National average cost of a Gas Cap Replacement for popular vehicles:
Avg. cost $152
What is a gas cap and how does it work?
The fuel tank filler cap, better known as the gas cap, is more than a simple cover for the opening where you add fuel to your vehicle. Naturally, the gas cap serves as a cover for the fuel filler neck that leads to the fuel tank. It prevents fumes from escaping, yet is easy enough to remove when refueling at a filling station. But the gas cap also allows the fuel system to release excessive pressure or vent excessive vacuum that builds up in the tank. It does so with the help of two spring-loaded valves inside the cap that respond to changes in pressure, usually due to ambient temperatures. Most vehicle manufacturers recommend that you tighten your gas cap until it clicks so that the cap will be tight enough to seal and the valves will reset.
How do I know if my vehicle needs a new gas cap?
One of the most common problems that causes a Check Engine Light to come on in a vehicle is a loose or faulty gas cap. The fuel system is designed to trap fuel vapors in the system. Like a hatch in a submarine seals one compartment from another, the gas cap seals off the entryway to the fuel tank. It also allows the pressure in the tank to remain steady. When the gas cap is not doing its job properly, the engine control module will detect the problem and turn on the Check Engine Light. Other signs of a bad gas cap include
The cap will not tighten completely or remains loose
You smell fuel vapor around the gas cap even when it is tight
Your vehicle fails an emissions test
The seal or o-ring on the gas cap is cracked, deteriorated, or missing
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There is not a whole lot involved in replacing a gas cap on most vehicles. A technician would generally need to unscrew the old cap, disconnect its lanyard, attach the lanyard from the new cap, and screw the cap into place. Some vehicles, however, include a cap and seal that are integrated into the fuel door. In those cases, the entire fuel door might need to be removed and replaced.
OTHER QUESTIONS CUSTOMERS ASK
Do gas caps need to be replaced?
A gas cap only needs to be replaced if it is not working properly. Interestingly, a bad gas cap (or one that is not tightened fully) is one of the most common causes of a check engine light. If your gas cap does not tighten anymore, or if it has a cracked or deteriorated seal, it should be replaced. Same goes if your check engine light reveals that the cap is bad or your car fails an emissions test.
Can a loose gas cap cause an engine misfire?
While a loose gas cap might cause a drop in fuel efficiency, a failed emissions test, and your check engine light to come on, it typically will not cause your engine to misfire. That is because the engine control module relies on oxygen sensors to detect the air/fuel ratio and compensates for any problems that a loose gas cap can create.
Are gas caps universal?
Gas caps are not universal. The way that a cap seals inside the mouth of the filler neck varies by vehicle manufacturer and model. Besides the overall design of the cap, the thread size and pitch can differ from one vehicle to the next and will not allow them to be interchanged.