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2004 Nissan Frontier CHECK ENGINE light--again!

It seems I have an issue every single year right around inspection time–the check engine light comes on. The site was very helpful last time when the code kept reading O2 sensors–even after they were replaced. A lot of good advice and I finally got it inspected.
This year the code is reading PO442 Evap Code. I tried a few things which didn’t work (new gas cap, etc) and took it to mechanic who replaced gas cap again, Evap Solenoid valve assembly and purge valve, canister. Waited a few days, light came back on. I changed a hose by the evap canister (bypassing a rusty tube) Light came back on in a few days then went off by itself–came back on a day later.
I have had this vehicle for only 3 years and periodically the light will come on for awhile and then go off for no reason a week later. It is costing a bundle every year to keep replacing everything–meanwhile it is running fine.

Is there a chance that the computer system is bad? Any suggestions at all would be very appreciated.
Thank you, Ken


A few questions . . .

Is your mechanic diagnosing your truck . . . or is he just guessing?

If he’s just guessing . . . or incapable of diagnosis . . . you should find somebody else to figure this out

Based on what you said, it sounds like there’s no diagnosis going on

Sounds like he’s taking the shotgun approach. In other words, “throw a bunch of parts at the truck, and hopefully one of those will fix the problem.” That’s not working out too well

Somebody . . . maybe not your current mechanic . . . needs to properly test the evap system

Visual inspection

check for blown fuse(s)

Hook up the evap/smoke machine and check if the truck has a leak, and how big it is

If the machine shows leak, find it and repair it

Check if the purge valve is even capable of pulling a vacuum. If a vacuum hose connecting the purge valve to the intake, for example, is rotten, the valve can’t do its job


One more thing . . . if this guy does not even have an evap/smoke machine at the shop, he’s not the guy for this type of diagnosis/repair

In all likelihood the “computer system” is not the problem. The pcm runs self-tests, when certain parameters allow it to do so. And it apparently doesn’t like what it sees, that’s why that code keeps reoccurring

For example . . . the pcm will only run the evap leak check when you have between 1/4 and 3/4 tank. If you’re near full and empty, forget it

The test will not run if the engine is up to operating temperature

and so on

Thank you for your speedy reply. No, the mechanic wasn’t guessing–The mechanic who looked at the truck initially did hook it up to the evap/smoke machine at his shop and it read a leak at the seal on the purge solenoid that hooked directly to the canister and a leak at gas cap. He replaced Evap Solenoid valve assembly and purge valve, canister and new gas cap. That was the extent of the mechanics work.

Light came on a few days later and that is when I replaced hose (2ft peice connected to canister from back to front and bypassed a metal tube that could have had hole in it) I am trying to resolve this on my own and avoid taking it into a dealer for further work.
Thanks again–I will keep at it.


“Light came on a few days later”

No offense to anybody, but your mechanic apparently didn’t do a complete and thorough job, and here’s why

He CLEARLY did not let the evap monitor run to completion after his repairs and clearing the code

It’s known as “verifying the repair” and it’s one of the most important steps

If he had done it, that check engine light would have come on again for him, and he would have known the repair was in fact not complete

Hmmm…very interesting. This is certainly some useful information–I am not so familiar with what the mechanic would do after a repair. I have been working on my own cars for over 40 years so this is one of the very few times I have had to take any car to the shop.I am still stumped on what to do about this but if I take it to another mechanic at least I know the process–thank you again. Ken


You’re welcome

Whatever you decide to do . . . good luck!

OP might want to read this link, it’s pretty informative, about how car’s evap systems work. There’s a bunch of stuff that can go wrong, and it takes a good deal of expertise to properly diagnose sometimes. Other than perhaps the gas cap, this wouldn’t be an area I’d deal with by parts swapping myself. There’s so many possibilities a person can easily run out of money before running out of ideas.

Thank you for this info–I will definitely read asap.

I had same issue for 3 years…small hole in gas tank did not leak until hole got a little bigger…replaced gas tank no light for over a month…something to think about…tank was rusting away

Gas tank was replaced and as an after thought should have asked to keep the old one and have a look myself. So, it was ok for about a month, got inspected, light is back on. So, here we go again. Inspection due in November and will have to shell out more $$$…just to have someone else try and figure. I keep saying I am getting rid of it once the light stays off—but it doesn’t stay off long enough. I have been disgusted and have not even hooked it up to the meter yet.