Pontiac Repair: 2008 Pontiac G6 wrecked/repaired now wont start, pontiac g6 sedan, pontiac g6

Question
I have a 2008 Pontiac G6 sedan, 2.4L automatic.  This car was in an accident before I bought it, it was hit high on the radiator support, right at the computer.  When the car was brought in, it started.  After tearing it down and repairing it (the body is 100% now), the car did start.  I drove it 5 miles or so as a test drive, parked it, and it has only started once since.  At the end of the drive, it started shifting funny (like it was "mechanically" shifting).  The electronics seem to be getting worse.  The odometer now shows 0 miles (the car has 2,500 mile on it) and my ODBII reader won't read a code at all.  There were about 5 broken wires, which were repaired well.  I've checked the wires over and over about 10 times each, my back is sore!!  Anyway, I've checked all the fuses under the hood and inside the car, they are good.  I can't check the relays, I just don't know how.  I've got a used ECU, and it makes no difference.  There have been some oddities that make me think it could be a ground.  There are obvious grounds on the strut tower and 2 more on the radiator support near the accident. I did check the fuse box and it's good, the connections to the bottom of it are solid.  A friend of a friend that is a low level tech at a local Saturn dealer brought his dealership's Tech II over and tried to do a quick scan, but he couldn't see ANY computer, transmission or ECU.  Can you give me some ideas of what to check next?

Answer
Hey Rod:

well a few things. Yes the grounds on the radiator support ate a good place to start looking which you did. That car has 2 data lines a high speed and low speed data line the engine and transmission are on the high speed data line. There are actually 2 wires that link those modules together all the other ones use a single wire. If one of those 2 wires is damaged you will not get any communication with the scan tool and also with the modules to allow the car to start and run. If you used that scan tool ther should have been a lot of communication codes in other modules that the scan tool could communicate with. So my guess is you have a wiring issue but where? The connectors on that engine computer are a micro 64 terminal and they are VERY VERY sensitive if you probe them with the wrong tool you "hog" out the terminal and it will not make good contact with the terminals in the module. Hit up you buddy from saturn to get the right probe and check every terminal for good pin fit and have him print off a schematic of the data line communications and check for continidity between all the modules. That is where I would start.