System Description
The Evaporative Emission (EVAP) System is used to store fuel vapors to reduce the amount of unburned fuel from escaping into the atmosphere. The EVAP system consists of the EVAP canister, the fuel tank pressure (FTP) sensor, the EVAP lines and hoses, the EVAP canister purge solenoid valve which is normally closed, the EVAP service port, the EVAP canister vent solenoid valve which is normally open, the fuel tank, and the engine control module (ECM). The ECM monitors the EVAP system for circuit faults in the FTP sensor, the EVAP canister purge solenoid valve and the EVAP canister vent solenoid valve circuits. The ECM also monitors the EVAP system for small and large leaks. During the DTC P0455 diagnostic, the ECM monitors the FTP sensor for an atmospheric pressure reading when all of the DTC parameters have been met with the engine running. The ECM will then command the EVAP vent solenoid ON, closed valve, and command the EVAP canister purge solenoid valve to a fixed duty cycle. The ECM will let the pressure drop in the fuel tank for a certain length of time, after which it will turn OFF the EVAP canister purge solenoid valve. If a correct amount of vacuum is achieved, the ECM will run the DTC P0442 diagnostic, which will monitor the decay in the vacuum of the sealed system over a calibrated amount of time. DTC P0442 sets when the vacuum decay is more than the calibrated amount for a certain length of time due to a small leak.

Diagnostic Aids
• An EVAP canister purge solenoid valve or EVAP canister vent solenoid valve circuit fault may have caused this DTC to set.

• The ECM uses the FTP sensor to detect the amount of vacuum pulled on the EVAP system during the leak diagnostic tests. Ensure that the fuel pressure sensor is not skewed by verifying the FTP sensor on the scan tool is between 1.30-1.70 volts with the ignition ON and the fuel cap removed.

• Locate the small leak with the J 41413-200 (J 41413-100) Evaporative Emission System Tester.

• The following are possible causes of a small leak:

- The fuel cap is leaking.

- The EVAP canister vent solenoid valve is not seating correctly.

- The EVAP vent hose is loose or damaged.

- The EVAP canister is leaking.

- The fuel sender assembly O-ring is leaking.

- The fuel tank or filler neck is leaking.

• The small leak diagnostic can detect a leak greater than 0.020 of an inch in diameter.

• A condition may exist where a leak in the EVAP system only exists under a vacuum condition. By using the scan tool Purge/Seal function to create a vacuum, seal the system and observe the FTP parameter for vacuum decay, this type of leak may be detected. System Description The Evaporative Emission (EVAP) System is used to store fuel vapors to reduce the amount of unburned fuel from escaping into the atmosphere. The EVAP system consists of the EVAP canister, the fuel tank pressure (FTP) sensor, the EVAP lines and hoses, the EVAP canister purge solenoid valve which is normally closed, the EVAP service port, the EVAP canister vent solenoid valve which is normally open, the fuel tank, and the engine control module (ECM). The ECM monitors the EVAP system for circuit faults in the FTP sensor, the EVAP canister purge solenoid valve and the EVAP canister vent solenoid valve circuits. The ECM also monitors the EVAP system for small and large leaks. During the DTC P0455 diagnostic, the ECM monitors the FTP sensor for an atmospheric pressure reading when all of the DTC parameters have been met with the engine running. The ECM will then command the EVAP vent solenoid ON, closed valve, and command the EVAP canister purge solenoid valve to a fixed duty cycle. The ECM will let the pressure drop in the fuel tank for a certain length of time, after which it will turn OFF the EVAP canister purge solenoid valve. If a correct amount of vacuum is achieved, the ECM will run the DTC P0442 diagnostic, which will monitor the decay in the vacuum of the sealed system over a calibrated amount of time. DTC P0442 sets when the vacuum decay is more than the calibrated amount for a certain length of time due to a small leak. Diagnostic Aids • An EVAP canister purge solenoid valve or EVAP canister vent solenoid valve circuit fault may have caused this DTC to set. • The ECM uses the FTP sensor to detect the amount of vacuum pulled on the EVAP system during the leak diagnostic tests. Ensure that the fuel pressure sensor is not skewed by verifying the FTP sensor on the scan tool is between 1.30-1.70 volts with the ignition ON and the fuel cap removed. • Locate the small leak with the J 41413-200 (J 41413-100) Evaporative Emission System Tester. • The following are possible causes of a small leak: - The fuel cap is leaking. - The EVAP canister vent solenoid valve is not seating correctly. - The EVAP vent hose is loose or damaged. - The EVAP canister is leaking. - The fuel sender assembly O-ring is leaking. - The fuel tank or filler neck is leaking. • The small leak diagnostic can detect a leak greater than 0.020 of an inch in diameter. • A condition may exist where a leak in the EVAP system only exists under a vacuum condition. By using the scan tool Purge/Seal function to create a vacuum, seal the system and observe the FTP parameter for vacuum decay, this type of leak may be detected.

Hooking up a smoke machine to check for leaks is normally have a repair shop checks to see what's leaking .https://www.youtube.com/watch?v=LNaJTP-6... Hooking up a smoke machine to check for leaks is normally have a repair shop checks to see what's leaking . https://www.youtube.com/watch?v=LNaJTP-6u1s&t=444s