http://www.318ti.org/notebook/asc/index.html"There are some differences about what ASC + T has to deal with compared to ABS. ABS has to control the braking force at all four wheels. ASC + T has to control the power delivery of the engine, and the way the rear differential distributes torque between the two back wheels."
"The ASC + T system determines that a wheel is spinning by comparing the rear wheels' speed to the front"
"The ASC + T system intervenes in two stages: When it detects one rear wheel near the threshold of adhesion, it starts to rapid pulse the brake to that wheel (just like ABS). When the second rear wheel nears the limit of adhesion, engine power is reduced."
"The first stage (single wheel braking) actually improves vehicle performance. The second stage (engine reduction) doesn't improve performance available, but it adjusts output so that all that is available is fully utilized.
The dashboard ASC + T light only flashes when the system enters the second stage, and is reducing engine power. It doesn't flash when the system is only braking a wheel about to slip."