How to Fix an EVAP Leak

In this article a GM truck is used.

Nine times out of ten when this code is set the system has a problem it is because of a leak somewhere between the intake manifold and the vacuum control solenoid. This could be a loose or faulty vacuum feed line because of a worn O ring seal or a hose that has falling off or has a tear.

If these items check out okay either the purge or vacuum control solenoids is having a problem. Let’s go over the system step by step so you can have a better understanding of how the system works and how easy it is to fix it.

When a check engine light or service engine soon light comes on it could indicate an EVAP system problem, you must read the trouble codes to determine if the problem pertains to before you begin repairs or at least have an idea of what is wrong when you take your vehicle into the repair garage. For more information on how to retrieve trouble codes from your vehicle. Learn more

Once you have determined the trouble code is in fact a problem code P0454 the inspection can begin.

A vacuum line that is connected to the engine intake manifold, this is used to supply vacuum to the system which helps gather the gas fumes so they can be condensed inside the charcoal canister. A vacuum pressure sensor is located at the fuel tank which monitors this vacuum supply and its ability to hold vacuum for a period of time. If no vacuum is detected or the system leaks it will cause an EVAP code and the check engine light to come on.

Step 1

Start your inspection at this feed line by checking for tears or cracks in the line that feeds the vacuum control solenoid and is mounted either on the intake manifold or near the fender well of the vehicle. On vehicles that have a plastic vacuum line check the O ring seals, when these seals age they become loose as they flatten and allow leakage around the seal.

Step 2

To check these O rings there is a release tab the must be activated to allow the tubing to be removed, every automobile manufacture is a little different, but follow the same principle. Use a small standard screw driver or pick to push the release clip downward while gently pulling the tube from the connector.

Step 3

The vacuum control solenoid is controlled by the computer which acts as a simple valve that opens the vacuum port and then closes it. This solenoid is a basic 12 volt power and ground unit which is prone to failure and is easy to replace. One side of the valve is connected to the intake manifold while the other is routed back to the charcoal canister.

Step 4

Use a floor jack and jack stands to lift the vehicle safely to inspect the charcoal canister under the rear part of the vehicle near the fuel tank, although is some older vehicles this can be located under the hood. Check all of the hoses to make sure they are connected and in good shape, replace any of the hoses found to be leaking.

On the canister is where you will find the purge solenoid which is also prone to failure, but will have a specific code for the failure, not a leak code unless the seal to the canister for the purge valve is leaking.

Step 5

After checking the system I found the O ring seals to be worn due to wear and age in the tubing that connected the intake manifold vacuum to the vacuum control solenoid. I did this by moving the tube and seeing that it was loose and no way could hold a seal especially when the engine was running and under vibration.

I released the tube from the intake and vacuum control valve for further inspection to find the worn O ring seals.

Step 6

I then ordered a new EVAP tube for it and when it arrived I matched it to the old unit to make sure it was going to work. This kind of part is only available from the dealer and if they have the part "in stock" you can bet this is the problem because dealerships mostly carry what commonly goes wrong with their vehicles so there mechanics can get the repairs completed quickly.

Step 7

Before installing the new tube and O rings use a small amount of lubrication to allow the O rings to slip into place without tearing this will ensure a better seal.

Step 8

Use a shop towel and clean both ends where the tube connects. Also, the intake manifold port and the control solenoid so the new O rings have a clean surface to seal to without damaging the O ring itself. Dirt and grime can cause the new seals to leak which would void the repair and will need to be done all over again so taking your time doing the job right is definitely worth its while

Step 9

With both connections clean and free from dirt gently press the tube back into place onto the vacuum control solenoid; it will let you know when it is fully installed by a slight click as the clip locks into place.

Step 10

Next, press the opposite end of the tube down onto the intake port until you hear the same small click to indicate the tube is fully installed. Once the job is completed be sure to clear the trouble codes and allow several cycles of the vehicle running. Then parked overnight and then ran again to ensure the problem is fixed. The system runs through many cycles before the computer monitor for the system can set, and deemed to be okay.

Also See: Fixing a P0454 Code Video

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Article first published