Q: What does it mean if the Check Fuel Cap message is displayed?

A common misconception is that the only purpose of a fuel cap is for it to be a top for the fuel tank. It actually has many purposes and is a critical component of the evaporative emissions (EVAP) system. If the fuel cap is not affixed to the fuel tank properly, or is damaged, this may cause problems with the efficiency of the engine, problems with the evaporative emissions (EVAP) system, a decrease of gas mileage, and/or fuel leaks.

• A fuel cap creates vacuum pressure seal. Fuel is able to flow through the fuel system when it is pressurized. Pressurized fuel is able to be achieved when the fuel cap is tightly secured to the fuel tank, creating a vacuum seal. This pressurization enables the fuel pump to gather gasoline in the system to operate smoothly.

• A fuel cap seals pollutants and fumes inside the fuel tank. Sealing the fuel tank is important for the evaporative emissions (EVAP) system to function properly. The evaporative emissions (EVAP) system protects drivers and passengers from inhaling the dangerous fumes that are created inside the fuel tank. The evaporative emissions (EVAP) system also protects the atmosphere from the pollutants that would otherwise be expelled into the environment.

• A fuel cap prevents fuel contamination and protects the fuel tank. If outside contaminants get into the fuel tank, this may cause clogging of the fuel filter, fuel lines, fuel injectors, or the fuel pump itself. This will ultimately prevent the vehicle’s engine from working. Moisture inside the gas tank can cause sediment, rust, or corrosion inside the fuel tank.

When the Check Fuel Cap Light comes on in the dashboard, this may indicate that the fuel cap has not been affixed onto the fuel tank filler tube properly, the fuel cap is missing from the fuel tank filler tube, or that the fuel cap is damaged in some way. These issues will prevent the fuel cap from serving one or more of its many vital purposes. Here are some possible causes for the Check Fuel Cap Light to come on:

• Missing fuel cap.If the fuel cap is not on the fuel tank at all the fuel can not be pressurized, the fuel and fuel tank can not be protected from contamination, and the evaporative emissions (EVAP) system can not protect passengers and/or the atmosphere from the harmful pollutants that are emitted from the fuel tank. There is a multitude of damage to the engine that can be caused by not having a fuel cap on the fuel tank. The Check Fuel Cap Light will be displayed if the fuel cap is missing.

• The fuel cap is loose. One of the purposes of the fuel cap is to hold vacuum pressure. If the fuel cap is not tightly secured to the fuel tank, this will cause a loss of vacuum pressure and vacuum leaks. When there is improper vacuum pressure and/or vacuum leaks, the Check Fuel Cap Light will be displayed.

• The fuel cap is too tight. If the fuel cap is screwed onto the fuel tank too tightly, it could damage the fuel cap itself. The fuel cap’s rubber seal helps to create vacuum pressure, and putting the fuel cap on too tightly can cause this rubber seal to roll over and will cause vacuum leaks. If the fuel cap is too tight, the Check Fuel Cap Light will be displayed.

• The fuel cap is damaged. On the underside of the fuel cap is a rubber seal, and a gasket. If the rubber seal has rolled over, the rubber seal has been removed, or the gasket is broken this can cause vacuum leaks. The Check Fuel Cap Light will be displayed if the fuel cap is damaged in any way.

If your Check Fuel Cap Light is on, it would be a good idea to have this issue inspected and diagnosed as soon as possible.