How to Replace a Fuel Filler Cap

The fuel filler cap secures the entry to the fuel tank of a vehicle and it is made of metal or plastic.

Most fuel filler caps have threads, which are fixed to the tank pipe with matching threads. A rubber gasket at the top is compressed when the cap is fixed and it stops fuel and fuel vapor leaks. The fuel filler cap also has air vents that allow the air to enter into the tank and maintain pressure.

Generally, fuel filler caps can be used as a closure for the fuel tank. Most fuel filler caps are sealed by turning them until you hear a clicking sound. Other caps have locks within them requiring a key to open them.

  • Note: It is not recommended to use a fuel filler cap with a key insert. These type of caps generally have a small leak around the keyhole.

check engine light on the dashboard

On vehicles from 1996, the emission control system monitors the fuel vapors and illuminates an engine light when there is leakage. If the seal is damaged or if the fuel filler cap does not seal the tank properly, the engine light will be illuminated along with the fuel door light. If this light comes on, check the fuel filler cap and see if it is screwed on properly. Most of the time, the problem may be solved by replacing the defective gasket. However, cleaning the cap and/or greasing the gasket may also help in a few cases.

Signs of fuel filler cap failure

At regular intervals, ensure that you check your vehicle for any signs of fuel filler cap failure like:

  • The smell of gasoline or diesel vapors around or near the fuel filler cap
  • The gasket of the cap is split or missing
  • The cap has a crack
  • The threads on the cap are stripped

If the fuel filler cap fails, the engine management system will record this event. A fuel level sensor will send information to the car’s computer about the level and resistance transmitted to the gauge.

Engine light codes related to the fuel filler cap

Fuel leakage in a vehicle can be very dangerous. Liquid fuel does not burn, but the vapors given off by the fuel are extremely flammable. If there is a leak at the fuel filler cap, there is an increased risk of the fuel vapors igniting when rocks are thrown up into the wheel well causing a spark.

  • Warning: Do not smoke around a vehicle if you smell fuel as the fuel vapors are very flammable.

Part 1 of 3: Prepare to replace the fuel filler neck

Having all of the necessary tools and materials prior to starting the work will allow you to get the job done more efficiently.

Materials Needed

Step 1: Park your vehicle on a flat, hard surface. Make sure that the transmission is in park mode (for automatics) or in 1st gear (for manuals).

Step 2: Secure the vehicle. Place wheel chocks around the front tires that will remain on the ground since the rear of the vehicle will be lifted up.

Engage the parking brake to prevent the rear tires from moving.

Part 2 of 3: Remove the fuel filler cap

Step 1: Locate the fuel filler cap. Open the fuel door to gain access to the fuel filler cap.

Step 2: Check the fuel filler cap. Look at the fuel filler cap for any exterior damage. Remove the fuel filler cap from the fuel filler neck and remove the cable from the fuel door.

Look at the threads on the cap to see if they are stripped.

Step 3: Check the gasket. Remove the gasket that is on the bottom of the fuel filler cap. Check the gasket for any cracks or distortion.

Step 4: Check the fuel filler neck for any damage. If you notice any damage, the fuel filler neck may be failing.

Step 5: Clean the fuel filler neck threads. Use a clean cloth or paper towel to clean the threads on the fuel filler neck.

Part 3 of 3: Install the new fuel filler cap

Step 1: Install the new gasket onto the new fuel filler cap. Screw the new fuel filler cap onto the fuel filler neck. Ensure that the threads lock fully onto the fuel filler neck.

Step 2: Hook up the cable to the fuel door. Use the combustible gas detector and verify that there are no fuel vapors leaking from the fuel filler cap.

Close the fuel door

Step 3: Drive the vehicle. During the test drive, go over different terrain like bumps to allow the fuel to slosh around inside the fuel tank. This will cause the fuel to bubble up and create mass amounts of vapor.

