Diagnosing EVAP system codes P0442 and P0456 (2 Viewers)

[chilllx470]

(long post warning)

In my journey to revive my new 2004 LX470, I've got P0442 and P0456 pending codes that are preventing the car from passing emissions. (They eventually turn on the CEL). I'm trying to diagnose the issue in this post and hopefully tap into the collective knowledge of forum.

First thing I did was replace the old gas cap. That didn't help. I physically checked the hoses in the engine bay and around the charcoal canister and could not find any visible issues.

I'm not too familiar with the EVAP system but I tried to diagnose it using Techstream (TS). I'm going to try and list out what I did, and what I think is going on during Techstream's leak test.

First, let's make sure the naming is consistent:
1. Purge valve (or VSV - Vacuum Switching Valve) - This is on the engine (intake) and controls pulling air from the charcoal canister into the engine. This is part number 25860-50100
2. Canister control valve - This is located on the fender and pulls fresh air from the air intake. Part number 90910-12261
3. Tank bypass valve - This one sits on the charcoal canister and is the link between the fuel tank and the charcoal canister.

I checked the individual operation of the purge and canister control valve using TS and they turn on and off just fine. However, with the car running, and the purge valve closed, it would occasionally pull air every few seconds. I checked by disconnecting the hose coming from the canister and putting my finger on the valve. This led me to believe that the purge valve is not sealing correctly.

I got a new purge valve, and that showed the same behavior! With the car running it seems the engine pulls really hard and the purge valve does not stay perfectly sealed. I think this may not be an issue, because the job of the purge valve is to seal the system when the car is off. What do people think? What're the chances that two new purge valves are both faulty?
Oh and the canister control valve does the same thing. With the car running, it also sucks in air every few seconds when closed through TS. Again, this leads me to believe this is normal behavior for both these valves.

Anyways, next I ran the 11-step leak test in TS. I posted the whole video of the test below.
But here are some things that stood out to me:

At step 4, when it's sealing the system (only tank bypass valve open) the value changes from 0.503 to 0.600 over 80 seconds. I am taking this as a rise (opposite of vacuum) in pressure in the tank (as it goes into negative when the purge valve is open, creating vacuum).
The purge and canister valves are closed, and the engine is running. I don't get why this would happen. But maybe this is not an issue...


Step 5 opens the purge valve so it starts developing a vacuum, then in step 6 when the system seals again (only tank bypass valve open) the pressure rises from -10 to 0 in about 120 seconds. This does not seem right to me. Shouldn't the pressure hold consistently? Is this an indication of a leak on the tank bypass valve side?

A similar thing happens on step 8 when whole system is sealed (all three valves closed). The engine is running and pressure is still going up (losing vacuum). Now does this again indicate the tank bypass valve (or the charcoal canister) is leaking?

Step 10 is confusing. It says it's "Isolating Tank" and only the canister control valve is open. Why would that happen when it's isolating the tank? That just pumps air into the charcoal canister, from what I understand.

I'm not sure what the conclusion is from all this, but I have a feeling either the tank bypass valve is leaking, or there's something else on that part of the system. Perhaps the fuel filler line?

Sorry for this long post, but if anything here stands out and makes sense to anyone, then please help!

Here's the video of the test:

 

[JunkCrzr89]

Let’s start simple first: Did you replace the gas cap with a new OEM Toyota cap? Did you inspect the filler tube for cracks? After you replaced the cap, did you clear the DTCs and then run the truck through all the cycles?

 

[chilllx470]

Let’s start simple first: Did you replace the gas cap with a new OEM Toyota cap? Did you inspect the filler tube for cracks? After you replaced the cap, did you clear the DTCs and then run the truck through all the cycles?

I replaced the cap with a generic one from Autozone, and yes cleared the codes after that.
Did not check the filler tube for cracks. I'll do that tomorrow.

