ABS Engaging at Low Speeds

[DSM 2 Avant]

I've bee trying to troubleshoot my ABS for some time now. It will activate at speeds between 5-10mph. It always kicks in the front driver's side wheel.
So far, I have rebuilt the ABS module, changed the driver's side ABS sensor and the CV joint for the tone ring.

I've searched and everyone has been able to fix it with a new speed sensor. Wish I could say the same.

Any ideas what else it might be? The only thing left to replace will be the wheel bearing. It doesn't hum or anything so I'm not too confident this will solve my problem.

[Just Quaff]

How you know its engaging? Is the light just flashing up on your display?

[DSM 2 Avant]

I can hear and feel the front driver's side brake pulsating The ABS light doesnt come on though.

[Just Quaff]

Sounds like your rotors are just warped. Pick up some new ones :) Slotted/Dimpled FTW!

[Rhinop21]

I used to have this, it sounds like clink clink clunk. Mine was always at 15mph so i just disconnecting the abs module, now i have a light and no abs. but no clunkity clunk

[urban96]

I've bee trying to troubleshoot my ABS for some time now. It will activate at speeds between 5-10mph. It always kicks in the front driver's side wheel.
So far, I have rebuilt the ABS module, changed the driver's side ABS sensor and the CV joint for the tone ring.

I've searched and everyone has been able to fix it with a new speed sensor. Wish I could say the same.

Any ideas what else it might be? The only thing left to replace will be the wheel bearing. It doesn't hum or anything so I'm not too confident this will solve my problem.

have you tried unplugging it and seeing what happens?

[MattzWarsteiner]

Somethings up with the control module or the sensor I would guess. On my car the control unit is under the rear seat. The output module is the one on the hydraulic block under the hood and if it fires at the wrong time, there should be a trouble code and ABS telltale light.

Have you tried running VAG COM in log mode ? Record the measuring blocks for the wheel speed sensors and there might be a clue here, like maybe that sensor is sending bad data to the module because of bad wiring or broken reluctor ring.

I'm not sure how safe this would be to try and you should not drive the car far in this condition but what about swapping front left and right sensor connections at the module. You may have to rig up a temporary harness connector to do this. If the problem switches sides, you can focus on the sensor, reluctor and wiring to correct it otherwise it would point to the control module being flaky.

[mike-2ptzero]

have you tried unplugging it and seeing what happens?

Thats the first thing I would do, this will rule out if it is actually the ABS that is causing the problem.

[DSM 2 Avant]

When I removed the output module (the one on the hydraulic block under the hood) to have rebuilt the problem went away.

I also ran VAG com before I had the unit rebuilt and noticed that the driver's side speed reading was off compared to the other wheels. This is what made me get the speed sensor and CV joint replaced.

The old sensor had a few rub marks and the tone ring had a some damaged gears. So I'm thinking play in the bearing is causing erratic readings. I have over 112k miles on it anyways. So it won't hurt to change it.

As MattzWarsteiner mentioned, it could also be the control module under the rear seat.
Does anyone know how to test it?

Thanks for all the responses so far, everyone!

[cray54]

I'm having the same problem on my front passenger side. I'm anxious to hear how this works out..

-Chris

[AudiRacerS4]

probably a wheel speed sensor

[albertnkansa]

I just developed that problem yesterday.. it started after I changed the right axle and all the control arms. Abs engages at between 5-10mph.. at some point the abs and hand brake light come on.... its a 1996 audi a4 fwd.. another thing is that I parked the car for 4 moths without driving it.. and the radio went dead in me during that time.. any clues as to what to do

[MattzWarsteiner]

I would check the wiring and connector thoroughly and then try cleaning and adjusting the sensor height by moving in or out of the bore. If nothing helps here, try cleaning the reluctor ring with some brake cleaner and shop air if you have it.

If the battery was dead when you got back, you need the radio code. Supposed to be with the owners manual on a page or strip of paper. Dealer can tell you but might charge you especially if they have to pull the radio out to get the serial. Search for radio code here to find out how with your type.

[quattro16]

Usually this is all from a cracked tone ring on one of the 4 joints. Use to happen alot and Audi came out with a TSB for all cars. Its really old though. I would say to loosen all axle bolts and push the axles out alittle and inspect all tone rings for cracks. Its very hard to tell so keep a good eye!

[tamadrumr88]

hmm, mine does it only if i get on the brakes rolling backwards out of the driveway immediately following startup

[ic3wall]

I have the same problem ...so annoying!

these ****ing speed sensors are quite expensive and are also very difficult to take out..

[messepants]

I had the same problem I just pulled the sensors out and cleaned off the ends and the problem went away. The sensors are hard to get out but they do come out.

[rdguy]

I have the same problem on my 98.5 A4 quattro. I did a vag test and all wheel were at the same speed up until I tried to remove a wheel sensor. Now one wheel has an "open to short" failure message and it does not read on a vag test.

I can replace the sensor but I assume I will go back to pulsations. Right now the ABS light is on and I have no ABS.

What is the best way to remove the sensor? Vise grips on the metal side of it?

[onepoint8tee]

Dealing with the same thing. A bad brake light switch can cause this. If you have vag com, go into the brakes control module, go to block 2. Slowly press the brake pedal, if you see the value for voltage to abs occur before or at the same time as you see a value for brake light switch change, you have a bad brake light switch. If the toner rings arent broken or gunked up, try this. The sensors don't normaly break, they are just a magnent that can get dirty. Try cleaning them. To keep your abs from activating in the meantime, just diconnect your abs control module under the hood. Find a box end wrench that fits around the base of the sensor snugly, and twist back and forth while pulling. Vice grips might work too, but be careful.. The wheel speed sensors are at least $150.
I would get a skinny fine wire bush and brake cleaner and go to town on the sensors.

hmm, mine does it only if i get on the brakes rolling backwards out of the driveway immediately following startup

Thats just the ABS cycling (self check) it does this after every startup.

