I've also seen similar errors when reading data from a G5.
The problem was that when the ignition key was moved slightly (between the "ignition on/off" positions), various lights (such as the parking light and instrument panel illumination) would flicker.
We blamed it on the "E-part" of the ignition switch back then.
Whether that was really the solution, I can't say, because the customer didn't find the fix to be that important (despite the warranty

).