How To Test an EVAP Purge Valve (No Tools Needed)

By | December 22, 2023


The purge valve is a common failure in an EVAP system which often needs to be tested to see if it has gone bad.

There are several ways to test the purge valve, including using a multimeter, vacuum pump, or a quick method that requires no tools.

While using a multimeter or vacuum pump are good options, there is also a way to test the purge valve with no tools needed.

What is the EVAP Purge Valve?

The purge valve is a component in a vehicle’s EVAP system for emissions.

An EVAP system contains the gas vapors and sends them into the engine to get burnt off.

The purge valve opens to let gas vapors into an engine when it is running and closes when the engine is off.

Can the Purge Valve be Tested Without a Multimeter or Vacuum Pump?

Yes, there is a method to see if the purge valve opens or closes by feeling for a vacuum.

The purge valve solenoid is opened and shut by the vehicles computer depending if the engine is cold or warmed up.

When the engine is off or cold, the purge valve stays shut.

When the engine is hot, the purge valve opens up and sends gas vapors to the engine to be burnt off.

The line going to the charcoal canister is removed and felt to see if there is a vacuum or not at the correct time.

Since the valve stays shut when the engine is cold, no vacuum should be felt at the port.

Since the valve opens when the engine is hot, a vacuum should be felt at the port after the engine warms up.

There can be some differences between manufacturers when the computer tells the valve to open, but it will at some point.

How To Test a Purge Valve With No Tools

  1. Disconnect the hose coming from the Charcoal Canister.
  2. Start the engine and feel at the port if there is a vacuum.
  3. The valve should be closed, when the engine is cold, with no vacuum.
  4. If there is a vacuum at the port while the engine is cold the purge valve is bad.
  5. Wait for the engine to warm up and feel at the port again if there is a vacuum.
  6. The valve should open when the engine is hot, and there should be a vacuum at the port.

Can a Purge Valve Be Tested Without a Multimeter?

Yes, a purge valve can be tested without a multimeter.

During the cycle of the Evap system, of the engine warming up, the valve can be checked to see if it is open or closed.

Can a Purge Valve Be Tested Without a Vacuum Pump?

Yes, a purge valve can be tested without a Vacuum Pump.

The onboard computer keeps the valve closed when the engine is cold and then opens it up when the engine is hot.

Removing the line from the charcoal canister and checking for a vacuum by touching the port will show if the valve is working or not.

Bob Thomas

2 thoughts on “How To Test an EVAP Purge Valve (No Tools Needed)

  1. LS

    Hello! I have a 2003 slk32 AMG and recently had the check engine light come on. I took it to Auto Zone to check for a code which turned out to be PO444 and according to Auto Zone it was possibly “The purge valve of the Emission Control System has an open circuit”. I checked the valve per your instructions – left it plugged in – removed the hose from the canister side – started the car and after warm up it DID have a vacuum. So my questions are 1) Could the valve still be bad and this is an intermittant issue? 2) if not, what else could that code mean?

    As a side note I have noticed periodically there is a strong smell of gas under the hood with no apparent visible leak of gas what so ever i.e fuel lines and around the site of the injectors. It is stronger on the drivers side than passengers.

    The only other thing to mention is occasionally the car seems to shutter some when coming to quick stop.

    Any thoughts would be greatly appreciated!!!

    Thank you!
    LS

    Reply
    1. Don

      Did the purge valve have a vacuum when the engine was cold? If so, it is stuck open. It should only open after the engine has warmed up and the computer sends a signal for the valve to open.

      Reply

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