What Is a Canister Purge Solenoid?
You’ve probably noticed that fuel gives off a pretty strong smell. That’s because it’s evaporating, creating pollution and health problems as it disperses throughout the atmosphere. Luckily, manufacturers have developed the EVAP (Evaporative Emission Control) system to solve this problem. There are several components at work in this system, and when they fail, it can cause problems for your car, your health and the environment. The canister purge valve is an integral component of the EVAP system, but also one that is subject to failure over time. What is a canister purge solenoid, and how can it make or break an EVAP system?
The “evaporative emission” in EVAP refers to the vapors that naturally occur when fuel meets air. They contain hydrocarbons, which cause smog pollution and have serious negative health effects on humans. Since most engines require fuel to run and that fuel must be stored somewhere, vapors are released 24/7, even when the car is off. And it’s not as simple as containing them in a completely closed system, because when they expand (especially when they’re hot), they can escape or damage other engine components.
So what is a canister purge solenoid, and how is it related to these potentially destructive vapors? Well, with all these limitations in mind, manufacturers install an EVAP system to collect and store the vapors in a canister purge solenoid until the engine is started again and they can be released and burned through normal combustion. The canister operates via either a vacuum or electricity and is filled with charcoal, which traps the vapors. Most modern vehicles have electronic canister purge solenoids controlled by the engine control unit, or ECU. After the car is started, the computer waits for the engine to reach operating temperature, then sends a signal to the solenoid on top of the canister to open the valve, letting the stored vapors into the combustion system.
Heart and Solenoid
While the charcoal in the canister should last throughout the vehicle’s lifetime, the solenoid itself might not. Most often, these fail because they’re stuck open or closed. If this happens, you may notice a few telltale signs. For one, your check engine light will illuminate. Emissions are closely monitored in modern cars, so if there’s a leak somewhere, your ECU will alert you. Because combustion relies on these vapors for top performance, your mileage will suffer if they aren’t released into the engine. A stuck-open valve creates a vacuum leak that allows too much air to enter the engine, throwing off the air-fuel ratio and causing a noticeably rough idle or hard start. And if you fail an emissions inspection, a faulty solenoid may be to blame.
If you suspect your canister purge solenoid is broken, check it by applying a vacuum or voltage to the solenoid to see if it opens. Also, be sure to check its resistance to see if the problem is an electrical open or short circuit. Luckily, if the purge solenoid is found to be at fault, it’s a pretty easy fix.
Check out all the fuel and emissions products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on canister purge solenoids, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.
Photos courtesy of Blair Lampe.