ABS/Brake Warning Lights Only When Using AC

[Dommi3]

Here's a weird one.

My ABS/Brake light lit up on the dash so I assumed it was a bad sensor like in the past. Also that's exactly what the Ross Tech computer indicated. The sensor was replaced and the light immediately triggered back on. When the computer was connected back up again this time, it claimed it was the other sensor. I held off on that repair thinking it's highly unlikely that both sensors would malfunction in perfect sync.

I made an interesting discovery. The light absolutely will not go on if there's no moisture present under the car. It's been hot and dry lately. I discovered that the ABS/Brake light will only trigger or should I say, the ABS system will only malfunction if the air conditioning is being used. That of course creates lots of water in the area of the front wheels. I'm convinced that moisture coming from the AC condensation is creating electrical issues. These same symtoms exsist on very foggy or wet days. Does anyone have a clue as to what I could look for? I really need to have this extremely irritating problem go away once and for all? My mechanic is currently stumped and this discussion board so far has never failed me.

I'd be interested to hear anyone's comments relating to the above.

Thanks in advance!

dommi3/Tiburon, California
1997 A8 4.2 Quattro
Silver/Gray/17" Audi A8 Wheels
Every Available Option
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Previous Audi

1990 V8 Quattro

[PaulW]

Don't know if you remember, but Randy had problems on his S8 with the ABS. The dealer stated that they had seen it before, it was excessive brake dust build up in the gear toothed sprocket and speed sensor if I remember correctly.

Don't know if the AC has anything to do with that, but a good cleaning of the toothed sprocket and speed sensor (it just pops out with your hand) might be in order. This could be humidity dependent.

pw

[Dommi3]

Thanks Paul:

I'll give cleaning the sensor a shot first before replacing it. I find it highly unlikely that both sensors would go at the same exact moment in time. One thing I can say is I had a very sloppy situation in that area due to a broken axle boot a little while back. I cleaned all the grease off the wheels but never went deeper than that. I had so much grease accumulating to one section of the wheel that it threw the wheel off balance. When I felt the poorly balanced wheel vibrating all the way through to my steering wheel, I realized something had happened. I wouldn't be surprised at all if it's filthy right near the sensor.

Once again, thanks for the good tip!

dommi3/Tiburon, California
1997 A8 4.2 Quattro
Silver/Gray/17" Audi A8 Wheels
Every Available Option
------------------------------
Previous Audi

1990 V8 Quattro