The gas cap, or the fuel filler cap, is an essential component of your car. It prevents debris, dirt, and dust from entering the gas tank and provides a reliable seal. It also plays a substantial role in converting dangerous fuel vapor into harmless discharge in the vehicle’s emission system.
You are most likely to have a loose gas cap or a worn-out one after some time because you have to remove it for every fueling session. Loose gas caps can lead to several problems, including fuel leakage problems resulting in uncomfortable smells and hazardous effects to you and your car.
If your check engine light turns on, but you do not notice any problem with your engine, you might be having a loose gas cap. While the problem requires a minor fix, ignoring it can lead to more severe issues, requiring plenty of money and time to fix.
Here are some problems that a loose gas cap can cause to you and your car:
Is a Loose Gas Cap Dangerous?
A fuel tank gas cap plays a significant role in your car’s evaporative emission system. If you establish that your gas cap is loose and requires tightening, you should do that to prevent it from causing any problems. However, a loose cap can indicate several serious issues that might need your attention.
Here are some signs that should prompt you to check on the condition of your gas cap:
Can a Loose Gas Cap Trigger the Check Engine Light?
Several reasons, including a loose gas cap, can prompt the “check engine light” to turn on in your vehicle. Your vehicle’s gas cap plays a significant role in the car’s evaporative emission system; therefore, if it’s broken or loose, it can create an Evaporative Emission Control System (EVAP) leak. This leak causes the check engine light to turn on as soon as your car’s computer detects the leak.
If the Gas Cap Does Not Tighten or Click as It Should
Your gas cap should click if it’s appropriately tightened. You may have to replace your gas cap if it does not click or clicks but pops loose after some time.
Fuel Smells Coming From Your Vehicle
Fuel smells coming from your vehicle may be due to a worn-out or damaged gas cap seal that causes fuel vapors from the gas tank to leak from the filler tank. The fuel smells are a result of the vapors escaping from the leak.
Check this too: How to Prime a Mechanical Fuel Pump
Can a Bad Gas Cap Cause Low Fuel Pressure?
When your vehicle has a failing or bad gas cap, it will set out a P0455 or a P0457 code to the car’s engine control module. These codes often mean that your vehicle has a loose gas cap problem or a massive leak.
The two codes might also mean insufficient pressure in the fuel injection system due to the damaged or faulty gas cap. So while the loose cap doesn’t necessarily lead to low fuel pressure, your car’s ECU can throw the same error for the two problems.
How to Reset Check Engine Light after a Loose Gas Cap
The good thing about modern cars is that they have an automotive diagnostic system known as an onboard diagnostics system (OBD-II). This system is efficient because it monitors several engine and emissions-related components to confirm that everything is working well.
A “Check Engine” warning light turns on if your gas cap is loose or not correctly attached. You can choose to tighten the cap or wait for the system to reset itself after it determines that the problem has been fixed. You can also use an OBD-II scanner to reset the system manually by following these steps:
- Turn off your car’s engine, and then push the button that unlocks the gas cap door if your vehicle has a locking gas cap door. You will mostly find this door beneath the steering column or on the floorboard next to the driver’s seat.
- Go to the gas cap door, open the door, hold the gas cap handle, twist it counterclockwise to unscrew it, and then remove it.
- Replace the gas cap to ensure the thread seals properly if it hadn’t before. Turn it clockwise to tighten it. It would help if you turned it until you hear it click thrice because this ensures that it’s seating properly.
- Close the gas cap door and head over to the driver’s seat. Drive your car for at least a day, and the OBD-II system will automatically reset the “Check Engine” light.
- If the warning light does not disappear after a day, use an OBD II scanner. Connect the scanner to the OBD-II port that’s located beneath the steering column. The port resembles a computer printer port. Push the “reset” button on the code scanner to clear the system.
- Drive your car and pay attention to the warning light. If it comes back on, you might have a faulty gas cap. Make necessary arrangements to have it replaced.
Can a Bad Gas Cap Cause Idle Problems?
Most fuel-injected cars use pressurized fuel systems and rely on the tightness of the gas cap for the required pressure. A failing or loose gas cap may bring idling problems due to insufficient fuel system pressure.
Additionally, the idle problems can be due to impurities and dirt that get into the gas tank’s neck because of a faulty gas cap. The impurities alter the fuel injection pressure and block or clog the featured fuel delivery causing rough idling.
Can a Loose Gas Cap Cause Stalling and Misfires?
Your car may misfire or stall if the required fuel combustion doesn’t happen. Insufficient combustion occurs when your air to fuel ratio is not at the recommended levels. If you have a damaged gas cap, you might experience a fuel leak outside the pipes and tanks.
A faulty gas cap can cause misfires and stalling. However, the most common causes for vehicle misfires and stalling include ignition problems, a bad fuel pump, electrical transmission issues, or a faulty air flow sensor.
Can a Bad Gas Cap Cause Hard Starting?
A faulty gas cap can trigger the “Check Engine” light; however, it will not usually cause car performance issues. Lack of sound and shaking from the fuel pump may indicate that the fuel pump is failing, or the fuel pump relay may not be sending power to the fuel pump leading to the engine having less fuel. When this happens, a car can experience difficulty when starting.
Check this too: What Are The Signs Of A Weak Fuel Pump?
How to Fix a Loose Gas Cap
Fixing a loose gas cap is not a complicated procedure. You can fix it by following the process below:
- Open the fuel tank door by pushing a button located next to the driver’s seat or near the glove compartment box.
- Open the tank door physically and check the gas cap carefully to determine if it has any physical damages.
- If you do not find any damages, screw the gas cap to the tank, and ensure it clicks. Clicking symbolizes that it’s completely tightened.
How to Test Gas Cap Pressure
If your car has sent a bad gas cap code, but you don’t find any physical evidence of the leakages after close inspection, you might need to test gas cap pressure. Pressure testing can help you rule out any leakages in the deeper parts of the fuel system.
You can do pressure testing by following these steps:
- Use needle and nose vise grips to cover the inlets and outlets of the tank.
- Use a pressure tester and establish any pressure changes within five minutes of sealing the tank’s inlet and outlet.
- You can also use a smoke machine with low-pressure oil and colored dye to confirm any leaks. When you pump the Evaporative Emission Control System (EVAP) with the colored dye, you will identify the location of the leakages.
A gas cap performs various roles to ensure that your vehicle runs smoothly. Always ensure that your car’s gas cap is not faulty, loose, and dirty to prevent your vehicle from experiencing clogging, which might spoil the fuel filter, pump tank, and injection systems. If you do not take care of these problems, your engine might malfunction eventually.