Please help!!!

I have a 97 E320, that doesn't shift out of low gear. One night on my way home I ran over a metal object on the highway and it hit the bottom of the car really hard, 2 days later my "Check Engine" Engine Electronic light came on and the car won't shift out of 1st gear, my mechanic reset the check engine and the car runs fine, the next day the car does the same thing again. Then he told me that I need a ABS speed sensor which I got, he installed it, reset the check engine and the car runs fine again, the next day the car does the same thing. Now, he's telling me to order the ABS pump, which costs $1940.00 which the dealer has never even sold one before. The car probably doesn't even cost that much. People mention limp mode.