2006 Chevy Impala no Crank after working on ECM

Car: 2006 Chevy Impala SS (5.3)

We’ve had ongoing problems with our ‘06 Impala, with the most relevant issues being the battery sporadically being drained when the car sits for a few days (not consistently) and code p0481 (Fan 2 control circuit).

We still have no idea for the battery drain, but we think we figured out and fixed the code. We check voltages for the wire between the ECM and the relay for fan 2, and determined there seems to be a partial break somewhere in the wire. We spliced in a bypass, and the code never came back.

We decided to completely get rid of the old wire, so we took the pin out of the plug into the ECM, cut off+removed the old wire, and soldered the replacement wire. We put the pin back in and hooked everything back up. There was a little miscommunication and we didn’t disconnect the battery before replacing the wire, which may be relevant to the new problem.

Now after replacing the wire, the car doesn’t crank, and we can’t figure out why or what to do. There doesn’t seem to be voltage to the starter relay, which seems to be controlled by the BCM, but it could just be communication with the ECM. We’ve tried resetting all the computers by shorting the car, but no matter what we do we can’t seem to get it to crank.