GMC Sierra T1XX (2019-Present) headlights flicker, what should I check?

Learn how to diagnose and fix flickering headlights on GMC Sierra T1XX (2019-Present). Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Gather tools: OBD-II scanner, multimeter, socket set, screwdriver set, wire brush, and electrical contact cleaner.
• Disconnect the vehicle battery to ensure safety while working on electrical components.

2. Battery Inspection

• Sub-step 1: Remove the battery terminals using a socket wrench.
• Sub-step 2: Clean the terminals and battery posts with a wire brush.
• Sub-step 3: Reconnect the terminals, ensuring they are tight and secure.

3. Relay and Wiring Check

• Sub-step 1: Locate the headlight relay in the fuse box (refer to the owner's manual for location).
• Sub-step 2: Remove the relay and inspect for signs of damage or burnt contacts.
• Sub-step 3: Test the relay using a multimeter to ensure it clicks and has continuity.
• Sub-step 4: Inspect the wiring harness leading to the headlights for any frayed wires or loose connections.

4. Bulb Inspection and Replacement

• Sub-step 1: Open the hood and access the headlight assembly.
• Sub-step 2: Remove the headlight bulbs from the socket.
• Sub-step 3: Inspect the bulbs for any signs of damage such as dark spots or broken filaments.
• Sub-step 4: Replace the bulbs with new, compatible bulbs if damaged.

5. Alternator Testing

• Sub-step 1: Reconnect the battery and start the vehicle.
• Sub-step 2: Use a multimeter to check the voltage at the battery terminals (should be between 13.7V - 14.7V).
• Sub-step 3: If the voltage is below this range, replace the alternator.