P0449 - Evaporative Emission Control System Vent Valve/Solenoid Circuit Malfunction
Diagnostic fault codes never say to replace parts or that they're defective. They only indicate the circuit or system that needs further diagnosis. The problem with having the guys at auto parts stores read codes for you is they understand selling parts, not diagnosing the cause of the problem. In this case corroded or stretched terminals in an electrical connector, or a cut wire will be the cause about half of the time.
Your mechanic has an entire book on how to troubleshoot each fault code. He will start by connecting a scanner to command the circuit to operate, then he will take voltage measurements to see if the vent valve should be activating. Without a scanner, about all you can do is a visual inspection of the wiring. Usually the vent valve will not open at idle or low vehicle speeds to prevent running problems. Without a scanner you would have to take voltage readings while running alongside the vehicle. Obviously, that is not practical.
There are different codes that can be set related to the flow of the stored fuel vapors. When the valve is opened, those vapors drawn into the engine result in the exhaust gas going rich. The Engine Computer expects to see that. When no change takes place between rich and lean conditions when the valve is opened, the computer knows there's a problem with flow. Code 449 refers to an electrical problem. When that code is set, the computer knows there won't be any change in flow so it won't set a code for that.
The location of various valves differs depending on model and engine size. There's a sticker under the hood that shows vacuum hose routing. That will show the valves related to the charcoal canister.
Sunday, October 13th, 2013 AT 12:20 PM