your ASC works in conjunction with your ABS....
this is a very common problem. sometimes, you whole cluster would go haywire as well, with no speedo, no rpm and all the abs/asc lights turns on like a christmas tree. turn the car off and leave it stationary for a while, you restart and everything goes back to normal. happened on my e36, e39, my cousin;s e46 and e90 fresh out of the factory... sigh..
oh, one highly recommended mechanic i went to, told me to replace the whole ABS control unit to solve the damn problem. and its ONLY gonna cost me 3k for his service.... i gave him a @#@$%@@@1 for his unfounded advice.
anyway, you may do a search on this problem and there are numerous others with the same fate as you, and a very simple fixed it just to clean the abs sensor. but that would probably last you a short time with our wet tropical weather here.
anyway, a longer term solution would be to remove the abs sensor and have it clean with some brake cleaner and while the car is on the hoist, aim the brake cleaner nozzle into the hole at the axle where the sensor came out from and at the same time rotate the wheel while you are spraying it. this will clean up the all the dirt and gunk trap within the cog teeth over the years which is the main culprit that disrupt the abs sensor readings in the first place. spray the hole with pressurized air gun to remove excess cleaner and moisture, and reattached the sensor. repeat the process on all 4 wheels and you are done.