What is an Evaporative Emissions Leak? Tempe Arizona

Right at the top of the list of codes that we see on cars coming in to the shop here at All Tune and Lube Total Car Care in Tempe are those related to evaporative emissions leaks. These are the faults you hear about that can be as simple as a loose or bad gas cap, but they can indicate more serious problems too.

An EVAP leak code indicates a fault that is permitting gasoline vapor to escape. The first question we’re asked when these codes show up is “Is it safe to drive my car?” and the short answer is sure, but you want to get it taken care of as soon as you can. The Evaporative Emissions System (EVAP for short) is a pollution control system and doesn’t affect drivability, safety or fuel economy. What it does is help keep fuel vapor out of the air we breathe.

The fuel system on a modern car is sealed so that vapor can’t just willy nilly escape in to the atmosphere. There are a couple systems that work together to allow the fuel tank to vent, but trap the vapor produced by gasoline and run it back through the engine. The most important and most easily replaced part of this system is the fuel cap. It’s not hard to tell why. I mean, right there is a big ol’ hole leading right down to the fuel tank. Without a cap that seals properly, nothing else in the EVAP system works.

The other major components are the vapor canister, purge control solenoid and flow sensor. These work together to collect fuel vapor and send it back to the engine intake when conditions permit. The fuel tank, vapor canister, purge control and flow detector are connected by various lines or hoses.

On the whole, the EVAP system is pretty robust, doesn’t require any maintenance (though some manufacturers recommend replacing the charcoal canister from time to time) and doesn’t give much trouble. When trouble does occur the codes that show up most often are the P0440 Large EVAP Leak (That’s the one most likely to be a fuel cap) or something like a P0443 Purge Valve Fault. Sometimes we’ll see a P0442 Small EVAP Leak which can be a bear to locate and repair.

Anyway, I hope you found this useful and if you do have EVAP issues you’ll remember us. Your Local Mechanic, All Tune and Lube Total Car Care Tempe Arizona.