ABS keeps cutting in - any ideas?

[avantman]

Hi
My car has this annoying problem that when braking I can feel the ABS cutting in while slowing down. It happens very frequently and can be even at low speeds and on decent road surface in dry conditions - any ideas?? Is this an early sign of a sensor/controller problem?

 

[docurley]

If you have changed the pads recently they may be dirty or not seated correctly.

 

[avantman]

I put new discs and pads on recently but the car had the ABS issue on the old setup before I changed everything over. All parts I have used to date have been original Audi parts.

 

[jonS3]

could be air in the brake fluid, I had this happen on my S3

 

[avantman]

this may be a silly question then, but what normally happens when an ABS sensor fails - do you get warning lights on the display turn on or other telltale characteristics?

 

[marms]

Also think it is quite common for too much copper grease to be applied when changing pads. This excess can contaminate the sensors and cause problems. It is for this reason that Audi recommend not using copper grease.

First thing I'd try is cleaning the sensors.

 

[docurley]

this may be a silly question then, but what normally happens when an ABS sensor fails - do you get warning lights on the display turn on or other telltale characteristics?

The Abs would stop working and you would only have stock brakes without the ABS.

I would go with my first option and clean them.

 

[avantman]

ok will do, am due to change spark plugs/filters within 500miles so will take a look

Cheers for the help guys!

 

[shineydave]

this is a common problem, i know of at least two other S4's that have it. one of them was cured by pulling the sensor away from the sensor ring on the offending wheel. the other one is still a mystery. it's been cleaned, had the sensors pulled out and sensors pushed in but still exhibits it.

another common reason is that the sensor ring has cracked causing a false signal.

and to cap it all you can't trace this fault accurately with Vag-Com as it disconnects from the ABS ECU as soon as you get moving.

sorry i can't be more help

 

[avantman]

Thanks for the advice. Is there any way to narrow down the possible options i.e. determine which sensor on which wheel could be the offender? I have a laptop/cable/vag.com but don't know where to start...
Cheers

 

[Turbo Lag FTW]

Or it could be a wheel bearing, seriously I had same problem with my ABS after changing front discs and pads. Bought a new sensor for drivers side as it looked in a bad way, nothing happened, still the same ABS cutting off over 55mph.
Took it to garage they removed and cleaned all sensors, stopped going off for all of two days and problem came back with a vengeance, so anyway 2 weeks later had MOT done. With having the problem I thought it was gonna fail but the inspector found that the rear passenger wheel bearing wasnt in good shape so he changed it, he then tested car for brakes and it passed with flying colours. So I asked him if brakes were ok and he said they spot on, and I told him the ABS wasnt working before I took it in, he took car out for test drive and said it was A O.K
Never had problem since, goes to show that anything can cause ABS problems

 

[Markey]

I think vag-com could possibly tell you where the problem is i have never used it yet to check the ABS, i had this problem on my other A4 and it was a bent ABS ring on one of the rear wheels which kept causein the ABS to cut in when ever the brakes were pressed.

 

[shineydave]

vag-com can tell you if there's a permanent fault but this one isn't a fault as such, it seems that it's not a sensor that's faulty but rather something else that's mis-aligned (wheel bearing or sensor) or broken (sensor ring) the abs is detecting a mis-match in wheel speed because of something not tip top and so operates the abs for that wheel, as such it's working correctly.

now the best way to check using vag-com would be to connect to the abs controller and monitor each wheel in turn and see what readings you're getting, unfortunately vag-com disconnects from the controller as soon as you start moving so you can't use it to fault find this problem.

hope that makes sense

 

[Turbo Lag FTW]

yeh like shiney says it could be a mis-alignment of the ring that causes the ABS to switch off, was in my case. So many variables that can cause this problem and thus is a nightmare.

 

[andybnwc]

Yep had the same problem sensor was it too far pulled it out a bit and all was ok