There are a number of intermittent electrical problems that show up over time due to contamination. The top contender for signal issues are the older Bosch CAN bus, J1500 series circuits and the Newer J1900 series Data bus systems. Both are used so the Different Control modules used in the Injector pumps, ECM, TCM  and other low level controls can talk to each other. Plus any 5 volt or 12 volt wiring exposed to harsh environmental conditions or where they are exposed to moisture or dissimilar ma