What Does the Check Fuel Cap Warning Light Mean? | How Do I Reset Gas Cap Light?

Your car dashboard contains multiple warning lights and symbols. Whenever something goes wrong, a light on your car dashboard starts illuminating. The check fuel cap light is more discreet than other warning lights. When driving a car, you must have an understanding of each car’s dashboard warning light meaning. This article mainly explains the check fuel cap light meaning, its causes, and how to fix it.

What Does the Check Fuel Cap Light Mean?

If your check fuel cap light is on, it indicates that your powertrain control module (PCM) detects a leak in your system, typically from a loose gas cap.

Check Fuel Cap Light

Your vehicle pumps fuel from the fuel tank into the combustion chamber where combustion process takes place. Your vehicle may also have evaporated fuel that is then collected and transferred to the engine where it is used.

The vaporized gasoline is captured in another tank known as the charcoal canister. As the specific operating conditions are met, the engine opens the valves, and the fuel vapors mix with the remaining burned fuel.

For the fuel system to work efficiently, it must be sealed from external air. A rubber O-ring is used in the gas cap to stop vapor from leaking when the cap is closed.

If the fuel cap light comes on while driving, park the vehicle in a safe place and replace the gas cap. With normal driving with the lights on, it should go away in a day or two. If the light stays on, check the gas cap for damage and change it if needed.

Function of the Fuel Cap

The fuel cap of your car performs the following functions:

Fuel Cap

  1. Vacuum Pressure Creation: Fuel can flow through the fuel system when pressurized. When the gas cap is securely fastened to the tank, a vacuum seal is created. This vacuum pressure allows the fuel pump to collect fuel in the system and run smoothly.
  2. Seals out contaminants and vapors in the fuel tank: The stoppage of the fuel tank leak is vital for the proper operation of the evaporative emission (EVAP) system. Your EVAP system prevents the driver and passengers from inhaling harmful gases generated in the fuel tank. Evaporative emission systems also protect the environment from pollutants that would otherwise be released into the atmosphere.
  3. Stops fuel contamination and guards fuel tanks: If external matter enters the fuel tank, it can clog the fuel pump, fuel injectors, fuel lines, or the fuel filter. This will eventually cause the vehicle’s engine to fail. Moisture in the fuel container may lead to container corrosion, rust, or deposits.

Causes why the Check Fuel Cap Warning Light Comes On

When the dashboard’s Check Fuel Cap light comes on, it means something is wrong. In such a condition, you must instantly find the root cause of the problem to prevent yourself from an expensive repair.

The following are the most common causes of the fuel cap light flashing:

  1. Missing Fuel Cap
  2. Unsecured Fuel Cap
  3. Excessively Tight Fuel Cap
  4. Damaged Fuel Cap
  5. Dirty Fuel Cap O-Ring
  6. Bad Check Fuel Cap Indicator

1) Missing Fuel Cap

Missing fuel cap

The missing fuel cap is one of the major causes of the check fuel cap warning light to come on. Without the gas cap, fuel pressure can’t be created. Contamination will be entered easily into your tank without a fuel cap.

In case of a missing fuel cap, the EVAP system of your vehicle can’t protect passengers or the atmosphere from harmful pollutants emitted from fuel tanks.

Various types of engine issues can take place without a fuel cap on your fuel tank. The check fuel cap light comes on automatically when the fuel cap is missing.

2) Unsecured Fuel Cap

loose Fuel Cap

One of the functions of the cap is to maintain vacuum pressure. When your fuel tank contains a loose cap, it releases the vacuum and creates a vacuum leak. If there is inadequate vacuum due to a loose cap, the fuel cap indicator light will illuminate.

3) Excessively Tight Fuel Cap

Overtightening the fuel cap on the fuel tank can damage the fuel cap. The silicone or rubber seals on the tank cap help to build up the vacuum pressure. Overtightening the gas cap can cause the rubber seal to crack or loosen, allowing the vacuum to escape.

4) Damaged Fuel Cap

Damaged Fuel Cap

The bottom of the gas cap is a rubber grommet and gasket. If the rubber seal falls off, loosens, or becomes damaged, it can cause a vacuum leak. The fuel cap indicator light comes on when the fuel cap is damaged.

