P0442 & P0446 Let me tell you what I've done first. Any help from you dealership guys will be great

CEL comes one every three days after I clear the DTC's I borrowed my friends smoke machine, hooked it up, clamped off the vent leading to the filler pipe and began smoke testing. Smoke was seen at the fuel filler neck so I then installed the gas cap and continued filling with smoke. This particular smoke machine safety vents at 2psi. I looked with every light imaginable for hours. No smoke anywhere. I let it sit with 2psi in the gas tank for two hours, came back and opened the gas cap and it was venting the smoke and pressure. So, It will hold pressure, but Ive not checked to see if it would hold vacuum. I have an outdated snap-on solus but cant seem to find a fuel tank pressure pid. What exactly should I do next? I have visually inspected all the lines and the canister, then rechecked. Any common problems with these trucks?

 

I had 441, 442, 446. I replaced the VSV on the Charcoal canister and the CEL has stayed off for about a week now. It's a pain in the ass to chase down the culprit.

 

Seems to be something with the secondary air injection switching valve and a by-pass kit that can replace it. Edit: Maybe this isn't the post for the fix https://www.tacomaworld.com/posts/11552044/ Hopefully someone can find the thread

 

Oooh.... I remember this exact thing on a 2003 Matrix I worked on for a GF. She had an emissions test due and had the exact same codes. When I pulled the canister unit along with the valve assembly attached to it, I saw nothing wrong externally and cleared the codes initially, and like you, it returned a few days later!

What I did the second time was visually inspect everything in the system and saw nothing wrong. Then I figured I would take the valve assembly apart and inspected that. Sure enough, that's what the problem was, but it was over $200 for the Matrix to replace it. What I saw was a lot of calcification and what looked like clogged arteries inside the valve/ solenoid units. This is once you pull the vacuum lines off and inspect. They were even lining the hoses! I cleared those out and used compressed air to help clean some of it out after probing and loosening with a needle or a small pick. Don't apply too much pressure on the solenoids (if there are any) themselves though as you can damage them.

I'm sure the system's moisture had become trapped inside and calcified. It was the same white powdery stuff you see around any long term constant water leak and evaporation. Her car was 19 years old at the time. After our 30 mile drive to have the OBD system relearn after a DTC error clear, the car had no more issues at all and it's been good ever since.

Hope this gives you some insight on where to look.

 

had the same issue on a 2002 taco pre 2.7 and after replacing the VSV it cleared out. i got it on Amazon $33.

 

I had same issues, did the cheap things first and sent good money after bad. Turned out to be pin hole in top of fuel tank. Same as having a loose gas cap. Had to replace fuel tank as total corrosion at straps... N. E. 168,000 miles. If you can smoke check tank as the gasket at rollover valve can develop a hairline crack you can't see and this will prevent a VAC on fuel tank as well. Good Luck.

 

I'm a pretty good technician on ford vehicles. I love my yota but this evap system is driving me crazy. Think I'm going to start from scratch and familiarize myself with what each component does and when. Maybe I will have better luck then. I have read an article somewhere saying that if a leak couldn't be fount to replace the fuel filler pipe/roll over valve assembly. Like you said, it maybe cracked