Abs Light On

[Pearly]

I have a 2005 Mk2 Galaxy. After doing a three point turn (full lock) my ABS dash light came on. At first it would go out after stopping / starting the car. Now it is on all the time.

 

I took the car to an independent garage that I always use and VAG-COM indicates a mechanical failure in the off-side ABS sensor. After checking and cleaning the sensor ring to no avail he replaced the sensor, this made no difference either.

 

Now he has changed the whole CV joint, guess what, same problem!!

 

He has checked the sensor wiring by detecting the sensor resistance and is now stumped.

 

He wants to take the car to Ford, this is going to be expensive...

 

Has anybody any idea what else this could be?

[serviceforce]

bad connection where abs sensor plugs in under wheel arch?

[sparky Paul]

If the problem occured after a bout of full lock, my guess would be wiring under the wheelarch too.

 

It's worth making a good visual inspection of the wiring, particularly around the socket in the wheelarch as serviceforce suggests. If the wiring insulation is split, the resistance of the sensor may still be measured at the ECM unit, however the signal could be being partially grounded to the car chassis. Make sure the wiring is checked carefully around the socket, particularly inside the rubber strain relief. NSF and OSF sensors can be interchanged to prove a faulty (or working) sensor.

 

This may seem a silly suggestion, but has the car been driven on the road since the work was done? An ABS fault will only clear itself when the car is driven over 20mph.

 

Also, is there any particular reason why the whole CV joint has been changed? The CV reluctor ring for the ABS is available separately and can be easily changed without swapping the complete CV joint. Another silly question, but are you certain that the replacement joint came with the ring fitted?

Edited December 30, 2010 by sparky Paul

[Pearly]

bad connection where abs sensor plugs in under wheel arch?

 

Thanks for the quick reply, I will ask the mechanic to check (if he hasn't already)...

[Pearly]

If the problem occured after a bout of full lock, my guess would be wiring under the wheelarch too.

 

It's worth making a good visual inspection of the wiring, particularly around the socket in the wheelarch as serviceforce suggests. If the wiring insulation is split, the resistance of the sensor may still be measured at the ECM unit, however the signal could be being partially grounded to the car chassis. Make sure the wiring is checked carefully around the socket, particularly inside the rubber strain relief. NSF and OSF sensors can be interchanged to prove a faulty (or working) sensor.

 

This may seem a silly suggestion, but has the car been driven on the road since the work was done? An ABS fault will only clear itself when the car is driven over 20mph.

 

Also, is there any particular reason why the whole CV joint has been changed? The CV reluctor ring for the ABS is available separately and can be easily changed without swapping the complete CV joint. Another silly question, but are you certain that the replacement joint came with the ring fitted?

 

Again, thanks for the quick reply. The car has been driven for weeks since the work was carried-out, the snow prevented me taking the car back sooner. I already saw mention of a 20mph drive required to reset the fault indication.

 

The mechanic told me he could only order a complete unit, he couldn't get the sensor ring on it's own so I would presume he checked the replacement came with one fitted otherwise he wouldn't have mentioned it. I know you can now get the sensor ring separately after reading these forums, but I suppose it depends on his supplier. I will pass all this information on, personally I don't see what else Ford could do except charge me a lot more money...

 

One question though, would VAG-COM still report a mechanical ABS sensor error if it was the sensor wiring?

 

Can he swap the plugs at the ECU to swap over the NSF and OSF sensors or do you mean physically remove the sensors and swap them?

[sparky Paul]

One question though, would VAG-COM still report a mechanical ABS sensor error if it was the sensor wiring?

 

Can he swap the plugs at the ECU to swap over the NSF and OSF sensors or do you mean physically remove the sensors and swap them?

 

The errors logged can be highly specific, but on occasions can be misleading and faulty wiring can produce unexpected faults... it is worth checking the wiring. It might also be worth comparing the airgap between the sensor and the reluctor ring on the NSF and OSF, to make sure they are similar, to confirm that the new parts are correct, and correctly fitted.

 

Physically swapping the sensor left to right will prove that the new sensor pickup is functioning correctly. I almost suggested swapping the connections at the ECU but I'm not sure if it's possible. If it is, it would certainly give you some very helpful info... failure of the Ate-Teves ABS ECU are certainly not unheard of in VW circles. Main symptoms of ECU failure seem to be sensor faults, 'pump out of tolerance' fault, and erratic speedo.

Edited December 31, 2010 by sparky Paul

[zorgman]

i would go for broken wire if not the reluctance sensor may nee moving in nearer to the ring, now my light comes on but abs still works a i found out while playing in snow, be carefull with the sensors as they sieze in and 9/10 times you have to destroy them to get out, also the connector can go high impedance may be worth trying to give good clean

[Pearly]

I finally took the car back to my mechanic and he has checked all the wiring and the connector and found no problem. He thinks it may be the ABS ECU. Because he only has a handheld VAG-COM unit he has asked me to take the car to Ford as they apparantly can run a better diagnostic and can simulate the sensors to the ABS ECU. This should prove whether the ABS ECU is faulty before I replace it.

 

Anybody any idea how much a new ABS ECU is likely to be?

 

I have seen one on eBay from a breaker with the ABS pump for about

[Pearly]

I am reposting this because I did it just before the site went down, so maybe notifications etc didn't work...

 

I finally took the car back to my mechanic and he has checked all the wiring and the connector and found no problem. He thinks it may be the ABS ECU. Because he only has a handheld VAG-COM unit he has asked me to take the car to Ford as they apparantly can run a better diagnostic and can simulate the sensors to the ABS ECU. This should prove whether the ABS ECU is faulty before I replace it.

 

Anybody any idea how much a new ABS ECU is likely to be?

 

I have seen one on eBay from a breaker with the ABS pump for about