Code P0456 - When its not the gas cap

[Elan750]

Well a few days after buying my 4runner, I got the check engine light with the traction control/VSC OFF/ one other light. Read the code and got:

P0456 EVAP Control System Leak Detected Very Small Leak .020"

Most will tell you to change the gas cap, reset the ECU, and voila! Well I got a new Toyota cap and the lights came on a few days later. I then made sure to click the cap 5x., reset the ECU, and the lights came on again a few days later. I've been doing a lot of research on the EVAP system and troubleshooting, so I thought I would make a post to help anyone else that runs into my issue.

Note that I'm a cheapskate so Im not willing to dish out $700+ dollars for a mechanic to fix this. In fact, I refuse to pay more than $100 to fix this problem.

this post is a work in progress.

First, the system:

The lowdown:

Gas naturally gives off fumes and builds pressure in the fuel tank. Too much pressure would be bad, so Toyota deals with it in two ways:

1: when the truck is running, the fumes are directed into the engine intake to burn off. It does by opening the purge valve and the engine intake sucks the fumes into the engine.

2: when the truck isn't running, the fumes are directed through the charcoal canister (cleans the fumes) and then let into the atmosphere through the VSV valve on the canister.

Seems simple right? Well then there is the "periodic test". The ECU wants to make sure the there are no leaks in this system. So a little pump makes vacuum in the system after the vehicle has been off for a number of hours. It them measures if there is any drop in vacuum pressure within the system within 10 minutes. If the vacuum pressure drops, the check engine light comes on.

 

[Elan750]

first I check the purge valve and hoses. They are easily accessible on the drivers side of the engine.

if you blow into it, air should not move because its naturally a closed valve. But hook up a 9v battery to the prongs and you will hear a click, and the valve is in open state. You should be able to blow through it at that point.

the hoses had some cracking at the ends so I replaced the hose with some standard hose I had laying around.

Later, I will use a vacuum gun ($20 bucks at harbor freight) to make sure zero air is travelling past it.

all checks out and I'm on to the canister.....

 

[Starman52]

I'm gonna be following this, I'm having the same problem

 

[ncpinz]

Nice diagram. My son's threw two codes: P0441 and P0455. I'm getting him to pick up a gas cap first. If we still get the codes, we'll start down this path. That diagram helps get our brains wrapped around the system. Thanks.

 

[Stone618]

Good luck! when I bought my truck it had the lights on so the dealer agreed to fix it as a condition to buy the truck. After 5 months and several rental cars later, it was an electrical issue. I don't exactly the issue, but I did find some solder material under the dash by the fuse box area. they replaced the tank, all hoses, charcoal canister. That's just what I know for sure. they would give it back to me and the light would come on the next day. this happened about 5 times. Each time they had the truck for about 2 weeks. At the end they wanted to trade me out of it as a bad deal, but I said give it one more try and the mechanic said he waned to go one more time. That's when they said it was an electrical issue. For all I know they could have bypassed the system. I don't really care because its been several months now and I haven't had the light come back.

check electrical.

 

[Elan750]

Good luck! when I bought my truck it had the lights on so the dealer agreed to fix it as a condition to buy the truck. After 5 months and several rental cars later, it was an electrical issue. I don't exactly the issue, but I did find some solder material under the dash by the fuse box area. they replaced the tank, all hoses, charcoal canister. That's just what I know for sure. they would give it back to me and the light would come on the next day. this happened about 5 times. Each time they had the truck for about 2 weeks. At the end they wanted to trade me out of it as a bad deal, but I said give it one more try and the mechanic said he waned to go one more time. That's when they said it was an electrical issue. For all I know they could have bypassed the system. I don't really care because its been several months now and I haven't had the light come back.

check electrical.

I'll definately keep that in mind. Do you happen to remember the code number?

 

[Stone618]

I'll definately keep that in mind. Do you happen to remember the code number?

I remember it wasn't the same code you had but it was an evap code. it would also jump around to a couple other codes but they were all always an evap code.

 

[Jason Marietta]

Great explanation!

I've been reading a lot of about the Evap system lately too. One mechanic's recommendation was to check the purge and canister vent valves first because they are mechanical and cycled many times. You already checked the purge, maybe check the the canister vent valve? I'm guessing you were headed that way anyway.

