auto headlights not working properly

2009 PONTIAC G8
155,000 MILES • 3.6L • 6 CYL • 2WD • AUTOMATIC
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ZORRO9099
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  • 24 POSTS
Upon starting the vehicle, the headlights come on even in broad daylight, to get them off I have to manually turn the headlight switch. Is this a bad ambient sensor, or something else? If the sensor is that easy to change, does part of the dash just pop off?
Feb 16, 2022 at 8:49 PM
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KASEKENNY
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I think you are exactly correct. Basically, the way this works is when the ambient light is low it causes the sensor to send a voltage signal that the BCM interprets that voltage as low light and turns on the auto lights.

When the sensor fails the BCM thinks that it is dark, so it keeps the lights on.

I would suggest checking the voltage when the sun is out and then when it is dark. Pull it in and out of the garage and the voltage should change.

Here is a guide that will help with this testing:

https://www.2carpros.com/articles/how-to-check-wiring

If it doesn't change then the sensor is the issue.

Please see the wiring diagram below and let me know what you find.

Thanks
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Feb 17, 2022 at 2:32 PM