So first make sure 60 ohms from CCH to CCL with power off, that’s 120 ohms at the IOD (actually from CPUA jumpers) and 120 ohms at the CWIL (resistor soldering the board). A good CAN channel should read about 2.5vdc from high to ground and slightly less from low to ground and should be fluctuating. If it’s much off of that you want to unplug boards until you find which is causing the problem. Ideally, you would have started with just the new CPUA, IOD, & CWIL with nothing else attached to the CAN channel and see if you could get the MAINCOP to show up with a 1 when you type in a DCN command. Then add the door board, then selector. If one of those causes you to loose CAN then that board is bad. Also beware of the CE electronics board in the controller, if you have one, I’ve seen that pull down the whole C channel. And at a minimum after replacing those 3 boards you’ll have to load the job & generic in the CPUA, do a TECC to teach the CWIL, and do an SPC with the SP jumper on pins 1-2.
