What Does The Check Fuel Cap Light Mean?

Find out if you’re overpaying on car insurance using our cost calculator! Save money by comparing quotes from over 30 of Canada’s top insurance providers!

The best part? It’s FREE!

check fuel cap

It’s no fun to drive and see a dashboard warning light flashing on your face. However, the Check Fuel Cap light is modest compared to other warning lights. When owning or driving a vehicle, it is essential to understand the meaning of each warning light the dashboard could flash at any time.

Thankfully, the check fuel cap light is not as scary as you would believe. There’s no need to be frightened or panic. However, fuel caps are still critical, and you shouldn’t overlook them. 

A general misunderstanding is that a fuel cap’s only role is to serve as a lid for the fuel tank. It does various functions and is an integral part of the Evaporative Emission Control System (EVAP). Whenever the fuel cap is broken or not securely attached to the fuel tank, it may decrease engine performance, cause the evaporative emission control system to fail, decrease gas economy, and cause fuel leakage.

Our car’s fuel tank feeds fuel to the engine, which is ignited. Additionally, vehicles may have some fuel that has vaporized and is being used up by the engine. The evaporation of the gas is gathered in a separate tank known as the charcoal canister.

When certain driving circumstances are reached, an engine valve opens, allowing the fuel fumes to mix with the remainder of the fuel being burnt. The fuel cap must be completely sealed so outside air does not mix with the fuel tank, ensuring that the fuel system operates effectively.

The rubber or silicone O-ring on most fuel caps prevents vapours from escaping once the cap is sealed. While you run your car, it can detect potential leaks and alert the driver if a problem is identified.

What Is A Fuel Cap and Its Functions?

This seemingly simple cap, which you twist off and on each time you top up your fuel tank, bears a more significant duty than you would believe. The fuel cap’s purpose is to keep dirt, dust, and debris, or any foreign objects from entering your gas tank since these kinds of things can harm your engine.

gas cap

Serves As A Vacuum Seal

When the fuel is pressured, fuel may flow through it. Pressurized fuel is only achievable if the fuel cap is securely fastened to the fuel tank, creating a vacuum seal. This pressure helps the fuel pump collect fuel in the system efficiently.

Prevents Pollutants and Fumes From Escaping the Fuel Tank

It’s necessary to seal the fuel tank to ensure the proper operation of the evaporative emission control system (EVAP). The EVAP protects passengers and drivers from harmful gases (such as carbon monoxide) produced within the fuel tank. Additionally, the evaporative emission control system shields the atmosphere from contaminants released into the environment.

Avoids Fuel Contamination and Safeguards the Fuel Tank

If contaminants from outside penetrate the fuel tank, they may block the fuel lines, fuel filter, fuel pump, or even the fuel injectors. These contaminants will eventually render the vehicle’s engine inoperable. Moisture trapped within the gas tank can result in silt, corrosion, or rust.

Reasons Why the Check Fuel Cap Warning Light Comes On

When the dashboard’s Check Fuel Cap light glows, it may indicate something is wrong. These issues will cause the fuel cap to be incapable of performing its critical functions. The following are some probable reasons for the Check Fuel Cap light to turn on:

The Fuel Cap Is Missing

Fuel pressurization will not occur without a fuel cap. Without a fuel cap, the fuel tank will not be protected from contamination. The evaporative emissions control system cannot safeguard passengers and/or the environment from dangerous contaminants discharged from the fuel tank.

Several types of engine problems may occur due to a missing fuel cap on the tank. The Check Fuel Cap light will automatically come on if the fuel cap is missing.

The Fuel Cap Is Unsecured

One of the fuel cap’s functions is to maintain vacuum pressure. When the car’s gas tank has a loose cap, vacuum pressure will be released, resulting in vacuum leaks. The Check Fuel Cap light will glow with insufficient vacuum pressure due to a loose gas cap.

The Fuel Cap Is Excessively Tight

When the fuel cap is set excessively tight into the fuel tank, it may damage the fuel cap. The rubber or silicone seal on the fuel cap contributes to creating vacuum pressure, and squeezing the fuel cap too tight may cause the rubber seal to break or slide over, resulting in vacuum leaks.

The Fuel Cap Is Broken

A rubber or silicone seal and a gasket are located on the base of the fuel cap. If the rubber seal is gone or has shifted, or the gasket is damaged, vacuum leakage might occur. If the fuel cap is compromised in any manner, the Check Fuel Cap light will turn itself on.

Dirty Fuel Cap O-Ring

The fuel cap contains an O-ring, which is critical for your automobile to recognize whether the cap is on. Occasionally, this O-ring must be cleansed and oiled to alert the car’s system that the fuel cap is on.

