P0456 OBD-II: Evaporative Emission System Leak Detected (very small leak)

What does code P0456 mean?

Code P0456 indicates a small leak detected in the Evaporative Emissions (EVAP) system.

The evaporative emissions (EVAP) system is designed to prevent fuel vapors from escaping into the atmosphere. To accomplish this, the vapors are captured and stored. Then, when the time is right, the vapors are pulled into the engine and burned.

A typical EVAP system is a complex system. These are the main components:

• The charcoal canister. As the name implies, the charcoal canister contains charcoal which absorbs and stores the fuel vapors. When the time comes to “purge” the vapors, fresh air passes over the charcoal. This releases the vapors.
• Purge solenoid and valve. When engine operating conditions are correct, the purge solenoid opens the purge valve. This allows fuel vapors to be sucked into the engine and burned.
• Canister vent solenoid and valve. Enhanced EVAP systems use a canister vent solenoid and valve during system self-testing. The PCM closes the valve, sealing the canister off from outside air. Then, the PCM can monitor the closed system and check it for leaks.

Once the engine is shut down, the powertrain control module (PCM) tests the integrity of the EVAP system. It does this by closing off the system and monitoring pressure/vacuum to check for leaks. Code P0456 indicates the PCM has detected a small leak in the EVAP system during testing.

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P0456 Symptoms

• An illuminated check engine light

Common causes for P0456

Code P0456 is typically caused by one of the following:

• A leaking EVAP hose
• A problem with the purge valve or vent valve
• A loose or faulty gas cap

How to diagnose and repair P0456

Begin by checking the gas cap to make sure it’s tight. Even if the cap seems secure, it may not be sealing well. Gas caps are inexpensive, so if you have any doubt, replace the cap and clear the code.

Next, perform a visual inspection of the EVAP system, looking for broken hoses or visibly damaged components. If a problem is found, repair it and clear the code. If nothing is found, check for technical service bulletins (TSBs) regarding the issue. If these preliminary measures don’t yield any results, you’ll need to move forward with a step by step system diagnosis.

The following is a general diagnostic procedure. Refer to the manufacturer’s repair information for vehicle-specific diagnostic information.

It’s a good idea to consult the factory repair information and wiring diagrams before proceeding.

Check for leaks

Without the proper equipment, finding a small EVAP leak can be nearly impossible. An OEM-level scan tool and smoke machine are suggested. The good news is, you can make your own smoke machine from an old paint can. You can also buy these homemade smoke machines fully assembled on eBay. They use mineral oil commonly found at the drug store.

If an OEM-level scan tool is handy, you can use it to run an EVAP system self-test. This convenient feature seals the EVAP system and checks for leaks. The test results will indicate if a leak is present, eliminating any second guesses.

To use the smoke machine, you must first make sure the EVAP system is sealed. This means both the purge valve and vent valves must be closed. An OEM-level scan tool can be used to close the valves. If one is not available, the valves can be manually closed by jumping them to power and ground.

Note: some systems use solenoids that are normally closed, while others use solenoids that are normally open. It’s a good idea to determine which type your vehicle has before attempting to close the system.

Once the system is sealed, a smoke machine can be used to locate the leak. Connect the smoke machine to the vehicle’s EVAP test port (found in the engine compartment under a green cap). Turn the machine on and look for smoke billowing out, indicating the source of the leak.

Test the purge valve and vent valve

Typically, a problem with the purge or vent valve will result in additional code being set, not just P0456. However, if no leaks were found, it’s a good idea to test the valves.

Start by attaching a hand-held vacuum pump to the vent valve. Close the vent valve by jumping to power and ground with a pair of jumper wires. Apply vacuum to the valve with the hand-held pump and watch the gauge. If the valve is sealing properly, the gauge should hold steady. If not, it’s faulty. Repeat this test for the purge valve.

Note: some systems use solenoids that are normally closed, while others use solenoids that are normally open. It’s a good idea to determine which your vehicle has before attempting to close the valves.

Other diagnostic codes related to P0456

• P0455: Code P0455 indicates the PCM has detected a large EVAP system leak.
• P0457: Code P0457 indicates the PCM has detected an EVAP system leak.

Code P0456 technical details

The EVAP monitor is non-continuous. This means the system is only tested and monitored under certain conditions. For code P0456 to be set, the ignition must be off, the fuel must be at a certain level and ambient temperature must be within a pre-defined range.