Audi 80 b4 quattro abs problem

[Froggzy]

Hi,

My b4 quattro have had this abs issue for a while. The abs kicks in when braking at slow speeds (10-0km/t). I have checked all four sensors and rings. One faulty sensor was replaced and all rings looked good and was cleaned. I also changed out all the brake fluid (bleeding half a litre to one litre per brake to be sure.

I am out of idea where to search for errors without replacing the pump and abs ecu..

Any more tips and tricks would be appreciated! I've also tapped all sensors with a hammer to ensure that they are all the way in.

-Froggzy

[sam80quattro]

You need to pull them back out a bit.. There needs to be a small gap

[chiefmechanic]

Tap the sensors in while you spin the wheel by hand. If they start to rub then back them off a bit. Needs only a small gap.

[LYT4X]

The problem is definately to do with the sensor gap. Don't waste time/money chasing faults with the pump/ECU.

[Froggzy]

Hmm.. will try to pull them back out a bit when I get home from offshore. Thanks for the answers, will write back when I have tested this

[ManiacuV6]

Or is you have enough space you can use a feeler gauge to measure the gap between trigger wheel and sensor. You need to have the same gap.

[Froggzy]

Now i have changed the whole abs pump unit, abs ecu, all four sensors and rotors, and all relays, any idea anyone? Still same problem.. did ofc bleed all brakes for ages, starting at the rear right side.

[Froggzy]

Some thinking got me to this. The abs should turn off when you brake below 10 km/h, shouldnt it? Like, if you slam the brakes, you got abs but the last ~10 km/h to stop, it locks the wheels? Mine does the exact opposite no matter how careful i brake. Could it be a wire between the ecu and pump, that tells the abs to shut off during 10-0 km/h braking, that have snaped, so the abs does the opposite?

Hard to explain, but i think all the sensors and rotors etc works fine, since the abs works like normal above 10 km/h. Am I way off or does this sound correct?

[ManiacuV6]

if the distance between sensor and trigger wheel is not the same ON ALL WHEELS then your problem.

[Froggzy]

The gap is the same on all sensors. 0.30 mm on all four wheels. The abs works as it should above 10 km/h so i dont think its the sensors, it has to be with the function that blocks the wheels from 10-0 km/h imo.

Edit: all sensors gives the same resistance and creates about the same voltage when you rotate the wheel.

[RichLV]

Check if the ABS rings on CV joints are clean and not rusted. Had exactly the same problem. Turned out front left ring was rusty and corrupting the speed reading. Cleaned it and it went away.

[Froggzy]

Alle the rotors are brand new.

[Tom_]

Hello Froggzy, are you solved this problem yet?

[Froggzy]

Yes, found out that one sensor was a little further out than the others, by measuring the voltage again (i measured wrong). Soaked it in wd40 and worked it till it came loose, managed to knock it a bit further in and the problem was gone

Now i have bought an s4 b5, that has the exact same issue ��

[Tom_]

Measured wrong?How? I measured today a resistance

Front right (driver) 1.186
Front left 1.198
Rear right(driver) 1.128
Rear left 1.172


than a measure a voltage with turning wheels...almost ale wheels had the same numbers (0,30 -0,50 depends on speed) but almost the same problem as you. Today a few people told me, thats its good to knock sensor to the max, tomorrow i go for new sensor, because the old one was a little bit damaged after i remove it from hub