Failing Check Fuel Cap Indicator

The electrical components in your car may be failing, and as a result, the Check Gas Cap indicator light might not come on. While this is an uncommon event, it does happen. Double check that this isn’t the case for you if you’re having engine issues. 

Signs and Symptoms of A Bad Fuel Cap

Because a bad gas cap may result in various mechanical issues, it’s crucial to be aware of the following indications that indicate the urgency for a gas cap replacement.

Issues on Tightening the Fuel Cap

The most obvious sign of a faulty gas cap is tightening and sealing issues. Vehicle makers design every gas cap to click immediately once sufficiently tightened. A damaged cap may not produce a clicking sound, which is a good indicator of replacing it. 

Foul Fuel Odour When Driving

If your car leaks fuel due to the inability of the gas cap to completely seal the tank, you may smell a foul fuel odor each time you get in the car. Not only does the leaking vapor cause driving your car more unpleasant by a fuel smell, but it also poses a serious health concern. Additionally, petrol is very flammable and may ignite when ignited by any form of fire.

Unusual Coloring Around the Lip of Fuel Tank

You most likely have a failing fuel cap if you see unusual deterioration or color around the fuel tank entry cover and the fuel filler neck. Due to the fuel cap’s inability to fully secure the tank, fuel vapors leak and accumulate on the fuel tank opening; these gases gradually stain the objects they come into contact with. As a result, you may detect a leaking fuel cap based on the fuel residue accumulated within your fuel tank filler tube opening.

Poor Fuel Economy

Besides protecting the environment from gas fumes, the fuel cap also saves you money by increasing the vehicle’s fuel efficiency. A leaky or cracked fuel cap harms your gas mileage. Without replacing it, you may waste up to 30 gal. of fuel every year.

Check Fuel Cap Warning Light

Another sign of a failed fuel cap is the Check Engine Light or the Check Fuel Cap warning coming on. The fuel cap is a critical component of the vehicle’s emissions system, so its ineffective fuel sealing can reduce efficiency. A fuel cap that cannot seal properly might result in an evaporative emission control system (EVAP) leak.

Fuel Cap Replacement Cost

If the fuel cap breaks, the car’s check engine or checks fuel cap light will activate when the system detects a fuel vapor release. Additionally, a malfunctioning fuel cap may raise fuel consumption and create a possible hazardous scenario if a spark ignites flammable vapors seeping from the car.

Every time we fill up, we touch the fuel cap. Examine yours the next time you fill your car. The cap is prone to damage and wear over time. When your fuel tank requires a new cap, the cost will range between $20 to $170. Of course, the price of a new gas cap is determined by the car’s make and model and the kind of fuel cap necessary for your car.


Besides securing the fuel tank, a car’s fuel cap serves various functions that help keep an automobile running correctly. A fuel cap sustains the vacuum pressure seal in the car’s fuel system, enabling the pump to properly deliver fuel to the combustion system.

Additionally, a fuel cap protects the environment by preventing dangerous contaminants and vapors from escaping the tank. The evaporative emission control system (EVAP) procedures protect vehicle occupants and the surrounding environment from the harmful effects of petrol fumes.

Finally, the fuel cap shields the fuel tank’s contents from external contaminants, dirt, dust, debris, and moisture during wet weather.


How long does a gas cap last?

Fuel caps are rated to last around 100,000 mi. or more. In rare instances, the gas cap may degrade rapidly due to excessively severe circumstances.

How can I shut the check fuel cap light off?

Do the following steps to deal with the circumstance:

  1. Exit the vehicle.
  2. Open the gas cap door.
  3. Inspect and secure the gas cap if required.
  4. Restart the engine and drive.

In a few days, the light should turn off. The code must be verified and examined by a qualified technician if the light stays on.

Is it safe to drive with a gas cap light warning on?

Yes, you can drive with the Fuel Cap Light on. Maybe you’re now questioning if you can drive safely with a missing gas cap. Technically, yes, you can also drive without the fuel cap. However, you should be aware of the potential issues this can cause with your car’s fuel and emissions components. If you must, you can drive until you reach home or a mechanic shop, but driving long distances without a gas cap is not recommended. 

How do I fix check fuel cap message?

You can fix the check fuel cap warning light by examining your fuel cap, ot looking at the seal or the o-ring to see if it’s still good. You can try cleaning off the o-ring and putting it back on the fuel tank’s lid with appropriate tightness. 

If the warning light doesn’t turn off after a few days, you should bring it to a qualified mechanic or technician to run it with their On board diagnostics (OBD-II code scanner) to find the fault in your car.

Sign up for our Newsletter

Related Articles