed "later". At factory no grease is used, in workshop manuals the recommendation is now to apply grease when replacing them.

Edited to add "ATE" to the list of possible ABS sensor suppliers to car assembly plants.

Both wheel speed sensors are intact, there's no wear on them. And they did come greased with some thick paste on the entire part that sits inside the hub from factory.
The borrowed sensor even had more of that thick paste/grease that part of it was rubbing on the abs ring, all mixed with dirt and brake dust.

What about the right rear sensor working fine and reading OL on the multimeter though, isn't that weird ?

JeyLn wrote: Wed Jun 11, 2025 5:38 pm I just found a set of 4 for 10€, looking at the reviews it even has the oem number and the vw logo ? How is that even possible?
I'm kinda scared of it damaging my ecu or abs though.
But it's very tempting !

Won't get it on time though as car inspection is until the end of this month and I have to get it at least without the dash lights on.

because vw sources parts from China, bosch parts sank in quality

amer6R wrote: Wed Jun 11, 2025 9:19 pm

JeyLn wrote: Wed Jun 11, 2025 5:38 pm I just found a set of 4 for 10€, looking at the reviews it even has the oem number and the vw logo ? How is that even possible?
I'm kinda scared of it damaging my ecu or abs though.
But it's very tempting !

Won't get it on time though as car inspection is until the end of this month and I have to get it at least without the dash lights on.

because vw sources parts from China, bosch parts sank in quality

Also remember that VW Group do actually manufacture cars in China mainly for local sales/use.

Also, not many part of the world are willing or able to manufacture parts nowadays, so it is China, India or nowhere.

I've bought some Lemforder parts - same as fitted to my 2011 Audi S4 but with the Audi branding ground off them, some are "made in Germany" and sadly some are "made in China". I know that if the design has been proven and the manufacturing process has been proven and that if random quality sampling is being carried out - then why worry, but like it sounds you do and so do I.

So, to round up, sort of:- £3.00 from China/India, £12.00 from UK based trusted parts supplier, £65.00 from UK based major car parts supplier and £95.00 from UK based VW Group dealerships, all for seemingly the same basic part - hummmm.

I know that the UK based VW Group dealership will be what any sensible workshop will like to buy from - or the similar UK based TPS trade outlets, but the customer will end up paying the full VW Group retail price when he gets billed by the workshop, warranty claims will be easy for all parties - but for DIYers in UK is the extra £83.00 worth that convenience - but there again, if you just need your car back on the road as soon as possible, then paying the extra money to walk in and walk out with the correct part must have some monetary value - no?

Lemforder also became quality