(Not a A-Body) 2001 Dodge Ram Truck "No bus" Code, Anyone!?
You guys are awesome!! I might as well change the crank sensor first, then if it's not that move on to the PCM.
If you want to get into the architecture of it, the crank sensor on a PCI bus is kind of like its own module, even though its 'only' a sensor. If the PCM can't tell how fast the crank is moving or where it is, it can't execute the other commands which are based on crank position/speed.
For communication to happen over the bus circuits, there has to be specific resistance values met based on the termination resistance values of the modules. (PCM, BCM etc. ) Messages (voltage) are sent out and returned. If one of the modules has a short, open etc. the resistance value will be incorrect and thus the voltage values being transmitted (or not) over the bus circuits will be out of range. Hence the 'no bus' message.
If the PCM was 'bad', you would probably see a multitude of other issues. Its rare that replacing a PCM will solve an issue. I'd see guys do it, program it etc., take the car for a ride and find that whatever issue was present before PCM swap is still there. Then they'd hand it off to the 'tough problem' guy and he'd find the wiring issue.
Try to use caution if you plan to mess with anything else. Once you start pulling on wires/connectors you can disturb things and cause other issues or mask the original cause of the problem.