2004 Chevy Cavalier...large evap leak. P0455 i believe. Gas cap has been changed. Purge solenoid is solid closed when car is off and open when car is on. and a smoke test has been done to discover the vent valve leak. Which the vent valve was changed...but the light came back on after a couple days. Still reads as a large leak. Did a 2nd smoke test...no smoke outta anywhere. My mechanic and I are starting to get stumped as to why this wont shut down and stay off. Do I need a new fuel intake line or what??

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.

The check engine light went off on it's own ? Before replacing the purge solenoid did you test the evap system by smoke checking ? Would have other code's besides P0455 if purge solenoid was bad. DTC P0455: Evaporative Emission (EVAP) System Large Leak Detected
• Inspect for a loose, missing, damaged, or incorrect fuel fill cap.
• Inspect for a damaged fuel filler neck seal surface.
• A blockage or restriction in the EVAP purge solenoid valve, purge pipe, EVAP canister, or vapor pipe, can cause this DTC to set.
• The EVAP system can be filled with smoke more quickly and completely by opening the system opposite the end where the smoke is injected. For example, when injecting smoke at the service port remove the fuel fill cap, or temporarily leave the vent open, until smoke is observed, then close the system and continue testing. If using a fuel cap adapter at the filler neck, use the J 41413-VLV at the service port to allow the system to fill faster.
• To help locate intermittent leaks using the J 41413-200 , move all EVAP components while observing smoke with the J 41413-SPT .
• Individual components can be isolated and tested using adapters in the J 41413-300 .
• A condition may exist where a leak in the EVAP system only exists under a vacuum condition. This type of leak may be detected by using the scan tool Purge/Seal function to create a vacuum in the EVAP system and then observe the FTP parameter for vacuum decay.

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

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.

Here is the definition and possible causes.

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
P0455 CHEVROLET 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_chevrolet.html#ixzz24fVfq0Bx

P0449 - Evaporative Emission Control System Vent Valve/Solenoid Circuit Malfunction

P0455 - Evaporative Emission Control System Leak Detected (no purge flow or large leak)

Both are refer at EVAP system; other EVAP DTCs: P0440 - P0441 - P0442 - P0443 - P0446 - P0453 - P0455 - P0456

This indicates a fuel vapor leak or lack of purge flow in the EVAP control system. It means a large leak has been detected. The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.

Symptoms: You likely won't notice any drivability problems.
Causes: most likely means one or more of the following has happened:
A loose or improperly affixed gas cap
A non-conforming gas cap (i.e. not factory/original brand)
Other leak or damaged piece in EVAP system

Possible Solutions: the most common repair is to:
Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.
Otherwise, replace the gas cap, and/or
Inspect the EVAP system for cuts/holes in tubes/hoses (you may hear a vacuum noise or smell fuel), repair if necessary


Hope helps.

DTC P0455 - Evaporative Emission Control System Leak Detected (no purge flow or large leak)

This indicates a fuel vapor leak or lack of purge flow in the EVAP control system. It means a large leak has been detected. The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.

Symptoms: You likely won't notice any drivability problems.

Causes: A code p0455 most likely means one or more of the following has happened:
* A loose or improperly affixed gas cap
* A non-conforming gas cap (i.e. not factory/original brand)
* Other leak or damaged piece in EVAP system

Possible Solutions: With a p0455, the most common repair is to:
* Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.
* Otherwise, replace the gas cap, and/or
* Inspect the EVAP system for cuts/holes in tubes/hoses (you may hear a vacuum noise or smell fuel), repair if necessary

Test it and send us news.

Trouble code P0455-EVAP Control System Large Leak Detected

Trouble Code Conditions:
ECT sensor less than 90°F at startup, engine running, and the PCM detected several small fuel vapor leaks or a large leak in the system.

Possible Causes:

• Aftermarket EVAP hardware non-conforming to specifications
  
• Canister vent (CV) solenoid stuck open
  
• EVAP canister purge valve stuck closed, or canister damaged
  
• EVAP canister tube, EVAP canister purge outlet tube or EVAP return tube disconnected or cracked, or canister is damaged
  
• Fuel filler cap missing, loose (not tightened) or the wrong part
  
• Loose fuel vapor hose/tube connections to EVAP components
  
• Purge sensor or FTP sensor is out of calibration or has failed
  

CODE PO455 - EVAP SYSTEM LARGE LEAK DETECTED CONDITIONS.POSSIBLE CAUSES FUEL CAP LOOSE MISSING,FUEL TANK FULLER NECK OR FUEL SENDING UNIT O - RING IS LEAKING, FUEL TANK PRESSURE SENSOR IS DAMAGED,FUEL TANK VAPOR LINES,CLOGGED,DAMAGED,OR DISCONNECTED,PURGE VALVE VAPOR LINE IS CLOGGED,DAMAGED,OR DISCONNECTED,PURGE SOLENOID IS NOT OPENING,IT MAY BE DAMAGED OR STICKING,VENT SOLENOID IS NOT CLOSING,MAY BE DAMAGED OR STICKING,PCM HAS FAILED.

your problem is probably a vacuum hose that goes from the purge valve to the gas tank (crack or broken hose). There should be two of these check both. A broken vacuum line will make the purge valve make a clicking noise that can be mistaken for noisy engine valves.