Hi, I have a scanner cause engine light is on, shows vacuum leak large. tried new gas cap, cleaned filler tube where gas cap contacts, replaced a plastic tube from valve cover to air filter hose. tried to locate by using a propane torch gas with no difference in running, not sure how to check plastic tube to tank. got a vacuum gauge to check manifold. not sure where to put gauge to troubleshoot. any ideas? also service manuals seem non existent. thanks, Steve

DTC P0455: Evaporative Emission (EVAP) System Large Leak

Circuit/System Description
The powertrain control module (PCM) tests the evaporative emission (EVAP) system for a large leak. The PCM monitors the fuel tank pressure (FTP) sensor signal to determine the EVAP system vacuum level. When the conditions for running are met, the PCM commands the EVAP canister purge solenoid valve OPEN and the EVAP vent solenoid valve CLOSED . This allows engine vacuum to enter the EVAP system. At a calibrated time, or vacuum level, the PCM commands the EVAP canister purge solenoid valve closed, sealing the system, and monitors the FTP sensor input in order to determine the EVAP system vacuum level. The following table illustrates the relationship between the ON and OFF states, and the OPEN or CLOSED states of the EVAP canister purge and vent solenoid valves.

The red X by the 02 sensor on your scan tool has nothing to do with.


You had the gas cap and the purge valve replaced, how about the vent valve under the back of the car. These go bad, cause large leaks. Also check the fuel fill tube,they like to rust out causing large leaks. If all that is good you may won't to it to a repair shop an have it smoke tested.

Possible causes
- Missing or loose fuel cap
- Incorrect fuel filler cap used
- Fuel filler cap remains open or fails to close
- Foreign matter caught in fuel filler cap
- EVAP canister or fuel tank leaks
- EVAP system hose leaking
- Fuel tank leaking
What does this mean? Tech notes
The P0455 it's a very common code, because the code is set if the gas cap is loose or missing. Start by tighten the gas cap and clearing the code. In most cases the code can be clear by disconnecting the car battery for about 30 minutes.
What does this mean? When is the code detected?
Evaporative Emission System (EVAP) control system has a very large leak such as fuel filler cap fell off, EVAP control system does not operate properly.
Possible symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
- Possible a noticeable fuel odor caused by the release of fuel vapors
P0455 Mitsubishi Description
This diagnosis detects leaks in the Evaporative Emission System (EVAP) purge line using engine intake manifold vacuum. If pressure does not increase, the Engine Control Module (ECM) will check for leaks in the line between the fuel tank and EVAP canister purge volume control solenoid valve under the following vacuum test condition.
The vacuum cut valve bypass valve is opened to clear the line between the fuel tank and the EVAP canister purge volume control solenoid valve. The EVAP canister vent control valve will then be closed to shut the EVAP purge line off. The EVAP canister purge volume control solenoid valve is opened to depressurize the EVAP purge line using intake manifold vacuum. After this depressurization is implemented, the EVAP canister purge volume control solenoid valve will be closed.

Read more: http://engine-codes.com/p0455_mitsubishi.html#ixzz3NlVyARyX

could be your oxygen sensor or catalytic converter.. You may check for leaks in manifold as well.Mass air sensor could also be at fault.

Possible causes - Missing or loose fuel cap
- Incorrect fuel filler cap used
- Fuel filler cap remains open or fails to close
- Foreign matter caught in fuel filler cap
- EVAP canister or fuel tank leaks
- EVAP system hose leaking
- Fuel tank leaking The P0455 it's a very common code, because the code is set if the gas cap is loose or missing. Start by tighten the gas cap and clearing the code. In most cases the code can be clear by disconnecting the car battery for about 30 minutes.

When is the code detected? EVAP control system has a very large leak such as fuel filler cap fell off, EVAP control system does not operate properly. Possible symptoms - Engine Light ON (or Service Engine Soon Warning Light)
- Possible a noticeable fuel odor caused by the release of fuel vapors P0455 Buick Description This diagnosis detects leaks in the Evaporative Emission System (EVAP) purge line using engine intake manifold vacuum. If pressure does not increase, the Engine Control Module (ECM) will check for leaks in the line between the fuel tank and EVAP canister purge volume control solenoid valve under the following vacuum test condition. The vacuum cut valve bypass valve is opened to clear the line between the fuel tank and the EVAP canister purge volume control solenoid valve. The EVAP canister vent control valve will then be closed to shut the EVAP purge line off. The EVAP canister purge volume control solenoid valve is opened to depressurize the EVAP purge line using intake manifold vacuum. After this depressurization is implemented, the EVAP canister purge volume control solenoid valve will be closed.
if tightening the cap or replacing the cap does not help take your car to a shop to have it diagnosed as it requires special tools/equipment to test this and get an accurate results to find what needs replacing.

Check the purge solenoid under the hood common problem in mazda 5 6 cx7.

The code is for a large leak in the EVAP system such as a loose or missing gas cap. But it could also mean a loose or missing hose to the canister or other leak in the tank.
The computer vents the tank several times an hour while the engine is running, and it checks the system by pressurizing the gas tank. If the tank will not hold pressure the code is set.
You may have to check the top of the tank where the fuel pump gasket is, as well as the vent lines to the front of the car.
A mechanic would perform a smoke test to look for leaks.

THE FUEL FILLER TUBE SEAL WHERE GAS CAP LEAKING OR THE THE TOP LARGE O - RING SEAL ON TOP OF FUEL TANK TO THE FUEL FILTER HAS A EVAP LEAK.

P0456 = "Evaporative emission (EVAP) control system leak detected (very small leak)."

It's a leak in your evap system. Causes: *Loose or missing fuel cap. *Evap canister broke, hose cracked or not connected. *Purge or vent solenoid defective *Vacuum leak at engine good luck

that can be something as simple as a bad or loose gas cap ... the cap must seal in order to develop a slight vacuum in the tank thats is used by the emmission control system. less likely but possible is damage to the several hoses that go from the tank to the evaporation control system in the engine compartment..
check your gas cap for damaged or missing rubber seal .. or just replace it ... clean the filler tube if needed so that the gas cap will seal properly .. check the flex hose (if any) from the filler nozzle to the tank ...