Nissan Sentra P0440 P0446 MIL code EVAP leak

My 1997 Nissan Sentra is giving P0440 and P0446 MIL codes together, which means large EVAP leak. I cleared the ECM codes, but they keep coming back after a while.
The car runs fine, starts fine, no issues otherwise.
I read this can be caused by the following:
Bad gas cap, intake manifold hairline crack, bad hose, cracked charcoal canister, EVAP vent control valve solenoid not closing properly, bad EVAP canister purge valve.
I checked the usual suspects and I’m down to 3 possibilities, the charcoal canister, the EVAP vent valve/solenoid, the EVAP purge valve/solenoid.
YouTube doesn’t have any videos for replacing the canister or the vent valve for this model.
What could be causing this issue? What tests to perform to narrow down possibilities? Which item should I replace first? Is there any way to fix the parts other than buying brand new replacements?

And they will keep coming back until you fix the problem.

Some things are better left to a shop to diagnose, If you just start throwing parts at it, many times you end up spending a lot more money.

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This is one of the models that is sensitive to overfilling the gas tank. Always stop on the first click, don’t even round up to the next nickle. If this just started happening and you have been overfilling, just stopping that practice will solve the problem eventually.

If you haven’t been adding gas after the first click, then a new gas cap would be the first thing I’d try, only because it is cheaper than diagnosing the problem. But if that doesn’t work, then you could inspect all the parts, look especially for cracks in any of the rubber hoses or parts with plastic housings. If nothing is obvious, than paying for a full diagnostic would be the next best step because the parts get more expensive.

Wrong . . .

there’s actually quite a few more possibilities . . . such as a bad fuel tank sender seal, a tank that isn’t sealing, a rotten fuel filler hose, rusted out fuel filler pipe, and so on. There’s even the possibility that the root cause is electrical in nature

keith: I am not overfilling the tank. There was rust in the gas filler which I removed and I tried a new gas cap. Issue persists.
db4690: Those are directly from the official Nissan troubleshooting manual.
All: Is there a step by step troubleshooting video for Nissan (none on YouTube)? What is the proper resistance in ohms for the vent solenoid coil and the pressure sensor?

I’ve fooled around with this on GM vehicles and got lucky and found the issue. I imagine Nissan system operates similarly. In my case it was a failed open purge valve solenoid. I’d suggest checking the purge valve solenoid and vent valve solenoid before taking it to a shop. In the case of GM vehicles, you can remove those items fairly easily, apply 12 volts and ground (for GM there are only two terminals) and see if the solenoids are functional. If they are functional, you’ll hear a click and each solenoid will open or close when 12 volts are applied. GM - purge valve should open with 12 volts and close when not powered. Vent valve is the opposite. I’m fairly certain that’s correct, it’s been awhile. The main thing is, they need to change from open to closed when powered (or vice versa) and not just remain the same. You can test to see that they are opening and closing and aren’t obstructed or hanging open by blowing air through them (not compressed air, only low pressure such as with your lungs or maybe a vacuum gauge if available). Other than that, check for breaks in the hoses or loose connections. Beyond that, it’s probably time for a shop…

Thank you for sharing. I am using the Torque Pro app on my Android as the scan-tool to read the OBD information using bluetooth. I am not sure whether the Torque Pro app can send/receive commands for turning on/off EVAP monitors.
I did some testing.
When the key is on/run position (engine not started) I get 11.2 to 11.6 volt at the EVAP vent valve solenoid, so the wire harness is good.
The solenoid coil shows around 11.5 ohms resistance, but does not make any sound when energized.
I connected the solenoid to a regular 9volt battery and then a 12volt car battery but I did not hear any ticking sound of the plunger moving/closing/opening in either case. Shouldn’t there be an audible tick/click sound from the plunger when energized? Is my vent valve solenoid dead and causing this issue? Any way to repair it?

As far as I know, there’s no way to repair the solenoids if they don’t function. And yes, you should be able to hear or feel the electronic solenoid open or close. I believe if the vent valve solenoid is failed open, that could cause the “gross evap leak” code to generate. If the computer is commanding the vent valve closed, and it remains open during the evap system “self check”, that would be considered a leak.

You can try applying air to the solenoid to confirm that it’s stuck in the open (or closed position) if you want. Use a small piece of rubber hose attached to the solenoid with and without power and ground applied. If you are able to blow air through the solenoid with and without 12 volts and ground applied, it has failed open. If that is the case, I’d replace it, reset the ecm, and see if the code returned.

You can apply 12 volts and ground to the purge valve solenoid also, just to confirm that it is active and to demonstrate to yourself what an activated solenoid sounds like. In my case, the solenoids were removed from the vehicle and in my hands when I tested them, so it was easy to determine when they activated.

Hopefully the vent valve solenoid isn’t expensive, as I’d hate to send you down a money wasting path. In my case, the GM purge valve was around $30 so it was worth the gamble and I no longer have a check engine light.

One word of caution, if you do purchase a solenoid, I’d stick with an oem part. I originally purchased a Duralast part since it was in stock locally. The code returned in 2 weeks when the new solenoid failed. I exchanged it for an AC Delco part (that had to be ordered, but was actually cheaper) and haven’t had an issue since. Good luck and let us know what you find.

The exact same thing happened to a former colleague of mine

He also replaced a failed oem evap purge valve with an autozone part

Big mistake

He also bought another oem part in the end, which took care of the problem for good

But he didn’t really learn from his mistakes

He continued buying autozone parts which quickly failed on him, didn’t fit correctly, etc.

I told him that in my opinion it was easier and smarter to spend more money upfront on a high quality part and only do the job once, versus buying a cheap store brand part, have it fail, take it off, head back to the store, exchange it, replace the part again, and hope for a different result this time . . .

I verrrry seldom get parts at Autozone, but they had the part in stock with a lifetime warranty, so I took a chance. They did honor the warranty, at least. The AC Delco part was actually a little cheaper, but AZ had to order it. I just took a chance for convenience in not having to wait on the part. Turned out to not be very convenient, though…

Out of all the store brands out there . . . I’ve by FAR had the most problem with duralast parts. Could be alternators, starters, purge valves, brakes, etc.

Bottom line is this . . . if you want to increase the likelihood that you’ll get frustrated by the parts you install, by all means, buy duralast parts

I’ve had far better luck with store brand parts from O’Reilly and Napa, for what it’s worth

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I agree 100%. I once replaced Duralast alternators on my old Jeep 3 times. Lifetime warranty, so they kept giving me new ones! I finally wised up and shelled out for a new one elsewhere.

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If you don’t value your time very highly . . . go ahead and buy those cheapo store brand parts

There is a big hole in the tailpipe in the front side - the part that comes out of the engine. The car is not accelerating properly anymore. Shaking when trying to go faster and very loud. I am no longer getting the P0446 code since I removed the broken solenoid and cleaned it a bit and put it back so I can drive the car. I am waiting for the replacement solenoid to arrive. I am getting 3 codes now. P0440, P0136 and P1441. Are these 2 new codes (P0136 and P1441) related to the hole in the exhaust pipe?

the P0136 could be related to an exhaust leak

The P0446, P0440, P1441 are all related to a leak in the EVAP system

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