P0456 but no leak via smoke test

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Joined
Sep 18, 2019
Messages
580
Location
Mississippi Gulf Coast
I have the Toyota Four Horsemen lights (Check Engine, Skid, TRAC OFF, VSC OFF). OBD code is P0456 (very small leak). Purge VSV valve is closed and doesn't leak via a vacuum gauge and smoke test. I closed the system by plugging the filter exhaust (beyond the Vent valve, see red line) and ran a smoke test. Smoke test boundary was from the red line to the PCV valve at the front of the car. System passed the smoke test, there was no leak. Anyone encounter this? Could it be the vent valve leaking? How do you command the vent valve to close without a scanner tool? Can you back pin the canister pump module harness?

smoke test boundary.png
 
Triple check the gas cap.

do you top off the tank? May have saturated the canister.
 
It’s not the gas cap. New o-ring, then new toyota cap. and there was no smoke Coming from it. Car is new to us. This DTC has been here since we bought it.
 
Last edited:
Ha! I copied this from that conversation @iwashmycar linked to:

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.
 
The 4Runner thread was enlightening, but I am not positive of the pinout on the harness. When I have a moment I can pull the canister and see if I can isolate the vent valve. I think it is the vent valve or the pressure sensor, both of which reside in or attached to the canister module.
 
I wanted to update this thread with where I am so far on this. After this was posted, I checked the purge valve with a vacuum test, which it passed.

I took the car to a local shop where the owner and lead mechanic is a former 20 year Toyota master technician. he also did a smoke test and could not see the leak. He also checked the purge valve. He admitted his scan tool was not as capable as Techstream, but he believes he identified the issue to be within the evap canister. So I replaced the evap canister. No change, the lights came back.

Then I took the car to Allen Toyota where the tech validated everything I had done so far was per the TIS trouble shooting process, and noticed that the gas cap has some condensation on it, which to him meant that the leak was at the fill neck. He tried a new gas cap, no change. So his diagnosis was that the fill neck needed to be replaced. To test this theory, I ran the car for an entire tank full of gas with a rubber glove under the gas cap so that the glove was like a seal. No lights. Progress.

So I replace the fill neck. Now to do this, you need to remove the evap canister. There are two connections on the evap canister, one to the top of the fuel tank and one to the PCV valve. The PCV valve one has this rather weird fitting.

Fill neck goes in, lights come back on. Now I'm perplexed. Did I mess up a fitting somewhere? The vacuum pressures generated in the test are quite low. like between -1 and -5 kPa. That is less than 1 psi. I'm aware that the hoses in the car are mostly 16 years old, so maybe there is an old hose barely leaking somewhere. So I buy a tube of Dupont High Vacuum silicone grease and grease up all the hose barbs, O-rings, etc. for the hoses I have removed. No change, lights come back on.

At this point I am getting desperate. The car is driven by my 16 year old daughter, and a rear wheel drive short wheelbase car designed to have a functioning traction control system driven by an inexperienced driver spells trouble. She complained of the rear end breaking loose a few times, sometimes in traffic. So if this doesn't get fixed, the car is getting sold.

I try taping the little plenum that feeds the PCV valve, thinking there could be a leak where the plenum is split in half. No change.

I keep coming back to the fact that the problem was solved with the glove test before I replaced the fill neck. So it had to be something related to that. I had removed a bunch of hoses to get that in. The Evap canister PCV valve connection came back to me. Could that be leaking? Problem is, that line goes all the way to the engine bay. Replacing that entire line would be a major effort. Fuel tank would need to come down, all the heat shields, etc.

So I cut a bicycle inner tube into a 6 inch section and slipped it over the connection. Then I put 4 or so zip ties on each side to cinch it down super tight. Its been about 6 or so key cycles and no lights. Fingers crossed, knocking on wood, etc.
 
Lights came back on. I've ordered a purge valve. We'll see what that does. The entire internet says that and the gas cap are the problem. Even though I have tested the purge valve with a vacuum test, the internet says they can be intermittent. The car does have 211k on it, so I suppose anything is possible.

I love the part of car repair where you are just throwing parts at it in a series of Hail Mary passes. Hope as a strategy.
 
No change. I’ve even re-run the line from the canister to the purge valve. No change. I’ve given up. Next step would be to drop the tank.

Since there continues to be no smoke, I think it might be an electrical glitch. Some harness somewhere.
 
No change. I’ve even re-run the line from the canister to the purge valve. No change. I’ve given up. Next step would be to drop the tank.

Since there continues to be no smoke, I think it might be an electrical glitch. Some harness somewhere.

before you drop the tank i would check the harness to make sure that there isnt any corrosion and do some continuity checks on the harness, if thats all good i would go with a charcoal canister. they can fail internally and cause a p0456 while still passing the smoke test.
 
before you drop the tank i would check the harness to make sure that there isnt any corrosion and do some continuity checks on the harness, if thats all good i would go with a charcoal canister. they can fail internally and cause a p0456 while still passing the smoke test.
Canister has been replaced
 
check the harness, check the tank and at that point if there isnt any issues found it may be an ecu. before going for a computer i would try to rule everything else out
 
Any updates on this thread? I have a very similar issue and have follow the same troubleshooting steps.. Light continues to come back on!
 
No update. I gave up. The car has been sold.
 

Users who are viewing this thread

Back
Top Bottom