Q: I have a 2009 Dodge Durango with a 4.7-liter V-8. The vehicle has the trouble code P0455. So far, I've replaced the evap purge solenoid and the gas cap. Please help!
A: Evaporative emissions system diagnosis is never an easy thing. It's a complex series of components and hoses designed to capture hydrocarbons in gas tank fuel vapors, preventing them from entering the Earth's atmosphere. It accomplishes this by storing the hydrocarbons in a charcoal canister that is eventually purged by engine vacuum and burned up in the combustion chamber. DTC P0455 is caused by a relatively large vapor leak in the purge part of the evap system. This involves the vacuum path from the engine's intake manifold to the evap canister. The purge valve was a good guess, but a leak at the gas cap technically would set a different DTC. From experience, evaporative emissions DTCs can be tricky. Diagnosis instructs inspecting for leaks in one section, while the true cause is actually in another. Plus it may not be an external leak of vapor. It could also be an internal component leak, or electronic failure. Make a few more checks, and get it to Dodge service if you don't come up with anything. It will be worth the money.
The best way to check for external evap leaks is with a smoke tester. You would apply the smoke at the purge valve, crimp the purge hose at the canister, and see where the smoke comes out. It could be a damaged hose or poor connection. Without a smoke machine, you can use a handheld vacuum pump in the same manner to see if it holds vacuum. If it doesn't, there's a leak between the purge valve and canister, but you still have to pinpoint the spot. Another component to keep in mind is the evaporative system integrity monitor switch. This is located in line between the purge valve and the evap canister. Without getting into details, its function is to help the PCM test the system for leaks. A failure of this component can also set DTC P0455. Again, don't get too deep on this one.
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