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2019 Terrain SLT Headlight Flickering / DRL Not Working

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Mike T. · rep 0 · May 25, 2:39 AM · 1 replies · solved · Question

Vehicle: 2019 GMC Terrain SLT

Hi everyone, I'm having an issue with the driver's side headlight on my 2019 GMC Terrain SLT. It started flickering intermittently a few days ago, and now it either doesn't turn on at all, or it's very dim. The DRL (Daytime Running Light) on that side is also not working.

The passenger side headlight and DRL are perfectly fine. I've checked the bulb, and it looks okay, but I haven't swapped it yet. Could this be a wiring issue, a fuse, or something more serious like a headlight module?

Any suggestions on what to check first? It's getting unsafe to drive at night.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:39 AM

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ClearTheCode admin answer: A flickering or non-functional headlight and DRL on your 2019 GMC Terrain SLT, especially on one side only, points to an issue within that specific circuit. Given modern headlight systems, it could be a few things beyond just a simple bulb.

Here’s a systematic approach to diagnose the problem:

  1. Bulb/LED Unit Check:

    • Swap Bulbs (if applicable): If your Terrain uses replaceable halogen or HID bulbs, try swapping the driver's side bulb with the passenger's side (if accessible and identical). If the problem moves, it's the bulb.
    • LED Headlights: If your Terrain has integrated LED headlights, the entire LED unit or its driver module might be failing, as individual LEDs are not typically replaceable.

  2. Wiring and Connector Inspection:

    • Visual Check: Carefully inspect the wiring harness and connector leading to the affected headlight assembly. Look for any signs of corrosion, fraying, cuts, or loose connections. Rodent damage can sometimes be a culprit.
    • Ground Wire: Ensure the ground wire for that headlight is clean and securely attached.

  3. Fuse Check:

    • Consult your owner's manual for the location of the fuses for the left-hand headlight and DRL. Check them for continuity. A blown fuse would typically result in no power at all, but sometimes intermittent issues can be related to a loose fuse.

  4. Headlight Control Module/Ballast:

    • If your Terrain uses HID (Xenon) headlights, there's a ballast (igniter) that powers the bulb. A failing ballast can cause flickering or complete failure.
    • For LED systems, there's often an LED driver module.
    • The Body Control Module (BCM) also plays a role in controlling lighting.

When to See a Shop: If swapping bulbs doesn't resolve the issue, and you've visually confirmed no obvious wiring damage or blown fuses, it's best to take your Terrain to a GMC dealership or an automotive electrical specialist. Diagnosing issues with integrated LED units, ballasts, or BCM-related lighting faults requires specialized tools and expertise. They can check for fault codes stored in the BCM related to lighting circuits, which generic OBD-II scanners might not pick up. Driving with a compromised headlight is a safety hazard and illegal in many areas, so address this promptly.

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