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Old 07-18-2019, 03:59 AM
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smj999smj smj999smj is offline
Master Enthusiast
2006 Pathfinder
2003 Frontier King Cab
2003 Frontier KC SVE 4x4
Join Date: Jun 2012
Location: Prospect, VA
Posts: 1,849

It sounds like you are talking about the front diff vent hose, which mounts to a bracket on the back side of the air cleaner box. If that's the hose you are talking about, then it's not supposed to be connected to anything. Pictures help in this case, but it's a common question regarding the vent hose.

P0455 is a large leak code for the evaporative emission system, which is the charcoal canister (and it's related hoses, sensors, valves, etc.) that stores the fuel vapors from the gas tank until they can later be sent to the intake manifold and burned in the engine. The canister is behind a plastic cover at the back of the driver's rear wheel well, where lots of mud and dust get kicked all over it. The proper way to diagnose this system is with a smoke machine and a scan tool to command the vent control valve to close and monitor the evap pressure sensor. Many times the cause is the vent control valve, itself, located at the top of the canister. Normally, it is "open" and you can breathe through it to test it. When 12v and ground are applied to it, the valve should close and you should not be able to breath through it. Since the code is "large leak," the valve not closing would be the concern. Of course, there are other parts of the system that can cause a leak code, like the "O" ring at the top of the fuel pump module or a disconnected hose in the system...or even a faulty pressure sensor or loose or faulty gas cap. The only way to be sure it to do the P0455 diagnostics per the FSM. If you want to try component testing the vent control valve, itself, be prepared to get dirty! There's a 12MM head bolt you get from under the vehicle that keeps the vapor canister mounted---and it will likely be rusty and a bunch of dirt will fall all over your arm as you remove it. You'll need to take the driver's rear wheel off and the plastic panel on the wheel well (you'll probably break a few plastic push-clips in the process). You can then see a few hoses and lines with "quick-disconnect" fittings on them that are never "quick" or seem to want to "disconnect" because they are jammed up with dirt and dust or want to break because they are brittle. The vent control valve will be towards the back, where there's never enough room for my fat hands! Once the get the electrical connector and hose off of the valve, it turns counter-clockwise and then pulls straight out, or, at least that's the way it's supposed to work. The rubber seal on it usually holds pretty well and pulling the valve out without breaking anything can be an issue. Once you get it out, then you can apply power and ground to the appropriate terminals and to the "blow" test" to see if it closes. Good luck!
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