Evaporative Emissions System Ghosts

Update: pulled bed and canister and replaced the canister and some hoses, fixed the problem immediately.

So I have a code P0446 that has been driving me crazy, mechanic gave it one simple fix and didn't fix it so I am gonna fix it on my own. Checked the hoses, they all look like they're in good shape. I checked the purge valve (one of two valves on drivers side wheel well) and it clicks on and off fine. Next I plan to pull the bed and look at the canister and related valves. Anything else dumb I should check? How do I know if the charcoal canister is bad?

 

Smoke test it. You can make your own machine. Look on Youtube.
Otherwise, I've had a overflow valve give me fits on a Sienna. It malfunctions and fills the canister with fumes.

The hard thing with the system is that w.o being able to switch the purges on/off manually, you are at the mercy of the ECU going into test mode. Not very often and it takes forever (it seems) to 'ready'.

 

I dont see any reason why you cant use a harbor freight hand vacuum pump to check the integrity of the various lines.

https://www.obd-codes.com/p0446

the explanation(s) is/are pretty straight forward. It would seem that if the vacuum system holds vacuum then it is electrical.

 

have you replaced the gas cap?

 

Toyota Tacoma P0446 Emissions.
https://www.youtube.com/results?search_query=po446+code+on+tacoma

This test is for a Camry PO446 but maye the tips couild help you.
https://www.youtube.com/watch?v=IUHo_nQgDxM

 

I worked on an ex-GF's 2003 Matrix years ago with the same intermittent issue with her emissions test coming up. Took a couple of hours to find it, but it checked out fine after and passed smog without issue. Did all the tests you did and all visual looked fine.
I pulled the EVAP canister and I believe it had two valves on it and I disassembled those to find what appeared to be calcium-like deposits blocking flow from the vacuum lines. Cleaned them out. Be careful with the diaphragm bodies though should you take them apart. Some may come apart, some may not. I think it was labelled a VSV valve from Toyota. Been about 4 years and no EVAP related DTC's returned.

She'd run her tank below 1/4 tank frequently and vehicle sat like this for long periods. Condensation does build up in tanks that aren't filled frequently.

 

I have the same code because my gas tank has a leak. When the gas gets below the halfway point (where the hole is) the tank is no longer pressurized and I get a check engine light. So it seems obvious but check your tank and your gas cap just to make sure

 

I had the p0446 a few years ago and did change the canister. But, the VSV on the canister was probably the problem, not the canister itself. At the time, Toyota did not sell the VSV separately, so I replaced the whole thing (I posted a thread out here on "how to"). The VSV was so corroded it was no wonder that it didn't work. But the canister looked OK-no cracks or holes. I am pretty sure that some time after I came across a replacement VSV for the canister. Last year I had to replace the VSV for evap under the hood. Another corroded mess. Also did a new gas cap. I find those trouble code the most time consuming, and expensive. All good now though.

There is a canister diagnostic in the service manual, or you could have it smoke tested.

 

I pulled the bed, and pulled off the vsv on the canister, tested it and it doesn't even actuate anymore/air barely passes through. So that is an obvious problem, along with some questionable looking hoses. So that means I need to buy a whole new canister in order the replace the valve. I am also gonna replace all the vent lines that run to the canister and the engine bay, what kind of hose should I use (vaccuum or fuel)?

 

You just see smoke better.

 

The charcoal canisters on these trucks are extremely annoying things. Other than the ball joints, this is literally the only other problem I have ever had with this truck.

 

It cleared the code and fixed it and I've been getting better mpgs (not by too much but noticeable).