Codes Question

[8202632]

Have a really stupid question.  If an electrical part has failed, should it be assumed that a code will exist in the system?  It is a hard and fast rule?

 

For example, my auto headlight sensor.  I've noticed many times now that the headlights will come on in the bright sunlight when they shouldn't.  This happens intermittently (and no my DRLs are not set to "on"). 

 

So will a code show up?  If not, does it have to wait till complete failure?  If no code is thrown, will a technician simply report that the fault cannot be replicated?

 

I have another issue with my compass not being displayed about 1/2 the time and the dealer usually responds that they cannot diagnose.

 

Any help and insight would be appreciated!

[ARModen]

The automatic headlights won't throw a code.  The sensor says the headlights need to be on and they're on, everything is good as far as the car can tell.  You'd get a code if the headlight did not come on as it was supposed to.