Electronics manufacture, you can run some pretty wicked tests. hell of a screening process.
IIRC 95+% of the stuff that came back for check was found to be fine.
Car came in with an issue, dealers made silly money off shotgun approach (just swap a few parts all at once).
Testing, isn't just pass/fail. They look for issues that could come up later. Pretty fine toothed comb.
When stuff was bad, and caught in house............usually it was a supplier part or equipment issue that F'd em.
Delco used to have a team of engineers that went to suppliers and helped them get their acts together.
Caught a few that lied about their processes and testing too. Sunsabitches.
This doesn't explain why GM can't make a passenger window switch for a P/U truck that lasts more than 23 months.
