automatic headlights problem

My wife's intrigue has a problem.... The drl works fine, but when they cut off at dusk the auto headlights do not turn on automatically.

The DRL fuse is fine,

The headlights work fine via the switch.

The sensor clearly works as it turns off the drls at dark.

I am new to the forum, But I did a search and nothing turned up.

The GM mechanic I usually deal with is also stumped.

If you have a clue, please email me direct at [email protected]

These cars have all sorts of electrical problems....alternators and Body Control Modules seem to be the primary troublemakers......