Zorb

On my 2007 Cobalt, the auto function for headlights is not working correctly. If the setting is "auto" then the daytime running lights (DRL) should be on in the daytime and the headlights at night. In my case, the headlights are always on. This causes the dash displays to dim and be virtually unreadable during the day; it's also a waste of headlight and parking light life.
The light sensor tests ok and the wires leading to the sensor have a 5V reference signal which I think is correct. The DRL fuse is also ok.
I'd appreciate any ideas on what else to check?

EinST

Welcome to the forum. Your symptoms are consistent with the BCM sensing a fault on the ambient light sensor circuit, i.e., the automatic lamp control is inoperative and defaults to the low light status. How did you test the sensor?

Zorb

I tested the sensor three ways. First, I disconnected it from the wiring harness and checked that the resistance across the terminals; resistance varied depending on how much light was on it. Second, I checked the voltage across the sensor when it was plugged into the harness; the voltage varied from about 0.7V to 4.6V depending on the amount of light. Third, I checked the voltage across the sensor as seen at pin 44 of the Body Control Module (BCM) C2 connector; that reading matched the reading at the sensor.

Since the sensor seems to be working as expected, I'm thinking it's either an intermittent sensor problem, a connection problem, a relay somewhere, or maybe an issue with the BCM. I'm still fiddling with it.

EinST

It could even be a malfunction in the turn signal MFS. It probably boils down to what the BCM is sensing and commanding but without a sophisticated scan tool, it's near impossible to work on it nowadays.

Zorb

Somewhere during the process of checking all of the headlight and DRL sensor signals at connector C2 of the BCM I noticed that the lights seemed be working correctly. I've been watching things for a day now and the daytime running lights, auto lights, and headlights seem to be working properly again. I suspect a bad connection at the C2 connector was to blame, and removing/reseating the connector during testing was enough to improve the connection and fix the lights.

EinST

Congrats. Thanks for the update.

geroy1212

I am too having problems out of my 2010 Chevy Cobalt drl.It has been in the shop twice in the last three months for the same thing.I have even sent gm a email about this problem.

Chevrolet Customer Service

<!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:PunctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:Compatibility> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <wontGrowAutofit/> </w:Compatibility> <w:BrowserLevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]--><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]--> geroy1212,

Is your problem the same as Zorb's? You stated you've taken the vehicle in twice for this issue, were they able to offer possibilities?

Any additional information you can provide may help.

I look forward to your reply.

Louis
GM Customer Service

geroy1212

They replaced the bcm modular but it is still did not fix the problem.And I get a message saying the auto lights are off when the switch is turn on,I have to turn the switch off then back on.As soon as I can I am going to trade this car off and get me something else.And I am sure it will not be made by Chevrolet.

bradhohio

The daytime running lites are the headlights. They are supose to be on in the daytime.