Customer Concern: Malfunction Indicator Light (MIL) is on. Trouble code P0455. Evaporative Emission Control System (EVAP) major leak code. Has checked the gas cap and it is good.
Tests/Procedures: 1. At the purge valve, remove the hose going underneath the vehicle. With a smoke machine apply smoke to that line.
2. There will be a leak through the vent valve. To eliminate this, either apply power and ground to the vent valve, or just block off the hose at the tank filler neck (after the vent filter).
3. Check for any leaks.
4. If no leaks are found, check the purge valve for leaking by running the engine at idle, disconnecting the connector and feeling for any vacuum leakage through that valve. Apply power and ground that valve and keep checking for vacuum loss when there is no power and ground at the valve to check for an intermittent failure.
Tech Tips: It may be a good idea to clear the code and see if it comes back before getting too deep into troubleshooting, or run a fuel system quick test with a scan tool to see if it is a permanent or intermittent problem.
Some leaks have been found where the hard plastic hose goes around the sub frame or where it goes between the sub frame and steering rack.
Intermittent failures of the purge valve also have been found.
Unless you have a smoke machine it will be diificult to fix. Take it to a qualified repair shop.