What Are The Symptoms of a Bad Purge Valve? . A hard starting, rough idling, and decreased fuel efficiency – these are just some of the telltale signs of a failing purge valve. This essential component of your car’s emissions system plays a crucial role in engine performance, and when it malfunctions, it can lead to a range of frustrating problems. Let’s learn about the symptoms of a bad purge valve to get timely methods.
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What Is A Purge Valve?
The car purge valve, also known as a canister purge valve, is a component of the evaporative emissions control (EVAP) system in modern vehicles. The EVAP system is designed to capture and store fuel vapor emissions from the fuel tank and prevent them from escaping into the atmosphere. The purge valve is responsible for regulating the flow of fuel vapor from the EVAP canister to the engine intake manifold.
When the engine is running, the purge valve opens and allows the fuel vapor to be drawn into the engine and burned along with the fuel/air mixture. This helps to reduce emissions and improve fuel efficiency. The purge valve is controlled by the engine control module (ECM) and is typically located near the EVAP canister or on the intake manifold.
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It is usually a small, solenoid-operated valve that opens and closes based on signals from the ECM. If the purge valve fails or malfunctions, it can cause a variety of issues, including rough idling, stalling, and poor fuel efficiency. In some cases, a malfunctioning purge valve can also trigger the check engine light to come on. If you suspect a problem with your car’s purge valve, it’s best to have it diagnosed and repaired by a qualified mechanic.
Symptoms of a Bad Purge Valve
When the purge solenoid valve gets stuck open or closed, your vehicle will experience one or more of the following symptoms:
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Active Check Engine Light
An active Check Engine Light is one of the most evident signs of a bad purge valve. When the ECU detects less or excess fuel vapour being released by the valve, it activates the engine light and registers related DTC trouble codes.
However, the engine light is the most ambiguous warning light on your dash. You’ll need to consult a mechanic to diagnose and confirm if a bad purge valve is triggering the Check Engine Light.
Rough Idling
When a bad purge valve is stuck open, it can lead to an EVAP leak (vacuum leak). This affects the air-fuel ratio during combustion, causing a rough idle. Sometimes, an EVAP leak could also result from a damaged purge valve solenoid or the vacuum hose attached to it. If ignored, a vacuum leak could cause an engine to stall completely.
Difficulty Starting
Like a rough idle, a faulty canister purge valve can make starting your car difficult. This is due to the vacuum leak created by a stuck open purge solenoid valve. The leak leads to more air inside the combustion chamber than required, compromising the combustion process.
Poor Engine Performance
Even if your vehicle manages to start with a faulty purge valve, you may experience poor engine performance down the road. Your engine will fail to generate enough power while you accelerate.
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Poor Gas Mileage and Fuel Economy
Since a malfunctioning purge valve can affect the air-fuel ratio for combustion, it’ll also adversely affect your gas mileage and fuel efficiency.
If the valve is stuck closed, the gasoline vapor directed by the purge valve to the combustion chamber will end up being vented out through the EVAP canister instead. This will lead to gas wastage and affect your fuel economy.
Failed Emissions Test
As mentioned earlier, the canister purge valve is a part of the Emission Control system. It ensures that your vehicle meets the emission standards by preventing harmful hydrocarbons in the gas vapor from leaking out. So, when a faulty valve fails to do its job, you’re most likely to fail an emissions test. You might also notice excessive black smoke from the exhaust, which translates to increased emissions.
Collapsed Fuel Tank
A fully open purge valve can sometimes make the fuel tank (gas tank) collapse and deform.
Though rare, this can happen if the purge valve is stuck open while the EVAP canister vent valve is shut, creating an excessive vacuum in the EVAP system. This can also trigger the P0457 code for an EVAP leak due to a loose or missing gas cap.
Fuel Smell from the Engine
If you can smell gasoline vapor from your engine, chances are your EVAP purge valve isn’t closing correctly, causing the fuel vapor to leak out.
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What Causes the Purge Valve to Go Bad?
Here are some of the possible causes of a failing purge valve:
- Faulty Purge Valve Solenoid: Did you know the EVAP purge valve and the purge valve solenoid are two different parts? The solenoid is an electromagnet responsible for opening and closing the purge valve. So, a faulty solenoid could affect the functioning of the vapor canister purge valve.
- Faulty Wiring or Faulty Connectors: Any loose or damaged wiring to the canister purge solenoid could cause it to malfunction. Likewise, dirty or corroded connectors can lead to a faulty canister purge valve.
- Dirt Build-up: Fuel deposits, dirt, or normal wear from frequent use could block the purge valve and affect its functioning.
- Leaks from the Purge Valve: If fuel vapors leak from the valve, it won’t be able to maintain the fuel tank pressure, which will also be noted by the fuel tank pressure sensor.
- Faulty Engine Control Unit (ECU): Since the ECU (your car’s computer) electronically controls the purge valve through the solenoid, a malfunctioning ECU can affect its functioning.
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How to Test the Purge Valve?
To test the vapor canister purge valve, you need to locate it first.
It’s a small plastic component found in the engine compartment on a hose running from the intake manifold to the canister. On some vehicles, it’s located near the fuel tank. Check your owner’s manual to find its exact location.
Here are the steps to test it:
- Let the engine cool down and disconnect the battery.
- Inspect the car’s purge valve and its hoses for visible signs of damage. Replace any damaged components.
- Next, use a multimeter to measure resistance across the valve’s terminals. Compare it to the specified value (usually 20-30 ohms).
- Reconnect the valve, turn the ignition “ON,” and listen for a clicking or humming sound. No sound may indicate a problem.
- Optionally, use a vacuum tester to apply the vacuum to one end of the valve. Once the vacuum tester builds enough pressure, the valve should open and allow air to flow through.
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FAQs about the Purge Valve
1. What Is a Purge Valve?
The purge valve, also called the vapor canister purge valve, is a critical part of the EVAP system. The system prevents fuel vapors in the gas tank from being released into the atmosphere by trapping them in the charcoal canister. The vapors sit in the charcoal canister until they are needed again.
When the car’s engine runs, these vapors are released back to be burned along with the fuel. Your canister purge valve controls the flow of these fuel vapors. This valve is electronically controlled by the ECU via a purge valve solenoid.
2. Can You Drive with a Defective Purge Valve?
While you can continue driving with a faulty canister purge valve, you shouldn’t ignore the symptoms for too long. A failing purge valve will cause increased emissions and adversely affect the environment.
Secondly, the valve will continue to suffer damage and affect the charcoal canister and other critical engine parts like the catalytic converter. Such parts can be expensive to replace.
3. What DTC Codes Result from a Bad Purge Valve?
A malfunctioning purge valve will cause the car’s computer to activate the engine light and register one of the following trouble codes:
- P0443 – Evaporative Emission Control System Purge Control Valve Circuit
- P0444 – Evaporative Emission Control System Purge Control Valve Circuit Open
- P0445 – Evaporative Emission Control System Purge Control Valve Circuit Shorted
- P0446 – Evaporative Emission Control System Vent Control Circuit
- P0455 – Evaporative Emission Control System Leak Detected (Large Leak)
- P0456 – Evaporative Emission Control System Leak Detected (Small Leak)
- P0457 – Evaporative Emission System Leak Detected (Fuel Cap Loose/Off)
- P1443 – Evaporative Emission Control System Control Valve
4. What Is the Purge Valve Replacement Cost?
Generally, replacing a purge valve costs $110 to $170. The part costs around $75-$110, and the labor charges can vary from $40-$55.
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