In our 2006 Trailblazer, we find that our low beam headlamps will suddenly go out. This is always at about twilight- when the sun is just dipping below the horizon. I have checked all relays, and was wondering if anyone has had this same problem.

Looking all over the net, it seems that it is a problem with the photo-cell ambient light sensor. The high beams work as do the fog lamps, turn signals, brake lights etc.

I have cleaned this small sensor- dome in the center of the dashboard. Any other suggestions on what is wrong?

Thanks in advance.

I know there is a way to test them, Yet I don't know how. I think they work on resistance.

Moved to Chevrolet section

To test you just take it out of the dash and hold a multimeter to it in both bright light and with the sensor covered so it thinks its darkness. One of the readings should have infinite resistance (varys by sensor as to which condition is open and which is closed circuit) and the other should have a numerical reading of resistance. The Bonnevilles for instance have a reading of around 100 Ohms in daylight and infinite in darkness.