I encountered some very strange problem with my 97 E420 (80K miles) this morning while stuck in a big traffic jam in southern CA. I was in the traffic jam for over 2 hours barely traveled 2 miles within that time because of a big tanker truck accident and the resulting freeway closure. All of a sudden, the little red ASR malfunction lamp came on at the left side of the instrument cluster and the engine immediately lost almost all power. I was lucky enough just able to pull over to the shoulder and stop the engine. At the time when this happened, all other functions seem normall. After waiting another 2 hours for the tow truck, I started the car and the engine ran normal again as if nothing had happend. This time there was no ASR malfunction light and I was able to contine my trip without further problems . My question is why did the ASR malfunction light came on when the rear wheels were barely moving forward and not even slipping? Is my car's ASR system about to fail and what is the typical cost of fixing these problems. Thanks in advance for any tips.

Garry