2009 LT2 2.4. All stock. I work nights and do most of my driving at night. Last week when I got off work at 5a it looked like one of my headlights were out, but pulling out of the parking lot reflection in nearby window showed both on. Drove a short distance and brightness went up to normal. A night or two later the same thing happened but the headlight (driver's side) never came on. Playing with the headlght and fog light controls did not do anything, neither did pulling the relays and fuses. Then, over the weekend, everything seemed back to normal. Last night: same thing.
To be clear: the passenger side headlight works fine. Low beams work, high beams work, DRL works.
Drivers side: DRL work as normal in the day time. But at night the headlight stays in DRL mode and does not switch to full-brightness headlights. Switching between Hi and Lo beam does not change anything: the light does not even flicker. And again, this is ONLY on the Driver's side. The Passenger side works fine.
All fuses (Hi/Lo left and right and DRL) are good. Bulbs are obviously good (since the light is on, just at reduced brightness). From what I see the lights are fused separately but share a relay so if the passenger side works, the relays are good.
I've not had the time to really dig into it: I'll do that on my days off this week, but I thought I'd post for ideas first. What has me puzzled is why just one side? A complete wiring diagram of the headlight/drl system would help and I'll keep looking for one but any help there would be appreciated.

 

Welcome to the site, the DRL's use the hi beam filament, so the low beam filament might be detached but contacts periodically. Change out the both bulbs, they tend to fail in pairs!

 

X2 on the bulbs. Several folks over the years have posted about headlights doing weird things(or so they thought). Most turned out to need a simple bulb replacement.

 

The first thing I'll do when I get a chance is swap bulbs to see what happens, but I'm not optimistic because the headlight is on, just in reduced output DRL mode and the problem is intermittent (though possibly increasing in frequency: We'll find out in 8 hours...). I've had bad bulbs that would go on and off as the broken filament made contact, but never had one spontaneously dim itself. My first thought was bad ground, but then it should at least flicker when the headlight was switched from on to off or hi to lo. It doesn't Its on steady low-intensity regardless of hi/lo setting.
Also, I should have noted that the bulbs are only about 4 months old. Replaced both when I got new headlight assemblies since they were out and are real PITA to replace.

 

Correction oldblue is correct for most cars; not the HHR. DRL is full power low beam.
Most cars use low power high beams.

I suspect the bulb.

 

Ok.

 

I poked around a bit more when I got off work this morning. Pretty sure its a bad ground connection and the headlight is grounding through the unused filament. Its not in DRL mode: pulling that fuse or relay does nothing. Pulling the fuse for the hi or lo beam on that side shuts off the headlight completely, as does pulling the appropriate relay. However, if I have the low beams on and pull the hi-beam switch, the 'flash to pass' instead of pushing it to turn on hi beams', the lights go off. Since when the hi beam switch is pulled it illuminates both hi and lo beam filaments it eliminates the 'off' filament as a ground. So thats where I'll start this weekend.
Can anyone tell me where the driver's headlight grounds to?

 

Up under the drivers side fender.

https://www.chevyhhr.net/forums/how-...cations-56504/

 

Only one filament is on at a time. Hint to see a clearer image: right click on the image and select "open link in new tab".

This is for 2006; DRL is the parking lamps.


This is for later models DRL is low beam. Especially note how the DRL is wired in failsafe.

 

Awesome. Thank you. Tomorrow I'll pull the bulb and check its ground contact and the plug and go from there. Since it appears the park lights (and presumably the fog lights and maybe horn since they're all right there together) share the same chassis ground, that shouldn't be the issue.
On the hi/lo beam when you select either hi OR lo beam only one filament is on, but when you pull the switch toward you to 'flash' the brights they do both come on if the headlights are already on. Its quite noticeable in very dark areas: you can see the difference in brightness between just hi beams and both and see that the light pattern covers a wider area (both the hi pattern and the low pattern. Most cars with this style switch will do the same thing, at least of the vehicles I've driven.