Communication problem

Hello all, customer brings the vehicle in because “the brakes are locking up” (he says.) After some discussion we find out that the actual problem is that intermittently he cannot get the vehicle out of park. When the vehicle does not come out of park, you have no comms with any module on the vehicle but it will start and run. All of a sudden you'll have comms and the vehicle will come out of park and you will have communication codes for almost all the modules on the vehicle. I scoped the comm lines at the ECM and they both go from around 2.5V to around 1.5V, they mirror each other identically, appearing as if they're shorted together.. Anybody out there dealt with this problem in the past and what was the fix for it?? I am not afraid to test, I just don't want to waste the rest of my life testing when there's somebody out there that dealt with this problem or if there's a known cause for it. Thanks in advance for all professional polite responses!!