6 Common Bad Purge Valve Symptoms

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Purge valves, or canister purge valves, are an integral part of the EVAP system in every motor vehicle. A purge valve, as the name implies, helps to “purge” the EVAP system by allowing vapor into the engine. If the purge valve fails, the EVAP system will malfunction because it is no longer “purged” (cleaned).

A bad purge valve would trigger different unusual signs and affect your car’s emissions output levels.

That said, it is important to be aware of the common bad purge valve symptoms so that you’d know and take appropriate actions when they occur. The purge valve can be entirely replaced if it’s severely damaged.

Below are the various signs of a bad purge valve you should know about!

Common Bad Purge Valve Symptoms

1. Rough Idle

Rough idling is a state of inconsistent speed levels while your car is idling. Although there are many problems that could lead to road idling, a bad purge valve is one of those problems.

So, when you stop your car and notice that it is idling roughly – maybe little shakes as you try to move forward – that’s a sign to check on the purge valve and other possible causes.

2. Poor Fuel Economy

If the valve is stuck open, it allows fuel vapors to escape and also causes the engine to use more fuel, which would result in poor fuel economy.

Usually, modern ICE vehicles utilize fuel vapors mixed with air for combustion, so if anything interrupts this process, combustion processes won’t carry on smoothly, and that could lead to poor fuel economy.

3. Your Car Won’t Pass Emissions Tests

A bad purge valve could be the reason why your vehicle won’t pass emissions tests. How is that possible?

The purge valve is part of the Evaporative Emission Control (EVAP) system; this system restricts fuel vapors in the fuel tank from escaping – rather traps the vapors in a charcoal canister and releases them into the engine like regular fuel.

Now, the flow of those vapors is controlled by the purge valve, which is electrically controlled. So, if the valve is faulty, it could prevent your car from passing emissions tests.

That said, if your car wouldn’t pass your state’s emissions tests while the exhaust and its components look all good, then you should troubleshoot the EVAP system; the purge valve may have gone bad.

4. Check Engine Light Stays On

While there are many reasons for the check engine light to appear on your car’s dashboard, a faulty canister purge valve can be of those reasons. That said, when the check engine icon illuminates, the first thing is to troubleshoot the vehicle and see what triggered the light.

If your troubleshooting device showed DTCs like P0441 and P0446, the problem is with your car’s EVAP system, and there are chances it could be a malfunctioning or failed purge valve.  

5. Poor Engine Performance

One of the things a faulty purge valve would cause is that it’d significantly reduce how your car’s engine performs. The engine would be sluggish, use more fuel, and probably won’t accelerate smoothly. When you start noticing several uncommon engine faults, it’s time to check on the purge valve.

6. Difficult Starting

The majority of a canister purge valve’s work is done when you want to start the engine after you have turned it off prior.

So, if the valve is bad (stuck open), an excess amount of air would penetrate into the combustion chamber, thus affecting the air-fuel ratio; while this scenario can’t possibly stop your car from starting, it may delay the cranking time – so you just have to try a little more harder to start your car.

What Makes a Purge Valve Go Bad?

There are a number of reasons why auto valves go bad. However, the most common reasons include dirty build inside the assembly, clog, faulty wiring or connection, and malfunctioning ECU.

In other words, sometimes, when you’re faced with a purge valve failure scenario, it’s important to also check the aforementioned reasons that could have caused the valve’s failure.

Frequently Asked Questions

Can You Drive With a Bad Purge Valve?

Apparently, a bad purge valve won’t stop your car’s engine from starting – it can only cause a delay. Having said that, it is very much possible to drive with a faulty purge valve. However, you should try fixing it as soon as possible before it leads to other problems.

How Much Does It Cost To Fix a Bad Purge Valve?

Fixing or replacing a bad purge valve is one of the inexpensive, affordable repairs you can do on a car. The average cost of replacing purge valves is between $100 – $200, depending on your car’s model and make, and also, the reason why the valve is damaged; if the valve got damaged due to faulty connections, you’d need to fix the wrong connections, and that’d cost some money too.

What Happens When A Purge Valve Goes Bad?

When a purge valve is bad, trapped fuel vapors won’t be able to get into the engine or may flow to the engine in excess, causing the engine to run on low fuel or too much fuel, which is not good. You’d notice that your car overheats, rough idles, and the check engine light stays on when you’ve got a bad purge valve.


This article explains the common bad purge valve symptoms experienced by most drivers. The best solution to fixing a faulty purge valve is to replace it, which costs around $150 on average.

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