How to Replace the Fuel Cap (or Diagnose Capless Filler) on a 2018 GMC Terrain
Step-by-step instructions, required parts/tools, safety tips, and EVAP leak/check-engine light guidance
How to Replace the Fuel Cap (or Diagnose Capless Filler) on a 2018 GMC Terrain
Step-by-step instructions, required parts/tools, safety tips, and EVAP leak/check-engine light guidance
đź”§ Terrain - Fuel Cap Replacement
On most gas versions of your Terrain, the fuel system is capless (there’s no twist-off cap). If yours does have a removable cap, replacing it is quick—just remove the old one and install the correct replacement so the EVAP system seals properly (this helps prevent a check-engine light for “small/large leak”).
Difficulty Level: Beginner | Estimated Time: 0.1-0.3 hours
⚠️ Safety & Precautions
- ⚠️ Work outdoors or in a well-ventilated area (fuel vapors).
- ⚠️ No smoking, sparks, or open flames near the fuel door.
- ⚠️ Turn the ignition OFF before working at the fuel filler.
- ⚠️ If fuel was just added, wait a minute before handling the filler area.
đź”§ Required Tools
You'll need the following tools for this repair:
- Nitrile gloves
- Shop towel
- Flashlight
🔩 Required Parts
HowToo sells all the parts you need for this repair:
- Fuel filler cap - Qty: 1
- Fuel cap tether (if equipped) - Qty: 1
đź“‹ Before You Begin
- Park on level ground and switch the ignition OFF.
- Open the fuel door and use a flashlight to confirm what you have: a twist-off cap or a capless spring-loaded flap.
🔨 Step-by-Step Instructions
Follow these steps in order:
Step 1: Confirm which fuel-fill style you have
- Open the fuel door.
- Use a flashlight and look at the filler neck:
- If you see a plastic cap that twists off, follow Steps 2–5 (Twist-off cap).
- If you see a spring-loaded flap with no cap, follow Step 6 (Capless system).
Step 2: Remove the old twist-off fuel cap
- Wear nitrile gloves.
- Turn the cap counterclockwise until it releases, then remove it by hand.
- Wipe the filler-neck sealing area with a shop towel.
Step 3: Check the sealing surface
- Use a flashlight to look for dirt, cracks, or damage where the cap seals.
- Clean dirt now to prevent EVAP leak codes.
Step 4: Install the new twist-off fuel cap
- Place the new cap onto the filler neck by hand.
- Turn clockwise until it stops.
- If your cap is a “click” style, tighten until you feel/hear it click a few times.
Step 5: Reattach the tether (if equipped)
- If your cap uses a tether (the small strap that keeps it from getting lost), snap it back into its holder by hand.
- Close the fuel door.
Step 6: If your Terrain is capless (no fuel cap present)
- If there is no twist-off cap, you generally cannot replace a “fuel cap” because the vehicle is designed without one.
- Use a flashlight and check the capless flap area for dirt or a stuck flap.
- Wipe the visible area with a shop towel (do not force the flap open with tools).
- If you’re chasing a check-engine light (often EVAP leak codes), the usual fix is not a cap—it's inspection/replacement of the capless filler neck assembly or an EVAP leak diagnosis.
âś… After Repair
- Start the engine and verify the fuel door closes normally.
- If you had a check-engine light for an EVAP leak, it may take a few drive cycles to clear after the seal issue is corrected.
- If the light returns quickly, the issue may be elsewhere in the EVAP system (purge valve, vent valve, hoses, or the capless filler neck).
đź’° DIY vs Shop Cost
Shop Cost: $60-$150 (parts + labor/diagnostic time)
DIY Cost: $15-$45 (parts only)
You Save: $45-$105 by doing it yourself!
Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 0.2-0.5 hours.
🎯 Ready to get started?
HowToo makes it easy: same-day/2-day shipping on every part, plus all the tools and specialty tools you need! Check out the parts and tools sections below to add everything to your cart.
















