My son has a 2000 Saturn SL2. The service engine soon light came on, the speedometer quit working & the car jumped when putting it in drive. When driving it shifted hard. I took it to a mechanic & was told the speed sensor had gone out. I had it replaced & less than 2 weeks later it happened again. I took it back & they reset it & said a bunch of transmission codes popped up but they weren't sure what was wrong. Well, 2 days after resetting it, the check engine light is back on & it's driving weird as my son says...he said the speedometer is still working & it didn't jump when shifting into drive but it just didn't feel right. He wasn't able to describe the problem other than it feels like the transmission isn't right. I drove it last night & all was fine. What sort of transmission problem causes this & is there something that can be repaired to hopefully avoid having to replace the transmission?