ABS Sensor Testing

Hi Everyone

Can anyone out there help, the ABS warning light on my Golf Mk5 is staying on ie. it does not go out after a few seconds of the car ignition being switched on.

I’ve managed to get the sensors out of the wheel hub and I’ve watched a few youtube videos on testing them off the car.

From what I watched they say using a multimeter I should get a reading of 1.5 to 1.7 KΩ across the terminals, but if the reading starts to continuously climb, they are bad.

I’ve tried testing mine and I’m not getting a reading of any sort, should I be getting a reading or are there different types of sensors.

Thanks to anyone who can help

As far as I'm aware ABS sensors are just coils of wire, so you should get a resistance reading through them - are you perhaps not making good contact?, it would be unusual for all to have failed.

Some cars have the Infineon smart Wheel Speed Sensors WSS chips which are a combination of current modulation 7,14, 28mA into 50 Ohms with sync pulse and biphase data. Perhaps combined with ABS sensors.

clive2016 said:

or are there different types of sensors.

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Yes there are different types. After chasing and trying to fix a couple of different GM cars with this type of fault, by changing to new wheel sensors then replacing the connecting wire harnesses, I gave up. And just made sure the brakes were functioning and ignoring the light. Cars were too old to spend any more time on them. As far as I know they are still on the road and still have the light on. Did you check the fault code on the OBD? That will sometimes at least tell you what wheel is having the problem.

Hello Nigel and Tony

Ok let me explain how the ABS light staying on came about.

To start with it was working perfectly fine, but I’ve just had to replace the front struts and springs and in doing so I had to slide the driveshafts out of the hubs and just in case the hub dropped I disconnected the wiring to the wheel sensors.

I also had to replace a window switch and to try the new one out I switched the ignition on and was satisfied the new switch was working ok.

Right back to the struts, I finished fitting the new ones, also putting the driveshafts back into the hubs and reconnecting the wheel sensor wiring, but when I switched the ignition on the ABS warning would not go out.

I’m no expert on wiring hence my coming onto this forum, some time ago on another car I took the airbag off the steering wheel as I had a problem with a light switch stalk.

I switched the ignition on to test the new light switch stalk and found it to be working fine, so I put the airbag etc. back on.

When I turned the ignition on the airbag warning light would not go out.

In the end I had to get a mobile auto electrician to come and look at it for me and he said there was nothing wrong with the airbag but because I’d switched the ignition on whilst the airbag was disconnected the cars’ computer immediately picked it up as a fault.

So, all he had to do was clear the fault, I never did have any further trouble with.

This was some years ago and I know technology has moved on but could the same thing be happening in ABS instance???

I’ve watched one or two youtube videos on testing the wheel sensors off the car with a multimeter and according to them I should get a resistance reading across the two terminals of 1.5 to 1.7KΩ, going on to say if the resistance keeps rising then the sensor is bad.

When I tried it, I did not a reading of any sort and that was on both sensors.

I’ve also spoken to someone else and they said: You can’t test them like that, either with an oscilloscope or by watching the output in measuring blocks using a suitable diagnostic system.

Tony thank you for your explanation, unfortunately most of that went over my head, the car I talking about is a Golf TDi Mk5 and I’ve no idea what type of wheel sensors they have???

Hello Shortbus

No, I haven’t checked it with an OBD2, I’ll guess I’ll have buy one but not too expensive, in any case no doubt the meters with all the bells and whistles I won’t understand.

I suppose if I can narrow it down to just one wheel, I could replace the sensor and hub bearing, as the reluctor ring is all built into it

shortbus= said:

Yes there are different types. After chasing and trying to fix a couple of different GM cars with this type of fault, by changing to new wheel sensors then replacing the connecting wire harnesses, I gave up. And just made sure the brakes were functioning and ignoring the light.

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You can't do that in the UK, as an ABS warning light is an MOT fail - so the car can't be driven on UK roads.

