2018 GMC Sierra 1500 Fuse Box Diagram & Amperage

Quick Answer

The 2018 GMC Sierra 1500 typically has three fuse box locations: under the hood, inside the cabin (driver's side kick panel), and in the rear under the rear seat or in the cargo area.

Under-Hood Fuse Box (Engine Compartment Fuse Block)

This fuse box is located in the engine compartment on the driver's side, near the battery. It contains fuses and relays for critical engine functions, powertrain control, and various high-current accessories.

Relay Locations (Under-Hood):

• R1 (FUEL PUMP RLY): Fuel Pump Relay
• R2 (STARTER RLY): Starter Relay
• R3 (RUN/CRANK RLY): Run/Crank Relay
• R4 (A/C CLUTCH RLY): A/C Clutch Relay
• R5 (COOL FAN 1 RLY): Cooling Fan 1 Relay
• R6 (COOL FAN 2 RLY): Cooling Fan 2 Relay
• R7 (HEADLAMP RLY): Headlamp Relay (controls both low and high beams in some configurations)

Instrument Panel Fuse Box (Driver's Side Kick Panel)

This fuse box is located on the driver's side, behind the kick panel next to the footwell. It houses fuses for various interior electrical components, infotainment, power windows, and other cabin accessories.

Rear Under-Seat/Cargo Area Fuse Box

Depending on the trim level and configuration, some 2018 GMC Sierra 1500 models may have an additional fuse box located under the rear seat or in the cargo area. This box typically handles power for rear-specific features, trailering, or high-draw accessories in the cargo area.

How to Test a Fuse

Testing a fuse is a straightforward process that can help you diagnose electrical issues. Here's how:

1. Locate the fuse box: Refer to your owner's manual or the diagrams above to find the correct fuse box.
2. Identify the suspected fuse: Use the fuse diagram to find the fuse for the circuit you are troubleshooting.
3. Visual Inspection: Most automotive fuses have a small wire or filament inside. If this wire is broken or melted, the fuse is blown. Some fuses are opaque, requiring a different method.
4. Use a fuse puller: Most fuse boxes come with a small plastic fuse puller tool to safely remove fuses.
5. Use a multimeter or test light:
   • Multimeter: Set your multimeter to the continuity setting. Touch one probe to each metal terminal of the fuse. A good fuse will show continuity (a beep or a reading close to zero ohms). A blown fuse will show an open circuit (no beep or "OL" for overload).
   • Test Light: With the ignition on (or the circuit powered), touch the tip of the test light to the small metal test points on the top of the fuse. If the light illuminates on both sides, the fuse is good. If it only illuminates on one side or not at all, the fuse is blown.
6. Replace with a new fuse: Always replace a blown fuse with a new one of the exact same amperage rating and type. Using a fuse with a higher rating can lead to serious electrical damage or fire.

Common Blown Fuses on This Vehicle

While any fuse can blow, some circuits are prone to experiencing issues due to wear, accessory usage, or specific component failures. On the 2018 GMC Sierra 1500, common blown fuses (and what to check first) include:

• Cigar Lighter / 12V Power Outlets (F3/F4 Instrument Panel, F4 Rear): These fuses often blow due to overloading from charging multiple devices, using high-power accessories, or a foreign object shorting out the outlet. Check the devices being plugged in for faults.
• Blower Motor (F5 Instrument Panel): A failing blower motor can draw excessive current, causing its fuse to blow. If your A/C or heat fan isn't working, check this fuse. A clogged cabin air filter can also put a strain on the motor.
• Radio/Infotainment (F2 Instrument Panel): Issues with the radio itself, connecting faulty USB devices, or wiring problems can sometimes cause this fuse to blow. If your radio is completely dead, this is a good place to start.
• Headlights (F9-F12 Under-Hood): While less common than accessory fuses, a short in the headlight wiring or a failing headlight bulb can sometimes cause these fuses to blow. If one headlight is out, it's worth checking the specific fuse.
• Trailer Brake Controller (F16 Under-Hood): If you're experiencing issues with your trailer brakes, or if an accessory connected to the trailer wiring has a short, this fuse can blow. Always check your trailer's wiring for any obvious damage or shorts.

Remember to always consult your vehicle's owner's manual for the most accurate and detailed fuse box information specific to your trim level, as configurations can vary.

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