By now, most of us have had to deal with a CAN (Controller Area Network) communication “U” series code at one time or another. Most of the time, diagnosing one these codes is fairly straightforward, given all of the articles and technical publications that have been written regarding these problematic codes. In most cases, it just comes down to identifying the module that isn’t communicating with the other modules on the CAN bus line for whatever reason. Generally, it’s some type of lost voltage or a poor ground in the circuit wiring to the module in question. So, what happens when all your diagnostic tests and checks take you down a dead-end road, and the actual problem ends up being a component that shouldn’t have had anything to do with a communication error code? I’m sure there may be a few engine drivability techs out there who have run into the situation that I’m about to cover, but it was a first for me.