I did provide a friend (who was a car mechanic) a resistor once so he could fit it temporarily to pass the MOT test, he then removed it so the light came back on.

I do think ABS should be switchable (and reset every time you start the car), as in snowy conditions ABS makes the car far more unsafe than not having it - car instruction books even warn you of this.

Hi Nigel

I’m in the UK, so I know exactly what you mean about the ABS light being an MOT fail, that’s why I need to get it sorted.
The stupid thing is all of this has only come about since replacing the front struts.

It looks like I will have to purchase an OBD2 meter to see if I can clear the warning light/codes, failing that I’m faced with taking it to garage to see if they can clear them.
Not to do any work, but just to see if they can be cleared, which means I will have to stick the existing sensors back in, and what a pain they were to get out in the first place.

All this technology, a fault code flags up and whatever is wrong is but right but the fault still shows.

I know some main agents charge about £100 just to stick a code reader on the car.

I’m trying sort out which code reader would be the best to go for, there’s an absolute shed load of different ones out there, I don’t want to go above £60, and looking at some code readers they don’t cover ABS.

If anyone reading this can suggest a suitable one, please let me know, in the meantime I will have to carry on trawling through the different ones advertised.

clive2016 said:

Hi Nigel

I’m in the UK, so I know exactly what you mean about the ABS light being an MOT fail, that’s why I need to get it sorted.
The stupid thing is all of this has only come about since replacing the front struts.

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Sorry, but it looks like you've done something to cause the issue - if you're lucky it 'might' just require resetting via a suitable OBD2 device.

Aren't there any VW forums out there?, I would expect such an issue to be commonplace is simply unplugging them causes this.

I was talking to a guy a few years back, who was servicing the handbrake on his VW - I was delivering something to him, and stopped to talk to him. So he mentioned the handbrake was electronic, so I asked him how it worked - I was staggered by the explanation - but on the bright side no one could steal his car, as they wouldn't be able to drive it

Many OBD2 readers only read codes related to engine problems.. When I had a sensor fail on my Toyota Avensis the ODB2 reader did not show up the fault but I found a tip online that suggested linking two pins on the OBD2 connector which gave a flashing error code on the ABS light. This took me straight to the failed sensor on which the coil had gone open circuit.. I bought a replacement Bosch sensor from a motor factors which cost about £65.00..

Les.

Being able to clear the ABS code for some reason makes it a more expensive scanner.

I have an Innova and it has upgradable firmware. It's a little more than read and reset codes/

We have places in the US where you can "borrow" tools for a deposit or get a free code read.

In ,my experience, ABS faults lights will clear in normal use if the sensor is repaired.

If one wheel is showing a very different resistance to the others, just change it.

The yellow light on the dashboard has done its job. It has pointed you in the general direction of the ABS sensors. A fault reader would tell you which one, but you've found that with a multimeter and a bit more time.

ABS fault light generally have to reset themselves, because they will come on if there is a big difference in wheel speed. When I had my car on a ramp and in gear, the ABS light came on because the front wheels were going quite fast (~30 mph) but the back wheels weren't moving. The light went off as soon as I drove the car normally above about 30 mph.

I also had an intermittent wiring fault on an earlier ABS car. The fault light would turn off when I turned the ignition off and back on, but the fault light would be back on when the fault recurred. When I had fixed the bad connection, the light stayed off.

If the ABS light were to stay on as soon as one wheel didn't send a signal back, you would only need to have a skid and then the car would have to go back to the dealers. I know ABS should stop a skid, but there are plenty of conditions like icy roads that could still cause a skid. Also, if a car is driving and getting four similar speed signals from the four sensors, it has proved that the sensors are working correctly, so there isn't much point in keeping the fault light on.

clive2016 said:

It looks like I will have to purchase an OBD2 meter

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Just get a _good_ OBDII interface, either serial or bluetooth / wifi. You can then use such as "Torque" on an android phone or tablet (with a bluetooth unit) or any of several free scanner programs on a laptop with a serial port unit.

