AUDI A4 ABS light after brake disk and wheel bearing replacement
 

Audi A4 1.8Ts 1999 (B5), front wheel drive, Avant.

My problem is the ABS light glowing and the bigger display showing the red brake fault sign followed by 3 loud beeps.

This started directly after I had replaced my rear right brake disk and wheel bearing (wheel bearing integrated in brake disk). Sometimes the light goes away while driving but after braking hard a few times it comes back.

I checked with a VAG-COM for fault codes and found one under "ABS/Brakes":

Fault code: 00287 - ABS Wheel Speed Sensor; Rear Right (G44)
35-10 - - - Intermittent

In my VAG program I also monitored all wheel speed sensors while driving around below 20 kmh on my parking lot: Heres the graph: (Gray = rear right)
Attachment 64878

As you can see, rear right sensor has no output below ~10 kmh but above it glitches.

During the replacement I brushed off some dust and metal chips on the ABS sensor and some rust around its socket with my wire brush. There were alot of rust around the sensor.

I reused the old ABS sensor ring which I brushed off with my wire brush (just dust no flakes) but was a bit less careful on this side (did same job left side day before) when punching the old sensor ring on the new disk: (the piece between the ring and my hammer is a fallen off piece from an old spring)
Attachment 64879

After punching it on I noticed I had damaged one tooth just a tiny bit (<1mm), looked really tiny so didnt think it would cause any errors (no picture sadly) so I mounted everything back on.

Whats making me wonder what could be the error is that I did get SOME information while monitoring the wheels.

I dont think there is an electrical fault because I didnt touch the backside of the shield at all except when loosening the caliper, what I think could be the error is either somehow the disc are too far away from the sensor (maybe when brushing round the sensor and the rust flew away it moved a little bit) or obviously the damage I caused to the ring was enough for this to happen.

Check and make sure the sensor isn't adjustable (depth-wise) in the hole. Some of the older ones are and if you remove them or the ring, you have to reset the sensor to the proper distance. The older ones have a plastic cap on the ends that touches the ring when installing. It retracts slightly when activated, setting the proper distance from the sensor to the ring. I've not played with the newer ABS setups on these things. Not had to. Yet.. LOL

How can I see if the sensor is adjustable? It lookes likes solid metal.

Then it's probably not adjustable. The older ones were kind of like crank reference sensors that slipped into a hole in the spindle assembly but bracket that the bolt that held them in was slotted so you could set the depth. Looking at yours in the parts catalog, they look similar but the bolt straight in. I'd try a new sensor since they are only about $70.

Hahah, I solved my issue, it was the wheel bearings being too loose, I tightened the wheel bearings and now the ABS light is off and it seems to work.

Glad it was something simple. I hope the looseness of the bolt didn't cause any damage to the bearing though. If it starts roaring after a while, you'll know it did.