Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Got a p0455 code (EVAP Gross Leak)?

I got 04 Nissan Sentra and a p0455 code popped up couple days ago. I did try to remove the valve cover for some other issue but was stuck on, but did develop some minor leaks because the valve cover is now a little dirty on top. The 2 hoses that are connected to the valve cover were removed and took out the Variable Valve Timing Solenoid to test it. Don’t know if that has something to do with the code?

So I tested to see if the fuel cap was the problem. I put some vasoline on the fuel cap gasket, clear the code on my scan tool and within 15 miles had the code as pending then about 30 miles the CEL lite up.
Then I tryed a new fuel cap and had (somewhat) better success. I cleared the code drove it 50 miles and noticed my monitors were reset and no codes, so I thought it was fixed. At 95 miles the CEL lite up but then went out at 112 miles. I check my scan tool if the code was gone but it was still there as a DTC, not pending. And now with 285 miles the light came back on. This was in a span of 4 days.

What the next thing I should do to diagnose the code? If I search p0455 nissan on youtube, there’s alot of videos showing how to replace a Canister Vent Valve. How often is something clogged in there, should I do a smoke test and how would I do that, where would I tap into? What’s the most common causes for this code to pop up?

Why not just get a new gas cap for $10 and see if that will do it? I doubt that vasoline would be a good permanent fix.

Posted that I tryed a new fuel cap and the code eventually came back

I missed that part, sorry. Did you look at this page to get some more ideas what to look for?

Where did you get the cap from? I had an EVAP error with my 05 4runner a few years back. I went to my trusted local parts store…then I cleared the code…and about a day later the code came back.

So for the heck of it, I went to the dealer and bought an OEM gas cap. Cleared the code and never had the problem again.

It’s a stant cap but is the fuel cap a very high possibly of being the problem for a p0455 code?


Taken from the link above…

When is the code detected?

Evaporative Emission System (EVAP) control system has a very large leak such as fuel filler cap fell off, EVAP control system does not operate properly.

Yes, a bad gas cap. or one that was not properly sealed will show a P0455 ( gross Evep leak).

I just fixed one where the lady left her 25 year old grandson pump the gas and he never put the cap on at all. He just closed the fuel door. Talk about lazy. I know the kid and he lost his license a few years back. He hooks grandma into taking him everywhere, yet he never pays for the gas. I’m surprised that he even expended the energy to pump the gas for her.

As far as doing a smoke test, it pretty much a specialty job for a good mechanic.
Unless you have the smoke machine…you have to take it to a shop for testing


I would be making my own homemade smoke machine like the one’s made out of paint cans that’s seen on youtube. I would be using a pressure regulator so I don’t go over 2 psi.
Has anyone ever tryed it or know someone who has?

I’m doubting the gas cap is the problem. Giving it one more shot, cleaned the top of the filler neck with alcohol even though it wasn’t that bad, cleared the code and see what happens

I cheap cigar works most of the time…

Knowing you, you’re probably serious

There’s two seals on a gas cap. The outside rubber-o-ring you cleaned and vasolined, which forms an air-tight seal where the cap meets the filler tube entrance, and a second one that isn’t visible unless you can take the gas cap apart. The 2nd is a spring-loaded one way valve that allows air into the tank to replace the space for the fuel as it is used up. The incoming air path bypasses the first seal, otherwise it wouldn’t work. But the 2nd seal has to seal the tank from gas fumes going in the other direction too, just like the first seal. And that seal or its seat also can wear out or be defective right out of the box, which could cause an evap leak code.

Since you presumably now have one gas cap you’ve taken out of service, you could try to disassemble it and find the spring-loaded one way valve if you wanted to give it a go, so you can see what I’m talking about. I’ve done that several times myself. It has a good size but quite weak spring that can come in handy for use in other projects.

Leaks are annoying. Plumbing leaks, air leaks, all leaks. When you got one causing you grief, there’s often no simple way to tell where it is leaking; the only thing you know is you got a leak. About all you can do is eliminate the possible sources one by one. Starting with the gas cap makes sense b/c it is easy and inexpensive. If that doesn’t do it, then you’ll have to move on to the other possibilities. What those all are varies car to car. But the canister vent valve and the purge valve are both possibilities. I’m presuming the canister vent valve is designed to be open during tank re-fueling to allow air to be pushed out, but closed when the evap system is being tested by the computer for leaks. There’s often a valve on the top of the tank or near the tank too. And of course any of the hoses or hose connections can leak. If you could somehow get the computer to go into pressure test mode you might could brush soap bubbles on the suspect to find a leak, like you’d find a leak in a tire, but I’ve never heard anyone here say they do that on evap systems.