I have an OBDLink MX interface, bluetooth connected, which works with Torque on android or apps such as Forscan on my laptop.

Torque will both display fault codes and reset them. Other programs/apps can do far more.

KeepitSimpleStupid

We have places in the US where you can "borrow" tools for a deposit or get a free code read.

In the UK we are blessed with only being able to hire building equipment and gardening machinery, sadly when it comes to cars, I’ve not found anywhere which hires out things like code readers.

Driver300

When you say ABS fault lights will clear in normal use if the sensor is repaired.

I don’t know so I’m asking, would this be the case with all warning lights?

I thought they had to be cleared or am I getting mixed up with fault codes?

clive2016 said:

Driver300

When you say ABS fault lights will clear in normal use if the sensor is repaired.

I don’t know so I’m asking, would this be the case with all warning lights?

I thought they had to be cleared or am I getting mixed up with fault codes?

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A warning light that doesn't have an obvious cause (so not door open, handbrake on, lights on, low fuel, ice outside etc) will usually have a fault code so that the technicians can work out what is wrong.

Some fault codes will clear on their own after some conditions have been met. Some will need clearing. There can be fault codes without warning lights. Once the fault code is cleared, the warning light will go out.

The conditions for fault codes to be turned on will vary. A lot of engine fault codes need the engine to be at full temperature before they will come on, and similarly there may be a number of drive cycles that get to the correct temperature to clear the fault code, if it can be cleared.

My current car has a particulate filter with a differential pressure sensor across the the filter. That is connected via long silicone rubber pipes, and they were burned out when I bought the car. The warning light could be turned off with the routine that clears the service indicator. The light would only come on if the engine was started when warm, and I didn't notice before buying the car. The point that I am making is that many signal values will only be considered faults under certain conditions, and a fault code will only be raised if the value is wrong, and the conditions are met. That one would only come on if the fault was present, and the engine was started when warm.

The final outcome of the ABS saga.

Driver300 has got it somewhere near right, when I was working on the car it was on axle stands all round and I had the issue of the ABS light staying on instead of going out after the ignition had been on for a few seconds.

I still can’t understand why as I didn’t have it in gear with wheels turning, I did try it with engine running but in neutral, but it made no difference.

Anyway, I decided to take it to a garage and have it tested to at least find out which wheel was giving the trouble.

I started to drive to the garage and didn’t the ABS light go out, I stopped the car turned the ignition back on without starting the car and ABS light went out after a few seconds so whatever it was seems to have righted itself, but if someone asked me what it was that kept the light on, in all honesty I haven’t a clue.

Thank you fellas for all your replies they were much appreciated, in the near future I may decide to get an OBD2 scanner but the ones capable of reading ABS codes I think are at least £160 here in the UK.

clive2016 said:

in the near future I may decide to get an OBD2 scanner but the ones capable of reading ABS codes I think are at least £160 here in the UK.

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Way cheaper - a VW compatible interface 49 euro, basic software 10 euro or 30 euro for the dedicated VW basic software, which is all you should need. The more expensive one looks to allow for reprogramming stuff. [Get the CAN version software, if you go for this].

There may well be other free software that works with that interface; and likely other interfaces - the one I have may well work, but is more expensive than that wired one.

Driver300

Thanks for the lowdown on the codes and warning lights, it’s very informative.

Rjenkinsgb

Thanks for the info about scanners, a scanner which would be far more useful to me isn’t for a VW Golf MK5 but for an old Isuzu Trooper 3.0 TD year 2000 which I use for towing, I believe they are also used on GM motors, I’m assuming Vauxhalls.

What I’ve tended to see referred to in the Isuzu Workshop Manual, is a Tech 2 scanner again they are in the region of £260.

Do you have any ideas on a cheaper way of getting a scanner or program for that vehicle?