[rdguy]

UPDATE on my Sensor!!!

I managed to get the sensor out tonight. Took a while since it was seized in pretty good and destroyed it getting it out. Had to chisel out the metal sleeve with a screwdriver and awl and then the outer sleeve came out pretty easily.

BTW, this sensor was working fine before I messed with it. I tried to get it out to check for dirt or contamination being the possible cause. I vagged it before and all wheels were at the same speed, then vagged it after I broke the connetion and the one wheel did not read while the other 3 did. I am going to assume the Bosch 5.3 module is the culprit but I will replace the sensor first.

Now that that is out I need to buy a new sensor. Has anyone tried the one on Ebaymotors for $75.00 ? Is it compatable with the other 3 vdo sensors on the car?

[DSM 2 Avant]

Thanks all for keeping this thread alive. I'm still dealing with my ABS issue. I'll have to try block 2 in the Vag.

rdguy-Let us know if you replace the Bosch module

[rdguy]

Surfing around last night I also found information to test each wheel sensor with a multimeter. ModuleMaster.com had the test proceedure.

[A4Gasm]

Same thing happened to me today, except issue starts at 20mph and ends at 10mph. My previous ABS module had been broken for almost 2 years. I just had a new one installed last night, and all of a sudden, I get that noise(almost sounds like rotors scraping) and the feeling in the brake pedal(crunch crunch crunch in 1 sec intervals).

Here's what the module masters tech guy told me.

This is not verbadum, and I probably mixed terms up, but hopefully this gets some of us noobs such as myself on the right track.

*Go to large connector on the module, Using a multimeter, measure the connector of the wheel speed sensors as you rotate the wheel - Should see 200 ac milivolts. If one reads less or more, then the sensor may be faulty.
PIN Location on connector:
Right Rear = Pin 1 and 2
Right Front = 4 and 5
Left Rear = 8 and 9
Left Front = 6 and 7
Sensor generates voltage to the module. At this point, it may thnk the tire is locked up, thus creating an unusual amount of voltage which manifests itself as the feeling in the break pedal.
Sensors should be located in the back of the hub assembly. Could have become dirty in the 2 years with out ABS*

[rdguy]

It has been a while now and I have replaced my front sensor. I also had the module checked and it is fine. I guess I need to measure the wheel sensors now.

[Toyotatech]

On Toyotas we have had this problem from time to time and how I fix it is I do a linear valve calibration of the abs pump. I don't have vag-com so I can't tell you if it is possible on an Audi.

[Rhinop21]

On Toyotas we have had this problem from time to time and how I fix it is I do a linear valve calibration of the abs pump. I don't have vag-com so I can't tell you if it is possible on an Audi.

Then don't post, im not trying to be rude but that might throw some people off. To whoever, get vagcom and see which wheel your dealing with. Clean the wheel speed sensor and go from there. I didn't have abs for the longest time because I thought it was a bad module. I cleaned all my wheel speed sensors and poof no more problem. Mine was the right rear it had dirt in the sensor that interfered with the magnet on the sensor.

[Toyotatech]

Then don't post, im not trying to be rude but that might throw some people off. To whoever, get vagcom and see which wheel your dealing with. Clean the wheel speed sensor and go from there. I didn't have abs for the longest time because I thought it was a bad module. I cleaned all my wheel speed sensors and poof no more problem. Mine was the right rear it had dirt in the sensor that interfered with the magnet on the sensor.

Sounds to me like you don't have enough knowledge to solve your own car problems, the difference between a bad module and a bad/dirty sensor are obvious. I gave information on how to fix it on a Toyota since I don't have vag-com I am unable to tell you whether it is possible to do on vag-com but it is something maybe people should try looking for. The linear valve adjustment is a self calibrating procedure done through Toyotas Techstream system, so simple even you could do it if someone told you that's what it needed and where to find it.

You may not be trying to be rude but you are. Some people say they are still having problems and your fix isn't working, your diag skills don't sound too great either.

[rdguy]

I have pulled the big connector harness but I don't see pin locations marked?
Do you know which pins to test , Diagram maybe???

Rick

[stdriver]

I just had this problem, I unplugged the cord going into the module and it went away when i drive it. so it has to be one of 4 abs sensors or the module im guessing?

[jcs98audi]

I had this problem.. Got my ABS module re-done at modulemasters.com.. put it in.. had the pulsating ABS at like 3 mph when coming to a stop.. I knew I needed new front pads and calipers.. so I did that, while I was in there I cleaned off both sensors with a clean rag and brake cleaner and used my air compressor to blow out the female side of the ABS sensor.. no problems what so-ever! Brakes like a champ and no ABS kicking in unless flooring the brake pedal (normal)

FYI: for those who unplug your ABS module.. there goes your AWD! If you have a bad module get it fixed, that provides your traction control too.. so you my as well be a front trak.. and if thats the case whats the point in having an audi with the world famous quattro drive train??? just saying..

[Loafy03]

FYI: for those who unplug your ABS module.. there goes your AWD! If you have a bad module get it fixed, that provides your traction control too.. so you my as well be a front trak.. and if thats the case whats the point in having an audi with the world famous quattro drive train??? just saying..

Not entirely true. You'd still be running with AWD however you lose the side-to-side torque distibution achieved through the brake system. If, on a given axle, one side loses traction, that wheel has brakes applied through the ABS system in order to distribute the power to the other wheel since we're working with an open differential on our front / rear axles. Even with no ABS, you still get the static 50/50 front/rear split through the mechanical (not electronic!) torsen center diff.