P0456 - in deep and still no answer!

Disclaimer - I'm not much with a wrench, so I've needed to lean on professional help with my mechanical work.

Backstory 2010 DCLB 6 cyl 3.4L 4x4 224k miles. About 6 years ago it started throwing a P0456 code, seemingly related to wet conditions. After things dried out and a few days later, the check engine light would cycle off. About 6 months ago it threw the same P0456 code but the check engine light never cycled off. Took it to shop #1 where they replaced the leak detection pump and fuel vapor canister and stuck on a generic gas cap. About 2 weeks later the check engine light was back on. I replaced the generic gas cap with an OEM cap, reset the check engine light and it was back in a week. Took it to shop #2 where they ran the diagnostics (smoke test), couldn't pinpoint anything and advised me to drive it as-is and just tolerate the check engine light, since the cost of finding the problem could greatly exceed the cost of actual repair. After scouring TW for additional ideas, as a last resort, I cleaned the gas cap and filler tube and even added a little grease to create a complete seal. Reset the check engine light but it's back again.

Today Open to any/all suggestions for solving the problem within the scope of my abilities and finances. Worst case scenario, wondering if there's any way to safely override the check engine light, b/c that little thing is BOTHERING me! (Note - anytime the check engine light comes on, so does the traction control light immediately below it)

 

That code is hard to find.
But look at the areas where vacuum can leak.

1. Gas cap
2. Hoses
3. Vent valve
4. Purge valve

The vent valve is in the canister, and replaced the canister. So let’s check that off our list.
You replaced the gas cap. Mark that off the list too.

So we’re left with the purge valve and lines.
The purge valve is under the hood. With the engine running, You can disconnect the electrical connector and hose and see if you are drawing any vacuum. Since your code is for a small leak. It can be hard to tell just by listening/looking. You could rig up a vacuum gauge and hook it to the valve (where the hose from the evap canister goes) and see if you are drawing a vacuum. You should not be drawing any vacuum. (Remember, unhook the electrical connection. This closes the valve)

 

If it’s not the purge valve, you might take a scan tool and close the vent valve.
Then smoke test the lines back to the canister.

@Dm93 might know a better way, but I don’t.
Those small leaks can be stupid hard to find sometimes.

 

How do you have a 2010 3.4 v6?

And i found this googling the code you provided.

https://www.tacomaworld.com/threads/code-p0456-fixed.686932/

 

He already tried that. And some…….
He’s half way through the parts cannon.
At some point, you figure it out or give up.
Or replace it all and hope you get lucky.

P045x is a pain in the ass.
I understand the concept, but it’s some more emissions BS to deal with.

 

never double click at the fuel pump. It ruins EVAP.

verify gas cap works.
Testing can include making sure software is up to date, checking TSB’s, vacuum gauge, and smoke test.

I’ve seen EVAP testing done with a tube and bottle hooked up to gas cap overnight. Never done it myself yet so I’m not sure what that test is.

diagnosis is generally better than shotgunning parts but not always. Because parts wear out and dealership diag fee is $230+. If a part such as valve is much cheaper than that, it can be easier to just throw that at it and see what happens.
Including clear codes when done and re evaluate. It takes time for the system to re check itself.

 

You have to physically block the vent at the Leak Detection Pump/Canister to do a proper smoke/pressure test, closing the "vent valve" does not close the system.

Very small (as small as 0.02in orifice equivalent) leaks an be very difficult to find, a smoke machine with a flow meter on it tells you how big of a leak you have although finding the smoke coming out of that small of a leak can be very difficult. I typically can smell the fuel vapors from the leak before I find the smoke.
The purge valve is very easy to test, simply unplug the line from the tank side vacuum port and the electrical connector and start the engine (note this may set a circuit code for the valve). If there's any vacuum present at the port on the valve it's leaking.

 

Be sure to check the top of the gas tank. Large rubber gasket under fuel pump flange and several hose connections that can leak. Can also be a faulty tank pressure sensor, though that usually produces a large leak code. The hose clamp on the rubber hose connecting tank to filler neck can loosen over time. Fought this for days on my sons Silverado. Finally gave up. Smoked it three times and never saw the smoke . Took. Buying three different fuel caps to get one that didn't leak. Horrific quality control on those.

 

Thanks everyone...looks like i've got my homework cut out for me this weekend!

 

@TacoTuesday1 What do you mean by this?

 

when filling a vehicle with gas, the pump clicks off when done. When it is operating normally. The tank is full.

any random gas station usually a crowd of people ignoring this and ruining their vehicle/causing damage by continuing to run the pump (causing it to click more) to put too much fuel.

this saturates with fuel components that are not supposed to be, destroying them, resulting in issues, and complicated expensive replacement.

 

That's what I thought you were talking about...just wanted to verify. Thanks!

 

You don't have the 3.4 if it is a 2010. It is either the 4.0 V6 or the 2.7 I4.

 

honestly regarding smoke test
They have come out with small portable tools but they’re still pricey at $200-300+.

unless you get it, use it once, then hope someone else will buy it off you.

a bit more justified if a tool to buy if you own a cheap old German car that has issues all the time including being made of a million plastic and rubber hoses tubes and valves.

only one I’ve used was an expensive shop tester that had a large tank of nitrogen (inert gas), smoke adder, electric powered to run the smoke.
And even that could still take a while of sending in smoke to actually see it come out anywhere.

It could be similar to MIG gas 75/25 but cheaper being 100 nitrogen and no argon.

never tried zip tieing the smoke on to walk away, don’t want to overpressure the system

I’m not sure if they’ve come out with any UV tools similar to how you can add dye to AC refrigerant or even motor oil to inspect for leaks with a UV flashlight ($30) and yellow UV glasses (also protects your eyes from using the UV)

I’ve heard stories of old school mechanic tricks like blowing cigar smoke to test but 1. It’s a big system to fill with some pressure and smoke, and 2. Lighting a cigar near fuel vapor is not good

 

@Marshall R @harrytasker - my apologies My old T100 was a 3.4L. Yes...this Taco is a 4.0L

 

Thinking out loud. I wonder if you could use a gas like propane or acetylene and a gas detector like whats used for confined space entry. Those gas detectors aren’t too expensive and they’re very sensitive.

Like I said, thinking out loud , don’t blow it up.

 

@Waasheem I like the out-of-the-box thinking. However, this idea absolutely terrifies me

 

There’s a limit to how much pressure can go into the fuel system without damage.
The benefit of an inert gas is its inert. It can prevent breathing but only in large use in a confined space.

versus flammable propane if there is any electrical activity nearby will ignite it.

 

@JonnyAppleseed I just went through this same misery with P0456. I replaced the gas cap, replaced the purge valve, did the smoke test with NO leaks. Turned out to be the charcoal canister. If you do have to replace it, be sure to remove the spare tire to make your life easier. Good luck!

 

He said he already replaced the canister.