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goodwrench9124, ASE Certified Technician
Category: Chevy
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Experience:  Ase Master Certified, GM Master Certified Tech. Awarded GM Top performer, Hybrid certified
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Both low beam headlights/running light stopped working at ...

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Both low beam headlights/running light stopped working at the same time. High beam continue to work properly. 10 amp fuses are OK for both low and high beam. Do you think it might be a "relay" problem?

Hello, it could be the low beam headlight relay, there is three basic parts to the headlight system, the headlights, the relay for the head light, and the body control module. you can do a couple of different things to help isolate problem. try swapping head light relay in the fuse block with a another relay of the same part number in the fuse block. the part numbers are located on top of each relay. if you have a test light, you can touch each low beam headlight fuses and see if the test light comes on with the low beams on!! i have also included the wiring diagram to help. just fyi, i have seen both low beams burn out at the same time. besure to verify the bulbs are ok.

Object Number: 675947  Size: FS



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The headlamps may be turned on in 2 different ways. First, when the driver places the headlamp switch in the HEADLAMP position, normal operation occurs. Second, with the headlamp switch is placed in the AUTO position, automatic lamp control (ALC) occurs. During ALC control, the headlamps will be in daytime running lamp (DRL) operation in daylight conditions, or low beam operation in low light conditions.

The HDM and high beam relay receive battery positive voltage directly from the battery. The BCM supplies a 100% duty cycle PWM ground signal to the HDM for automatic headlight control and normal headlight operation. The BCM also supplies ground to the high beam relay coil for high beam headlight operation. When the driver places the headlamp switch in the HEADLAMP position and the dimmer switch is in the low beam position, the HDM switches to full output sending current flow through the left and right low beam headlamp fuses to both low beam headlamps. The dimmer switch sends a ground signal to the BCM in the high beam position and a momentary ground signal in the flash-to-Pass (FTP) position from G102 to deactivate the low beam headlights and activate the high beam headlights. With the headlights in the low beam position, the high beams may be momentarily turned on or flashed by activating the FTP portion of the switch.