I have one headlight on my 2015 GMC 2500 slt pickup that ...


I have one headlight on my 2015 GMC 2500 slt pickup that will not shut off. It does not go off no matter what position headlight switch is. With key removed doors locked still on. Mechanic's Assistant: Have you checked the...

I have one headlight on my 2015 GMC 2500 slt pickup that will not shut off. It does not go off no matter what position headlight switch is. With key removed doors locked still on. Mechanic's Assistant: Have you checked the fuses? Have you checked the bulbs? Yes Mechanic's Assistant: Are you fixing your GMC 2500 yourself? What have you tried so far? Yes to myself. Pulled wire to headlamp light will go out. Plug back in , light will stay out for a very short time then com back on. Have to [disconnect battery](/topics-disconnect-battery/) to shut off. Tried every position on light switch does not make any difference. Mechanic's Assistant: Anything else you want the Mechanic to know before I connect you? It seems to have started doing this after I shut off headlight with switch while truck was running then turned on to drive. Later parked and came on after truck shut off.

Automotive Expert
Hello and thank you for choosing JustAnswer. Sorry to hear you are having this problem with the GMC My name is \*\*\*\*\* \*\*\*\*\* I will do all I can to assist with this issue. You may receive an Automated prompt for a phone call. There is an additional fee for the call and is NOT required. Continuing with the **Chat** is my **Preferred** method. **(I have attached a document(s) to this thread. Please let me know if it does not show up on your end or if you have any problems opening the file. Note: Attachments may not show up if you are using a mobile device, go to your last e-mail from JustAnswer and you will see the attachment.) Note: Document links will automatically delete after 7 days.** Have a look at this wiring diagram for reference (See attached) [https://www.dropbox.com/s/s0y3q6kre7o8h4n/Headlights%20BCM.pdf?dl=0](https://www.dropbox.com/s/s0y3q6kre7o8h4n/Headlights%20BCM.pdf?dl=0) The low beam headlights are controlled by the Body Control Module. Whereas the High beam headlights incorporate a relay, the low beams are connected straight to the BCM. The ideal way to approach this problem is with a scanner (Tech 2 or similar) that is capable of communicating with the BCM to check for any stored Diagnostic Trouble Codes as well as monitor all inputs and outputs to the BCM. Unfortunately, the cost of this type scanner puts it out of reach for most unless you are a shop that specializes in GM repairs. It is unlikely that it is related to the switch as it provides the input to the BCM to turn on the low beam headlights (as a pair, not individually) See attached. [https://www.dropbox.com/s/01ulcud87mh4m2h/Headlamp%20Switch.pdf?dl=0](https://www.dropbox.com/s/01ulcud87mh4m2h/Headlamp%20Switch.pdf?dl=0) In the absence of a fully compatible scanner to assess the BCM, a hard reset at the battery and checking ALL of the vehicle fuses with a test light are your only options. <u>Hard Reset</u> – Disconnect both battery cables. Touch the cable ends together (away from the battery) for 15 seconds. Reconnect the cables _ **Positive Cable First** _ to avoid any voltage spikes. Touching the cables together drains the reserve voltage in the Module Capacitors causing the Modules to reset and re-establish communications. This might resolve the issue. NOTE – This procedure will erase radio, seat, mirror (ect.) memory pre-sets and the radio code may be required. If the issue persists, check ALL of the vehicle fuses with a test light. Since the BCM has multiple power inputs and relies on communication with other modules to function properly, sometimes a seemingly unrelated fuse can have strange consequences. Visually inspecting the fuses will not suffice. Here is a link to a video that illustrates this test (Note: it is a different vehicle but the process is the sam. [http://https://ytcropper.com/cropped/o\_5e3b841e54b87](http://https://ytcropper.com/cropped/o_5e3b841e54b87) I hope this helps. Please let me know if you have any questions. Note: If I don’t immediately respond, I kindly ask for your patience, I will reply as soon as possible. Thank you for choosing JustAnswer. 100% Customer Satisfaction is my goal. If you are satisfied with my answer please don’t forget to rate my service. (Where the stars are by “Rate my Service) If for any reason you are not satisfied with the answer I have provided, please let me know

I viewed your response and tried the procedures that you recommended. It did not solve the problem but I did discover that I have a after market XenonDepot light system installed. I contacted the company and it looks like there maybe a relay in the harness that has failed. The company is sending me parts that should fix the problem, thanks for you assistance. Joe

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