I just purchased this 2001 Prius. The hybrid battery pack was totally discharged. I replaced the battery pack along with several fuses. The car started and ran fine. After a day or so I started the car and drove it a few miles. As I was driving, "check engine" display came one. Shortly thereafter, at a stop, the car "died". After some checking, I put a booster on the 12V battery and drove it home. As I was driving it the "check engine" display was still on. What should I look for to determine the problem with this car?