P0456 code definition
A small leak from the exhaust gas evaporation system has been detected
What does the code P0456 mean?
P0456 is a generic OBD-II code that indicates that the engine control module (ECM) has detected a very small leak in the evaporative system during a vehicle stall test. The test must fail twice in a row for the ECM to trigger the code.
What causes the P0456 code to occur?
The ECM tells the purge control valve to close the system and activates the evaporative vacuum pump to bring the system to a certain small vacuum value, and then monitors the system for leaks. If the system detects a very small leak during the test, then the ECM records the code and waits until a second test can be performed, and if this test detects a very small leak, then the ECM records the code P0456 and activates the check engine light.
The cause of the P0456 code may be a small leak in any of the system components or hose connections.
The two most common causes of this code are a fuel cap vent and a vent valve that is not fully tightened.
What are the symptoms of the P0456 code?
The Check Engine light will come on, and the code will be stored in the ECM 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.
- Check the entire steam purge valve system, including the purge valve and air purge valve hose connections for damaged or loose connections.
- Inspect the purge valve vent for debris, debris, or cobwebs that may cause the valve to be unable to completely seal off steam.
- Perform a smoke test on the fuel vapor system to try to locate the cause of the vapor leak using the test vapor port, check the fuel cap for leaks from the vent line.
- Check the purge control valve to see if it maintains vacuum when turned on.
Most common errors in the diagnosis of P0456 code
- Not checking and assuming that the purge control valve is defective without performing a complete diagnosis of the entire system and then determining that the lines are damaged or cut
- Failing to check for leaks and replace parts that may or may not be causing the problem
- Failure to check service bulletins that may contain a solution to the code
How serious is code P0456?
- The P0456 code causes the check engine light to come on and this fact alone causes a failed emissions test.
- This code indicates that there is a very small leak in the fuel vapor system and may be difficult to locate on some vehicles, and the code will continue to appear until the leak is found.
- The ECM monitors will not pass emissions if the leak is not found and only the Check Engine light goes out.
What fixes can repair a P0456 code?
- Replace the leaking fuel cap.
- Replace leaking or clogged air bleed valve.
- Replacing a leaking air bleed valve
Additional notes on 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 light with this code, the most common cause is that the fuel cap or the purge or control vent valve does not completely retain vapor and has very small leaks that are detected.
