Help! My 2002 Chevrolet Trailblazer’s headlights choose when they go on and off. They’re usually set on automatic, but even when we manually turn them on, they’re fickle. Which leads to me having to use my brights - which I don’t feel safe using for long periods of time. We used to think that the humidity in the air had something to do with it…we lived in New Orleans and it would always happen after a rain storm. However, we’ve since moved to Boston, and its happening more and more often. We’ve taken it to a couple of mechanics who look at us like we’re nuts (probably because it never happens when we’re there). Can you help?
There are a number of possibilities. First, I would make sure that the sunload sensor (that small dark tinted raised lens) on the dashboard is not obstructed. That is used to determine when to turn on/off the headlamps or DRLs.
The next thing I would try is to replace the Headlight Driver Module (HDM). This is #46 in the underhood fuse block.
If this doesn’t work, then you need to start the real diagnosis. That starts with checking the low beam headlamp output from the Body Control Module (BCM) when the problem exists to see if the BCM is commanding the lamps on (PINK/WHITE wire at pin A5).