Need a P0456 diagnosis? Trust our experts.
Oops! We got lost!
Your location cannot be detected. Please enter your zipcode for nearby shops.
P0456 Severity
Once the vehicle's onboard system no longer detects the issue, most codes will disappear on their own. If your vehicle still has this code, however, it should be properly diagnosed to avoid a more serious problem.
For a proper diagnosis, RepairPal Certified shops have the equipment, tools, and expertise.
Moderate severity codes might not threaten the vehicle's safety or functionality immediately, but you should still get it diagnosed within a reasonable time frame to keep your car running well.
The evaporative control (EVAP) system captures any fuel vapors from the fuel tank and sends them through the vehicle's intake to be burned in the normal combustion process. When the engine control module detects a leak in this system, it will set code P0456.
RepairPal Car Genius™ is a free resource for vehicle owners seeking advice on maintenance, auto repair, shop inquiries, estimates, and finding a trustworthy repair shop in your area.
Call us at 877-913-1554
Available 9am – 6pm ET Monday through Friday
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:
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.
Get this problem diagnosed by a professional. Find a shop in your area
Code P0456 is typically caused by one of the following:
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.
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.
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.
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.