2001 prius code 3100 with sub code #172

Hi , I have a problem with a prius that I have been working on that i cannot figure out yet, Its a 2001 with approximately 140,000 miles on it. The car came here for ABS lights on. found bad wire and fixed bad wire. had car sitting outside for a few days and got some rain in the engine compartment. So now what happens is car will not go into ready mode and when you try to start the car the engine will start to rotate just a little bit until something makes a loud bang noise in the transmission. if you try to start it again engine does not rotate. put it in nuetral and roll the car a few feet and go back into park .now car will sometimes start ,but will not charge main battery and both radiator fans run wide open. try to drive the car and engine revs up to approximately 2500 rpms and it will move forward ,but no reverse..So in short here is what I have tried, replaced HV ecu with a known good one= no difference. Replaced inverter with another one= no difference..traced all the wiring harness and could not find any problems. Any body out there with ideas or known fix?? Forgot to mention the only codes that come up is c1259 which is just the usual HV problem code ,and the other code is p3100-sub code 172. thanks