Here's the video I found to be most helpful https://www.youtube.com/watch?v=Pg4AEe_xWo4

 

[Elan750]

Made some progress today. First I vacuum tested my new hoses at the engine. This held vacuum perfectly. This also confirms the purge valve is good.

Next I went to the back of the truck where the canister is. I hooked up the vacuum tester to the metal pipe that runs to the engine/purge valve. It also held vacuum!

Next I removed the two large hoses from the canister (IN from gas tank hose, and OUT to atmosphere hose). The small middle hose connects to the previously mentioned pipe(out to engine). I attached my vacuum to the small hose and covered up the 2 big ports with my fingers.(the nipples from where the big hoses attached)annnnnnd no vacuum! There's a leak at the canister. I removed the canister then removed the small middle hose from the canister and hooked up the vacuum directly to the port. Put my fingers back over the large ports annnnd Vacuum!

So there's a steady leak from this small hose, which doesn't surprise me because the clamps have rusted away...

Tomorrow I will replace the hose, reinstall the canister, reset the computer, and see what happens!

 

[Elan750]

Edit: I did test the vacuum of the gas tank too. I had to fill it first so im not trying the vacuum gun all day long. I created vaccum and watched the dial and it was steady. Note the hoses to the gas tank have little o-rings that can be changed. And make sure to snap them all the way back on!

 

[BlackWorksInc]

I can't remember if it was started in '05 or '06 for the 4th gens, but if you have a Techstream you can initiate a self-test of the system as those canisters have a calibrated orifice and will do an automatic self-test. Additionally you can use either a Techstream or a Toyota capable scantool to initiate an EVAP test and watch the vacuum readings on the scantool to essentially do what you're doing as well.

Just some food for thought if you have a scantool and find yourself having EVAP issues.

 

[Elan750]

well its been weeks and no more light!

Anyone who has evap issues, this is a MUST READ:

Be a Toyota leak detective - Automotive Service Professional

The system is more complex that I had thought. It does tests after the car has been off for 5 hours, thats why the light comes on in the morning.

 

[FLynFish]

Elan,

What is the part number for the hose that you ended up replacing? Or did you just buy standard hose and clamps?

Thanks for the details, great thread, and I'm hoping for similar results. I have P0455 and P0441 codes, tried the gas cap to no avail. The purge valve up in the engine bay seems to check good, doing the "suck" test... I couldn't get any leak either direction. SO I'm assuming my problem is either hoses or the canister in the back of the truck.

Thanks again

 

[Elan750]

Elan,

What is the part number for the hose that you ended up replacing? Or did you just buy standard hose and clamps?

Thanks for the details, great thread, and I'm hoping for similar results. I have P0455 and P0441 codes, tried the gas cap to no avail. The purge valve up in the engine bay seems to check good, doing the "suck" test... I couldn't get any leak either direction. SO I'm assuming my problem is either hoses or the canister in the back of the truck.

Thanks again

I just used some standard silicone hose I had laying around.

So you have an 0455 which is "large leak" and 0441 says the purge valve is not functioning correctly(which doesnt necessarily mean the valve is bad, but that the computer isn't recognizing a vacuum change when the valve operates).

You will see the hose coming out of the cannister and running to the purge valve in the front. I would plug in your vaccum there at the canister. That should rule out the front end. Additionally, you might want to grab a 9v battery with some wire and "plug in" the purge solenoid to make sure it clicks open. oyu will hear a click. Air should move freely through it whan it is avtivated.

A gross leak is big, like a hose missing, or valve completely open. Another good test is fill up the gas tank, and unhook the vent hose that travels from the tank to the cannister. get some vacuum in there and see if it holds. This hose has little o-rings on each end that can be replaced too. And make sure it fully clips back in when putting it back. The reason I say to fill up the tank is it will save probably 20 minutes of pumping a handheld vacuum pump!

There is a lot of testing that can be done to the cannister, but I wont go into that until you need to.


Keep me posted!

