ABS faults, any way to test?

[mcandmar]

Since i had the rear end apart i've managed to break my ABS, lights stays on all the time now. I had both rear sensors removed when changing wheel bearings so it has to be one of the two.

Question is how do i test the sensors to find which is at fault? And does the sensor have to be mounted in the hub for the ABS system to pass its self test? i.e. if i get a spare sensor and only plug the cable in will the ABS light go out?

I just cant figure out if the electronics are toast or if i havent got them mounted properly

Thanks,

Mark.

[hybridavant]

Hi mark this is a common problem seen it loads of times after suspension work.
Best thing to do is first make sure both sensors are fully pushed home (i assume they are free to move in the hub?).
If that fails check the resistances (meter set to ohms) accross the conector pins to the sensors with a multimeter,compare the readings with known good sensors (front in your case) ,if one of the readings is a lot higher or lower then thats your prob.
Sometimes when you remove the sensors by twisting the top part moves and the part in the hub stays put,this can damage the internals ,as can shocks from hammers near the sensors.
Good luck

Since i had the rear end apart i've managed to break my ABS, lights stays on all the time now. I had both rear sensors removed when changing wheel bearings so it has to be one of the two.

Question is how do i test the sensors to find which is at fault? And does the sensor have to be mounted in the hub for the ABS system to pass its self test? i.e. if i get a spare sensor and only plug the cable in will the ABS light go out?

I just cant figure out if the electronics are toast or if i havent got them mounted properly

Thanks,

Mark.

[mcandmar]

I have taken them out since and refitted them so they should be mounted ok. I'll check the resistance and see what there like. Should i see the signal fluctuate if i rotate the hub or do they need power to work?

Thanks,

Mark.

[hybridavant]

No you dont need to rotate the hub just check resistance static and compare with a good one

I have taken them out since and refitted them so they should be mounted ok. I'll check the resistance and see what there like. Should i see the signal fluctuate if i rotate the hub or do they need power to work?

Thanks,

Mark.

[topsparky]

won't vag com tell if they're not working properly

[martinjs]

Check the fuse under the dash first Mark, (cant remember the number but it sits in one of the relays, there is a thread about it somewhere) I had a similar problem, started messing about with the sensors but it was the fuse which was keeping the light on. doh!

[s2dude]

Check the fuse under the dash first Mark, (cant remember the number but it sits in one of the relays, there is a thread about it somewhere) I had a similar problem, started messing about with the sensors but it was the fuse which was keeping the light on. doh!

Fuse 31 - 10 amp iirc


Also.. Test the connectors under the seats and under the bonnet and measure the resistance between the two pins of the sensors. They should be about 1k ohms.
If either is way out..its duff

[s2dude]

Also....I think incorrectly positioned sensor can make the light come on.
What method did you use to reposition the ABS sensors in the hub?

Also, does your ABS totally not work now??

[mcandmar]

That’s for the help guys, its been raining all day long so i'll have a look over the weekend.

Vagcom won’t work with mine as i have the early ABS with an on/off button. For fitting i pushed them in as far as they would go until i hit some resistance, then rotated the hub to make sure they weren’t rubbing. I couldn’t see any way to be sure there in far enough, and didn’t want to damage them by forcing them in further with a hammer?

Didn’t know they connected under the rear seat, cheers for that. All i could see was the cable going up under the boot floor

Does anybody know if there same sensor is used on the front and back? There are a few on ebay but i cant get into my etka to check if there the same.

Cheers,

Mark.

[martinjs]

For fitting i pushed them in as far as they would go until i hit some resistance, then rotated the hub to make sure they weren’t rubbing. I couldn’t see any way to be sure there in far enough, and didn’t want to damage them by forcing them in further with a hammer?

Thats how i set mine, worked ok.

[CHEN]

Different sensors front and back, I think you can make them fit but the grommits are wrong and I cant remember which is longer

[S2central.net]

My recollection of this is that any faults stored in the ABS controller (such as detecting a faulty/open sensor) are that the fault must be cleared with VAGCOM - or by removing the fuse for a minute.

There is quite a lot you can do with ABS on 1992 onwards cars on VAGCOM but 7A and 3B engined Coupes have an older (less 'intelligent') controller which doesn't talk to VAGCOM - a specialised test device is needed for all tests.

Advice on location of the new sensors is good - so is the electrical check !

Paul

[s2dude]

Fitting method sounds fine! A gnats whisker out from being in contact with hub ring.

Though Im not sure why you would need to hammer the sensor in further? Im assuming the hub ABS holes were cleaned and the copper sleeves are in place? I had to buy new copper sleeves and to get a comfy fit used a round file carefully to remove any surface rust...
Sensor should be a snug push fit (by hand) and should also remove by hand...lots of copper slip in the copper ring I used to prevent seizing up in the future hopefully!

Also. Under rear seat into ABS ecu and fronts are located (on 3b anyway) ....1 is under the airbox which needs removing to get to it....the other is buried somehwere in region behind coolant tank iirc!!

Same sensor is used front and back however the ones at the back are longer than the fronts.....Also, most come with an incorrect connector (square)
After having to rebuild my complete ABS and I also did all hubs when I got my S2 I found this out! All you need to do is get any working sensor off ebay....measure to the correct length you need and cut your old sensor and use the plug end from that....and snip the new sensor at a suitable length and join the two together (soldered and heatshrink was the method I used).

Also.. check continuity in your old lead after you have cut it just to be sure its ok and before its mated to the "new" sensor