I’ve never had to worry about this problem myself b/c the evap system on my Corolla is much simpler than the way they are designed these days. The downside with the older designs like mine (for the environment) is there’s no way for the computer to periodically test whether the evap system is leaking or not. It is only tested during emissions testing. What they do is hook up a special gas cap gadget that has a connector on it that allows them to pressurize the gas tank. They must have to clamp off the canister vent path for the test. The test the cap too, with a separate gadget.

Home made smoke machine? I’d be hesitant to use that anywhere near the fuel system unless you can guarantee it is designed in a way that it won’t output anything hot, especially an ember or spark. I think the pro smoke machines use some kind of chemical reaction to make the smoke. Those only output room temperature smoke.

I would like to state a couple things that maybe could pin point the problem.

Since I last posted. The CEL has been on and off. Even on another car I had, it had a p0455 code and it went out in cold weather at times. Is that a common thing with this code?

A couple of us use this car and when filling up we overfill after the pump stops, like rounding off to the nearest dollar or on a long trip putting extra to last further. Heard this could be bad for the vapor canister and or the vapor vent valve?

About once every 3 months or so while trying to pump gas, the pump keeps on stopping like it’s full and the stopping starts a dollar into the fueling of the car. The pump stops 10 times or more. I also heard that this could be more of a vent valve problem or even vapor canister?

Can a clog somewhere pull this code because this code is defined as a (EVAP large leak) If so where most likely be the clog because smoking it out wouldn’t see anything.

Just looking to see the stuff I stated makes it more a part issue vs a leak or just narrow down the issue?

It is, don’t top off your tank

1 Like

Here is my $10 home made one:

oil paint can, some old bolts, nuts, and wires - free

$1 for 1-inch wide oil lamp wick on ebay,
$2 for a foot of resistance wire - same source
$5 for transparent vinyl tubing from homedepot
$2 for a bottle of unscented baby oil (essentially: mineral oil)

ah, 12 volts can come from either your car battery or you can get a 2A adapter as I did

the only trouble was to figure how much wire to have there so that it will not burn the wick, but will evaporate oil… I started form water and made it reliably produce water mist before drying it up and using oil

I already had regulator on compressor, so setting it low was easy to do

this thing produces a lot of smoke in 1 minute after you turn it on, smoke is not hot at all

1 Like

Oh scotty, what a guy, he has a solution with a 99 cent cigar.

Good info on your home-brew smoke machine, thanks.

If you got pump-shut-off problems filling the tank like that, for that the problem obviously isn’t a problem w/the gas cap. No gas cap used during fill-ups. When you fill the tank the gas vapors and air in the space above the nearly empty tank are displaced by the incoming fuel, and are supposed to be routed via various tubes and valves to the charcoal canister, where the gas & air is separated, the gas fumes are stored, and the cleaned air is expressed out to the atmosphere. So you got something wrong with all that. Could be a valve is stuck closed, a tube is plugged up, or the canister is plugged up. I doubt that overfilling by less than one dollar’s of gas would do it, but if you vastly overfill the tank the canister can get saturated with liquid gasoline, and that gasoline in the canister can cause the canister’s carbon to turn to dissolved grit and eventually plug up tubes and valves in the evap system.

case #1

on my 2012 Altima I had that problem right after getting it from the dealer’s lot

upon bringing it up to dealersip’ mechanics, they found that during assembly one of vapor tubes got pinched and would not allow air to recirculate, shutting down the gas pump

case #2

my “new old 2006 Pathfinder”: while doing cleanup/rustproofing, I found that fuel vapor recirculation tube is brand-spanking-new: I suspect prior owner had some EVAP leak problem, had it replaced. upon checking on Nissan forums, found it is quite common with age

considering OP’ car is 13-years-old, I can imagine much more than fuel cap could go wrong in this area…

here is some good video to he help:

So I tested the purge valve, took it out couldn’t blow threw it, put power to it heard clicking and then was able to blow threw it.
Took out the vent valve was able to blow threw, then putting power to it, heard clicking and was not able to blow threw it while powered.
I tested the connectors to see the volts coming out of it. The purge valve connector had 12v and the vent valve had 9.7v, don’t know if that’s enough volts for the vent valve?

I took off the small line (far left) of the vapor canister and the nipple that the hose plugs into was a little shiny and wet and dryed off in 5 mins, looked inside there was nothing clogged that I can see. I tryed taking off the middle bigger connection with a fuel logo on it and I could not take it off. It was a plastic hose with tabs on the side of the connection that needs to be pressed to take off. I’m going to get some hose pliers to see if that might help. What’s the best way to take off those plastic connection hoses? I did blow into the small line of the canister to see if there was anything clogged and seems like that wasn’t a problem.

What’s my next step now? Should I still take off the vapor canister and see if anything comes out of it, etc? The CEL still is on and off every 50 miles or so