Three Common Causes of This Check Engine Light Warning OR How Car Rental Agencies Encourage You to Damage Their Vehicles

Nov 21, 2023

The Purpose of The EVAP System

In short, the purpose of the EVAP system is to control and prevent the release of gasoline vapors from gasoline inside your tank and escaping into the atmosphere and adding to the environmental smog problem we see in congested traffic.

The primary component in the EVAP system is an external charcoal canister that traps the vapors until the engine's ECM directs the control and refinement of the vapors involving several other key components that includes a fuel check valve inside the tank fuel pump, a fuel temperature sensor, pressure sensor(s), vent(s), purge solenoids, vacuum hoses, the tank filler neck, and last but not least…the gas cap.

These gas vapors are eventually routed to the intake manifold where they are burned off unless something causes the EVAP system to fail such as a vacuum leak in the hose or connectors, a failure of the pumps/solenoids, or damage to the charcoal in its cannister.

Learning a Little Something about Your EVAP

In an earlier article we learned how that a fake Toyota gas cap delayed the repair of a vehicle with an EVAP problem and how this is one of the first (and simplest) things you can check if your vehicle indicates an EVAP-related problem.

In today's article, we are going a little more in depth about the EVAP system that begins with an excellent video as one is dismantled from a car to show the isolated components in connection to each other along with an explanation of what each component in the system does.

This is then followed by a second video that supports what you’ve learned in the first video and focuses on 3 components commonly associated with an EVAP failure-generated check engine light warning.

And finally, the reason why car renters intentionally (or not) damage the EVAC systems on rental cars.

How the EVAP System and Gas Tank Work

Check Engine Light? Codes P0446, P0455: What Causes a Car EVAP Code?

And finally…

I do not particularly care for car rental agencies…too many bad experiences that many of us can identify with. However, one of my biggest complaints is the practice of a rental agency attempting to gouge me the cost of a full tank of gas at THEIR gas price, despite the fact I filled the tank prior to returning the vehicle.

I’ve experienced rental representatives who told me that I owned them charges for a full tank of gas because the fuel needle (or digital equivalent) was on the low-side of the full mark! Apparently somehow there are degrees of where the needle and full tank mark touch that is an issue with some of them.

My solution---and I’m willing to bet many of us do it---is to overfill rentals just to ensure that I am not dinged for a less-than-absolutely full tank when returning a car.

In case you missed the message in the videos, there's a reason why you stop fueling when the service station fuel pump automatically kicks off and why you should not force the nozzle to "top-off" the tank---you risk liquid gas making its way to the charcoal cannister and damaging it. It's as simple as that. And, another good reason why not to buy a used car from a rental agency.

For additional articles related to car rentals, here are a few for your consideration:

• Car Renters Risk Arrest Because of This Rental Agency's Policies

• How Car Rental Companies Scam People Out of Money

• Do Not Buy a Used Rental Car for This Reason

Timothy Boyer is Torque News automotive reporter based in Cincinnati. Experienced with early car restorations, he regularly restores older vehicles with engine modifications for improved performance. Follow Tim on Twitter at @TimBoyerWrites for daily new and used vehicle news.

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