Step 4: Check for warning lights. Monitor the dash for the engine light to appear.

If the engine light comes on even after replacing the fuel filler cap, you may need to get the fuel system checked for possible electrical issues. If the problem persists, seek help from one of the certified technicians at YourMechanic and get them to inspect the fuel filler cap and determine the cause of the problem.


Next Step

Schedule Electric Problems Inspection

The most popular service booked by readers of this article is Electric Problems Inspection. Once the problem has been diagnosed, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. YourMechanic’s technicians bring the dealership to you by performing this job at your home or office 7-days a week between 7AM-9PM. We currently cover over 2,000 cities and have 100k+ 5-star reviews... LEARN MORE

SEE PRICING & SCHEDULING

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Recent Electric Problems Inspection reviews

Excellent Rating

(717)

Rating Summary
669
17
8
6
17
669
17
8
6
17

Kanstantsin

19 years of experience
51 reviews
Kanstantsin
19 years of experience
Chevrolet Cruze L4-1.4L Turbo - Electric Problems - Englewood, Colorado
Absolutely humble and knowledgeable mechanic, he knows his work very well. I would strongly recommend him. Thanks Kanstantsin.
Volvo S80 - Electric Problems - Englewood, Colorado
Super. Friendly & efficient. Can definitely be trusted to work on your car. He knows about Volvos, particularly older models.

Alejandro

9 years of experience
82 reviews
Alejandro
9 years of experience
GMC Yukon V8-4.8L - Electric Problems - Los Angeles, California
ALEJANDRO was extremely courteous, patient, and knowledgeable. He us a great asset to your organization.
Nissan Altima - Electric Problems Inspection - Los Angeles, California
Got me the specifics for my car’s issue down to what the options are from here on out. Cool dude who was calm and collective about these issues. Will be able to want to book another appointment with him, if it is needed.

Jonathan

35 years of experience
483 reviews
Jonathan
35 years of experience
GMC Envoy L6-4.2L - Electric Problems - Clearwater, Florida
He completed what I thought was a thorough inspection and resolved my headlight issue. Thank you again!

Joe

43 years of experience
821 reviews
Joe
43 years of experience
Mercury Sable V6-3.0L - Electric Problems - New Port Richey, Florida
Well I already comment on Joe and the service he did. Like I said Joe really is concerned about your problem. He really goes beyond the call of duty. I'm so glad I went to this site. I knew when reading the profile of the mechanics,I knew I found the right one when I read Joe's profile. He really is passionate about his work. Really explains more then you would get from other places and mechanics I've dealtwith. Thank you Joe for having a great car side manner. You really put me at ease.

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

Related articles

Symptoms of a Bad or Failing Fuel Pressure Regulator
Common signs include engine performance issues, fuel leaks, and black smoke coming from the exhaust.
How Long Does a Fuel Return Hose Last?
Most Most of the older cars on the market have a carburetor that helps to disperse the fuel that is need during the combustion process. While these carburetors are very reliable, there are a number of repair issues that can...
How to Troubleshoot a Gas Cap That Won't Come Off
Gas caps stick and won't come off when the gas cap is broken, there's a mechanical defect in the gas tank filler neck, or gas cap is locked.

Related questions

Truck hard to start and seems to be a fuel injection problem.
The issue may or may not be the Fuel Injection Control Module, but the issue is certainly fuel related. I would recommend having your truck inspected by a professional who is experienced with diesel engine diagnosis. It is possible that...
Car won't start - 2004 Jeep Liberty
Hello. If the fuel injector system leaked fuel into the engine it may have caused a fuel vapor lock of the engine. A mechanic could get the engine to turn again by removing spark plugs and checking the oil to...
Why does my car loose RPM when I'm driving?
Hi there. First check all of the fluids and make sure that they are full and top off all low fluids. Then check the battery and make sure that it has a full charge of 12.6 volts. If the voltage...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 · hi@yourmechanic.com