OrangeMan

I've had a lot of trouble on my car with regard to the ABS system and any insight or help would be greatly appreciated.

I purchased the car (2000 A6 2.7t tip, 125k miles, now has 153k) in September of 2009 with the ABS light on. After replacing a wheel speed sensor (RR) the ABS worked fine until February of 2010, when the ABS module died. I didn't really care and didn't really want to bother fixing it until this winter when the brake light and three beeps on start up started driving me crazy. In February of 2011 I pulled the ABS module and paid $100 to send it to Virginia and have it be re-soldered.

When I got it back the ABS light was still on but the flashing brake light and three beeps had stopped. I had it diagnosed as another wheel speed sensor on the front right corner.

I replaced the RF Wheel speed sensor and got the car back. Everything was fine. However less than 24 hours later, the ABS light came back on and the car would not kick on the ABS no matter what. I had to drive the car around for about 2 weeks before I could take it into a shop or take a look at it myself. During this time, the car would occasionally and randomly have ABS when I went to brake, and it would be incredibly over boosted, the pedal would start pulsating at the slightest press, like when coasting down to a stop sign or canceling the cruise control on the highway. So at this point the ABS light is constantly on 99.99% of the time and the ABS system is not functioning at all, except for those few times once every other day or so.

I brought the car back into the shop in Syracuse where I had had the speed sensors replaced. They told me everything looked good, so the took apart the RF hub and said that the counter ring on the end of the half shaft was badly rusted and that that was causing the problem. Then they quoted me $450 to replace it (I immediately went online and found a half shaft on bimmerparts.com for $99 and called the shop, they told me they would install it for $120). They also told me they did nothing to the car other than take the hub apart to look at the half shaft, and then put it back together.

I went and picked up the car Friday. Now the ABS light is off all the time, and every single time I decelerate to a stop, the ABS kicks in and the brake pedal starts pulsating from exactly 10mph to 6-7 mph, then the car stops fine. It does this every single time, no matter how hard or soft you are on the pedal.

I don't even care about the damn ABS system, I like the car better without it, especially in the winter. I just hate having lights on in the dash and am trying to sort it out to sell. Now I feel I have to fix the system just to sell the car. I am really sick of spending money on this; I just keep thinking I am one fix away from the system working fine so I go for it. My questions are these:

1. Do you guys really think a rusted counter ring on the half shaft is the problem? I understand how the counter ring and speed sensor system work; I just don't understand how the ring could be the problem at an exact speed every time. It seems to me like if part of the ring was messed up/rusted/damaged, it would be an issue at every speed. Since the sensor is measuring the distance or time between the points on the ring and running them through algorithms to determine if the wheel is slipping or sliding or a whole number of things, wouldn't a defective ring show up at any speed?

2. Is there a fuse I can just pull that disables the ABS system without unplugging the ABS module (and thus tripping the red brake light flashing and three beeps on start up?).

3. If I do replace the half shaft what are the bolts that connect the shaft to the CV joint on the inside of the car? They are slightly larger than a Torx 50, but have 12 points instead of 6 like a torx.

4. Do I have to remove/mess with any of the suspension in order to remove the half shaft and install a new one? I pulled a wheel off today to look but I wasn't really sure what I would need to do after I took the hub apart and got the brake rotor and caliber out of the way?

Thank you very much in advance for your help.

jseklund

Never replaced the rear half shafts, but have done the fronts a couple of times - not a bad job on the front at least. The bolts are triple-square bolts, you can get them at autozone, advance auto, or Big A. Cost about $15 for a set.

Do you have a vag-com tool? If you do, you can monitor the wheel speed sensors while you drive the car around in a parking lot. They should all read the same. What's interesting, if I remember correctly, is that I think you can only monitor the wheel speed sensors up to either 10 or 15 mph. Then the system doesn't work the same I think, and the computer won't allow you to monitor above this speed.

To me, it sounds like a bad wheel speed sensor and classic audi dealership syndrome. Oh, yeah, we replaced that, it's fine. But it wasn't the right sensor, they broke it when they put it in, you name it.

I think monitoring with the vag-com while driving 5-15 mph, taking turns, etc. will give you more insight.

Also, sometimes you can CAREFULLY remove the sensor, clean it and replace it and it works again. They often get gunked up and malfunction....

Good luck.

OrangeMan

Thanks, don't have a VAG COM just a regular OBD II software program. It can do a zillion things but wheel speed is not one

4Driver4

Diagnostically, you are out of luck without VAG-COM. Time to buy it. It probably is a broken or damaged tone ring.

mpower99

Check for cracked tone ring on the rear axles.. Very common issue. The cracked/broken ABS ring symptoms are exactly what you describe. The rear axle rings are a lot more prone to failure.