5) Dirty Fuel Cap O-Ring

The O-ring is installed in the fuel cap to prevent leaks. This is important so that the car can detect if the gas cap is open. This O-ring needs to be cleaned and lubricated periodically to alert the vehicle’s system that the gas cap is on.

6) Bad Check Fuel Cap Indicator

The check gas cap warning light may not illuminate due to the failure of your car’s electrical parts. This is a rare occurrence, but it may happen. If you have problems with the engine, check if you are in this situation.

Read More: Symptoms and Causes of bad PCM

How to Reset the Fuel Cap Light

  1. First of all, Turn off the car engine. If your car has a locking fuel cap door, press the button to unlock the fuel cap door. It is typically mounted under the steering column or on the floorboard next to the driver’s seat.
  2. Go to the fuel cap door.
  3. Now open the fuel cap door. Hold the handle located on the fuel cap and turn counterclockwise to loosen the fuel cap. In this way, your fuel cap will be removed.
  4. Install the new cap. Removing and reinstalling it will seal the threads properly if they weren’t properly sealed before. Tighten the gas cap by turning it clockwise. Keep turning until you hear three clicks. This will ensure a correct fit.
  5. After installing the new cap on the fuel tank, return to your cabin, start the engine and drive the car for a few hours. The OBD-II scanner will automatically reset the “Check Engine” or “Loose Cap
  6. If the warning light persists, utilize the OBD-II code scanner. Plugs into the OBD-II port under the steering column. This port is the same as the printer port on your computer. Press the reset button on the code scanner to clear the system.
  7. Now start driving your car. Keep an eye on your dashboard warning light to make sure it doesn’t light up again. If so, the fuel cap may be defective. Visit your auto parts store or dealer service to buy a new fuel cap.

Fuel Cap Replacement Cost

The replacement cost of the gas cap varies according to your vehicle model, labor cost, and your living area. The average replacement cost of the fuel cap is from $90 to $105.

FAQ Section

Why does my car keep saying check fuel cap?

The fuel cap light shows that your PCM/ECM notices a leak in your fuel system, usually caused by a loose gas cap. If this light starts illuminating while driving, park the car in a safe place and replace or re-secure the fuel cap.

How do I know if my fuel cap is bad?

The following are the most common symptoms of a bad fuel cap:

  1. The fuel cap is not tightening completely
  2. Loose cap
  3. Check fuel cap light illumination
  4. Poor engine performance
  5. Various Emissions related Error Codes
  6. Poor fuel economy

How do I fix the check fuel cap message?

A gas cap warning light can be fixed by inspecting the O-ring, fuel cap gasket, or gas cap to check if it is still good. Cleaning the O-ring, reinstalling it back on the gas cap, and tightening it properly may also fix the check fuel cap message. If the warning light doesn’t go off after a few days, take it to a professional to run onboard diagnostics (OBD-II code scanner) to find out what’s wrong with your vehicle.

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

It is not recommended to drive with the check gas cap message, but still, you can drive. You may want to ask if driving without a gas cap is safe. Technically yes, you may continue driving without a gas cap. However, be aware that this can badly damage your vehicle’s exhaust and fuel components. You can drive to your house or garage if you wish, but driving with a missing gas cap isn’t recommended for long periods.

What happens if you don't tighten the gas cap?

If you don’t tighten the fuel cap, your Check Engine Light may start to illuminate. This is a major cause of the check engine light illumination. If the gas cap is loose, your fuel vapor can escape.

Why is my check engine light still on after replacing the gas cap?

Even a new air cap may not seal properly if it is unusually worn or damaged. Even if the check engine light does not come on or there is a leak in the EVAP system, there may be a leak or malfunction in the EVAP system.

Is it hard to replace a gas cap?

Installing a new gas cap is a very simple process, but the exact steps may vary depending on the type of gas cap you have. Before installing the new cap, you should also know how to remove the old cap. Follow the manufacturer’s instructions to replace your gas cap.

How long does a gas cap last?

A gas cap typically lasts about 50,000 miles, but you should replace it sooner if it gets damaged.

Can I drive with a broken fuel cap?

Driving without a gas cap doesn’t damage the engine. However, it is not recommended to drive. You will not waste fuel by driving without a gas cap because your car has a butterfly valve that prevents fuel from going out of the tank.

Read More
  1. Causes and Symptoms of a bad PCM
  2. Car Dashboard Warning Lights and Symbols
  3. Bad MAF Sensor Symptoms and Causes

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