Is Your Check Engine Light On? What Is Wrong With This Picture?

Well you are driving along minding your own business and all of a sudden that little yellow light comes on. Yes that’s right your check engine light! There are many reasons why your check engine light can come on, but with today’s vehicles it is usually an issue with the evaporative emissions system. The first place to check is your gas cap, make sure it is tight turn tighten it until it clicks at least 3 times. Note the gasket on the aftermarket gas cap is sticking out. Always use an OEM replacement gas cap. You see fuel, or gasoline does not have to be burned to pollute the atmosphere. This is where the evaporative emission system comes into play; it basically controls the 

amount of fuel that evaporates  into the air. Any fuel vapor that is produced within the system is to be directed to and burned in the vehicles engine.

After market gas cap with bad seal

Note the gas cap pushing the gasket out of the way. this will definitely turn on the check engine light.

So what makes your check engine light come on when there is trouble with your evaporative emissions system? Well there are many components that make up your vehicles evaporative emissions system and it only takes one of them to fail to cause your check engine light to come on. Simply put your vehicles computer performs a self check of the emissions system. It uses the engines vacuum to check for leaks within the system. Typically the vent shut valve fails and the valve is usually located underneath the rear of the vehicle attached to a charcoal canister. What kind of work does this valve do? Just before the system check, vacuum is applied to the system. Then the vent shut valve is closed and the system is sealed tightly. If for any reason the system does not hold a vacuum for a specified amount of time, the system detects a fault and the check engine light will illuminate. The most common cause of evaporative emission system failure is a malfunctioning vent shut valve as indicated with the red arrow. The green arrow shows the charcoal canister,(see below) of which absorbs a lot of the fuel vapor produced within the system. Remember this if your check engine light comes on, do not panic. If your check engine light comes on and flashes continually this would indicate that you have a problem with a misfire issue. If this happens you need to turn off the vehicle as soon as possible to avoid catalytic converter damage, of which can be very pricy! If your check engine light comes on get it diagnosed and repaired as soon as possible.

Evaporative canister

Green arrow indicates the charcoal canister. The red arrow indicates the vent shut valve.

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