Dim headlights

Tiny
CHARLIE1229
  • MEMBER
  • 2014 GMC SIERRA
  • 6.2L
  • V8
  • 4WD
  • AUTOMATIC
  • 38,000 MILES
For some reason my headlights, both low and high, seem to be really dim. I thought it may have been my bulbs so I bought new LED's. They also do not seem to be as bright as they should be. I know someone who has a very similar pair and they are very bright. Any ideas what it could be?
Saturday, February 10th, 2018 AT 5:01 PM

5 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 34,090 POSTS
Have the charging system tested. You can start the tests by measuring the battery voltage while the engine is running. You should find between 13.75 and 14.75 volts. If that is okay, it means it is okay to have the rest of the tests performed, but you need a professional load tester for that. Of particular interest is the full-load output current and the "ripple" voltage. If they do not provide a printout of the test results, ask to have the numbers entered on the invoice so you can share them here.
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Saturday, February 10th, 2018 AT 5:21 PM
Tiny
CHARLIE1229
  • MEMBER
  • 46 POSTS
Okay thank you, I will work on getting it tested.
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Saturday, February 10th, 2018 AT 6:21 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 50,271 POSTS
It sounds like you have one or more BCM fuses that are out or the BCM is out causing the headlights to be dim. Here is a guide to help you test the fuses:

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Here are the fuse and BCM locations. I would also check the ground for the system on the lower left of the engine.

Check the wiring as well before you replace the BCM.

Check out the diagrams (below).

Let us know what happens and please upload pictures or videos of the problem.

Cheers, Ken
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Monday, February 12th, 2018 AT 12:06 PM
Tiny
CHARLIE1229
  • MEMBER
  • 46 POSTS
Just an update. So I checked my battery voltage and it was around 12.4 and 14.6 when started. So my battery and alternator appear to be ok. I also checked all 4 BCM fuses and they were in working condition. Took a look at the ground wire and even grinded the frame down a little to assure a good connecting.
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Wednesday, February 21st, 2018 AT 6:19 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 50,271 POSTS
Its not an alternator or battery issue you are right about that. My next check would be to take the BCM connector and check the power and grounds. If all are okay I would say the BCM is bad and you will need a new one. It will need to be programmed by a shop or the dealer.

Here is a guide to check the power and grounds. Use the wiring diagrams above to check.

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

Please let us know what happens.

Cheers, Ken
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Wednesday, February 21st, 2018 AT 9:58 AM

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