Error P0456 – how to fix?

Code definition P0456

A slight leakage from the exhaust gas evaporation system has been detected

What does the code P0456 mean?

P0456 is a generic OBD-II code indicating that the engine control module (ECM) detected a very small leak in the evaporation system during the vehicle shutdown test. The test must fail two times in a row for the ECM to trigger the code.

What causes the code P0456?

The ECM commands the purge control valve to close the system and activates the evaporation vacuum pump to bring the system to a specified, small vacuum, then monitors the system for leaks. If the system detects a very small leak during the test, then the ECM saves the code and waits for a second test that can be run, and if this test detects a very small leak, then the ECM writes P0456 and turns on the check engine light.

The cause of the P0456 code may be a slight leak in any of the system components or the hose connections.

The two most common reasons for this code are the fuel cap breather and the breather valve is not completely tight.

What are the symptoms of the P0456 code?

The Check Engine light will come on and the code will be stored in the ECM’s memory.

How can a mechanic diagnose the P0456 code?

• Scan the codes and document the code in the ECM, review the freeze frame data to see when the fault occurred.
• Inspect the entire bleed-type steam valve system, including the bleed-off valve and bleed valve hose connections for damaged or loose connections.
• Checks the purge valve vent for debris, debris, or cobwebs that may prevent the valve from completely sealing the vapors.
• Perform a smoke test on the fuel vapor system to try to locate the cause of the vapor leak with the test vapor port, check the fuel cap for vent leak.
• Checks the purge control valve to see if it maintains a vacuum when turned on.

The most common errors when diagnosing the P0456 code

• Failure to check and assume that the purge control valve is faulty without thoroughly diagnosing the entire system and then finding that the lines are damaged or cut
• Failure to check for leaks and replace parts that may or may not be the cause of the problem
• Failure to check service bulletins that might contain a solution to the code

How serious is the P0456 code?

• The P0456 code turns on the check engine light and this alone causes the exhaust emission test to fail.
• This code means that there is very little leak in the fuel vapor system and may be difficult to locate in some vehicles, and the code will continue to run until the leak is found.
• The ECM monitors will not pass the emissions if no leak is found and only the Check Engine light goes out.

What repairs can fix the P0456 code?

• Replace leaking fuel cap.
• Replace a leaking or clogged bleed-type air valve.
• Replace a leaking vent valve

Additional notes regarding code P0456

The P0456 code is not a common code for most vehicles, and some manufacturers do not use this code at all. Vehicles that come with an engine check lamp with this code, the most common cause is that the fuel cap or check bleed valve or breather valve is not holding the vapors completely and has very small leaks that are detected.