# DRL and Auto Headlights Not Working



## tsheward (Mar 12, 2015)

I have a 2012 Cruze Eco and this morning discovered that the DRL (daytime running lights) didn't come on when I started the car. I'd noticed the auto headlights acting a little odd the last few days (not coming on or staying on once it was light enough for them to go off) and the Infotainment (radio) screen was randomly brightening and dimming even when the headlights were not on. When the DRLs didn't come on this morning, I switched the auto headlights off and back on and they didn't come on. The regular headlights are working fine. When I came out from work, I turned the auto lights on in the parking garage and the dash indicator came on but the lights were not on.

When I got home this evening, I sat in the driveway with the car idling and watched the battery voltage readout on the dash when I turned the lights to auto - it was dropping like a rock when the lights were in auto mode (but not lit up).When I turned the auto off and killed the engine and restarted it, volts were back up to 14.4. Any ideas?


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## ChevyGuy (Dec 13, 2014)

Have your headlights been modified in anyway? That sure sounds strange. 

If your '12 is like my '13, the BCM handles the low beams. So if the low beams work, then all the ciritry associated with headlights is fine - but that doesn't explain why the DRLs doesn't work. It's all the same wires and modules. Only the high beams go a different route.

The radio brighten/darken seems to be based on the light sensor - the same one that drives the lights in auto mode. But when you manually turn things on, it seems to brighten/darken based on light and not if your lights are on or not. So it might be a defective ambient light sensor.

The voltage drop is puzzling. Does the voltage drop when you turn on headlights? Perhaps you've got a the bad ground cable, or your alternator is weak.

At this point I think the BCM is either defective or confused. But if confused, what's confusing it. (Classic computer troubleshooting problem.)


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## tsheward (Mar 12, 2015)

Thanks, ChevyGuy. The headlights have not been modified in any way, not even a bulb replacement. The low beams work fine - we had some nasty fog this morning so I used them using the manual switch and not the auto, no issues.

I was thinking the same about the ambient light sensor since it controls both of those issues.

Voltage seems to be steady when the lights are manually on, only in auto does it start dropping significantly. I have an appointment to have it looked at on Fri so hopefully they'll have some answers.


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## NickD (Dec 10, 2011)

Sure sounds like this non-clamping negative ground battery terminal problem. Caught this on day two of getting my new Cruze. My main objective was to add silicone grease to the terminals to help prevent corrosion. Came from the factory bone dry.

I removed the cable and bolt, spread the tabs and filed in between the tabs so would be a gap. Then only three years later get a letter from GM that this can be a problem. I could hand twist that negative battery terminal on mine. 

Battery is far more than an electrical storage device to start the vehicle, it is the key filtering element to handle the transients generated by the alternator. And believe me, those microcontrollers are sensitive. 

Also wasn't to keen on the idea of placing all those positive battery leads terminal block so close to the battery, so greased and tightened all of those. Noted, this is an area that has to be inspected frequently.


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