 

[sunpunkT4R]

Excellent post and maybe just what I was looking for! I'm chasing the same codes p0441 incorrect purge flow, p0455 large leak, & p0456 very small leak. Check engine light, blinking VSC light, & solid on traction light. My codes showed up immediately after replacing the fuel pump. I had ZERO evap issues before fuel pump replacement. Replaced gas cap first. No good. Tried an extra o-ring trick under the cap hoping for better seal. Lights back on in a few days. Took it to a shop for smoke test, they told me the dreaded canister was leaking. Replaced it, cleared codes, put it through rigorous drive cycle, lights back on in a little over a week; however, I got all but one monitor complete and the truck inspected. All monitors are now complete. Called the mech to see if he saw any other leaks or had ideas. He suggested I replace squeeze clips with hose clamps on vac lines before & after the tank vac purge. That did no good either. I can't help but wonder if it may be something with the lock ring for fuel pump? I never have pressure release when removing the gas cap. If I recall correctly, we did not replace a gasket when we replaced the fuel pump. Thoughts?

 

[DezMarius]

Apologies for the resurrection. As with many others I too have the issue with the code. It actually came back this morning. Picked up another gas cap and so far still have it. So am about to embark this path you described above.

Some things I have noticed in my situation.
This seems to happen more often in the cooler months. Which is good b/c I have to get emissions done in the summer. Fortunately have that covered for another year, but it seems that the problem is starting to creep back after a few months off.

Also, my caps never have pressure anymore. I always click them multiple times past. I never get that 'psssh' when opening it up for a refuel. I also never top off.

Makes me wonder if is a problem at the purge valve on the stank being stuck open. Time to get a vacuum pump and get dirty.

 

[sunpunkT4R]

Good luck dude. I still have yet to mess with mine anymore. Life!! Here's a link to another thread I started several months ago about the same (or very similar) issue. Maybe something in there will help as well.

http://www.toyota-4runner.org/4th-gen-t4rs/237593-evap-codes-after-replacing-fuel-pump.html

 

[Miranthis]

Ok, I had a p0456 and reset it after inspecting the gas cap. It came on again this time with P0456, P0455, and P0441. I started with the VSV purge solenoid at the engine bay. It holds vacuum one way but not the other, i.e., putting a vacuum on it from the manifold side it held fine, but putting a vacuum on it from the tank side would not hold more that 12 mmHg and even then it slowly dropped (my MightyVac vacuum pump goes to a bit over 25mmHg).

If i understand correctly, the check routine in the night is for it to close the VSV purge valve (its normal state) and the VSV vent valve at the canister and then create a vacuum in the system. That leaves only the two valves or the gas cap to be obvious leak spots. With the VSV purge not holding a vacuum from the tank side of the line that seems to be the obvious solution.
Or have I missed something

I do note that all the vacuum hoses in the bay are getting brittle and such. Is there any harm in using ordinary vacuum line of the right diameter as opposed to buying the preformed replacement hoses? I will go ahead and do the engine bay and canister connections with new vacuum line if it is not an issue.

 

[AuSeeker]

Ok, I had a p0456 and reset it after inspecting the gas cap. It came on again this time with P0456, P0455, and P0441. I started with the VSV purge solenoid at the engine bay. It holds vacuum one way but not the other, i.e., putting a vacuum on it from the manifold side it held fine, but putting a vacuum on it from the tank side would not hold more that 12 mmHg and even then it slowly dropped (my MightyVac vacuum pump goes to a bit over 25mmHg).

If i understand correctly, the check routine in the night is for it to close the VSV purge valve (its normal state) and the VSV vent valve at the canister and then create a vacuum in the system. That leaves only the two valves or the gas cap to be obvious leak spots. With the VSV purge not holding a vacuum from the tank side of the line that seems to be the obvious solution.
Or have I missed something

I do note that all the vacuum hoses in the bay are getting brittle and such. Is there any harm in using ordinary vacuum line of the right diameter as opposed to buying the preformed replacement hoses? I will go ahead and do the engine bay and canister connections with new vacuum line if it is not an issue.

Jeff you also have a big rubber hose from the gas door/neck and the tank.

 

[Seymore Butts]

Where is the little pump that is used in the self-test? What would happen if you disable this pump and the self-test could not run?