Postby smj999smj » Mon Feb 23, 2015 12:22 pm
As you can see from your own link, there are several different possibilities that can cause the P0456 evap small leak code. Often, the first thing checked or replaced is the gas cap, but unless it is improperly installed, it's often not the problem. As far as the TSB, it doesn't apply to the 2008 model in as far as the filter kit, because you probably have it installed from the factory. The other part of the TSB, which is the canister vent control valve, is a very good possibility. The vent control valves, which have been updated several times over the years, have been a common source of problems since they were introduced in 1995. Their function is simple; they are normally open allowing the evaporative emissions system to vent through the charcoal canister, which stores fuel vapors until they can be later sent to the engine to be burned in the combustion process. The evaporative emissions system has a self-test process to check for leaks in the system. When this occurs, the vent control valve is closed and vacuum is applied from the intake manifold and this is monitored by the evap pressure sensor. The vent control valves have had a history of sticking, either closed or open. You can component test it by removing it from the canister and blowing through it. Remember, it is normally open. Apply 12v and ground to the appropriate terminals and the valve should close, and you should not be able to blow through it.
The vent control valve being the most common cause, any leak in the system or a bad purge valve can cause the code, so the only way to be 100% sure is to test the system per the factory service manual, which includes using a scantool to operate the vent valve and the ability to monitor the pressure sensor as well as an evap test port adapter and vacuum pump. A smoke machine is an even better way to test for leaks, but it is an expensive piece of equipment.