Inspect the vehicle ECM using check mode. Intermittent problems are easier to detect with the GTS when the ECM is in check mode. In check mode, the ECM uses 1 trip detection logic, which is more sensitive to malfunctions than normal mode (default), which uses 2 trip detection logic.
Change the ECM from normal mode to check mode using the GTS.
Check and wiggle the harness(es), connector(s) and terminal(s).