 

[yngmrostrvile]

Small leaks can be super challenging to find. Looks like there is some rust on the rig. If you can "smoke" the evap system or apply low pressure compressed air (<5psi) through the fuel filler neck and spray filler neck and hoses with a soaky solution you might find it.
The ecu runs the small leak test after a cold soak. So if you clear the cel and drive, it would normally not re-illuminate until turning vehicle off and driving the next day or hoouurrrs later.

 

[chilllx470]

I got a smoke test done by a shop today. They didn’t find any leaks. Their software showed that the tank bypass valve on the charcoal canister is not active consistently. They said it could be because of the aftermarket cap, and asked me to get an Oem fuel cap first.
Will pick one up tomorrow and check again. It takes a couple of morning starts for the code to show up…
If that doesn’t work then I guess will have to find a new charcoal canister.

 

[dtomala]

I have the same issue that just started on my 2003 470. Since I don’t have an emissions army where I live is there any way to bypass sensors or fool the ecu somehow so my dashboard doesn’t light up like a Christmas tree every time the self test runs. I could really care less if the evap system is leaking, but I do want to know if another code comes in that will actually affect the performance of the rig like an 02 sensor going bad, etc. it’s annoying I gotta reset it every week and it makes my wife and kid nervous driving with a cel on. I got almost 20 years on this rig I might just do some electrical tape magic and just check the codes every oil change. Anyways, thanks for listening.

 

[94SRUNNER]

I got a smoke test done by a shop today. They didn’t find any leaks. Their software showed that the tank bypass valve on the charcoal canister is not active consistently. They said it could be because of the aftermarket cap, and asked me to get an Oem fuel cap first.
Will pick one up tomorrow and check again. It takes a couple of morning starts for the code to show up…
If that doesn’t work then I guess will have to find a new charcoal canister.

I was going to suggest you just pick up an OEM gas cap....did you end up doing that?

Any updates, it has been about 2 months.

 

[94SRUNNER]

I have the same issue that just started on my 2003 470. Since I don’t have an emissions army where I live is there any way to bypass sensors or fool the ecu somehow so my dashboard doesn’t light up like a Christmas tree every time the self test runs. I could really care less if the evap system is leaking, but I do want to know if another code comes in that will actually affect the performance of the rig like an 02 sensor going bad, etc. it’s annoying I gotta reset it every week and it makes my wife and kid nervous driving with a cel on. I got almost 20 years on this rig I might just do some electrical tape magic and just check the codes every oil change. Anyways, thanks for listening.

I have not seen any bypass for the emissions. Have you tried a new gas cap?

What codes are you getting?

 

[dtomala]

I have not seen any bypass for the emissions. Have you tried a new gas cap?

What codes are you getting?

I have the Amazon gas cap and same codes as chillx.

 

[chilllx470]

Update: I installed an OEM cap, and also changed the charcoal canister on suggestion of the mechanic. The codes still show up...

Here's a detail, the old canister was slightly wet on the top when I took it down. What does that mean?

 

[chilllx470]

I have yet to run TS again to see if the behavior is the same with the new canister.

 

[chilllx470]

So I took the car to another shop and had them do a smoke test. Smoke was leaking from the gas filler neck. The tech said it wasn't the cap and they fixed it with some rubber packing. That stopped the leak.
They also replaced a couple of hoses near the canister.

However, after driving for 50 miles the 442 code came back. The 456 seems to be fixed. The tech mentioned if the codes aren't fixed then they might have to take the fuel tank off and replace the hoses from the top. :/
I'm not sure about that but taking it back to the shop and see if they can do some more tests.

 

[chilllx470]

So, took it to the shop again, and they did the tests again, and said the pressure is leaking from the gas cap again. They put some grease on the cap and the tech showed me to press it down and tighten it to get a better seal. After that the tests didn't show any pressure loss. Mind you, this is an OEM cap from Lexus.
Going to drive it for a few days and see if the code comes back.

 

[bozncsurf]

I have the same codes.
Last week I changed the canister hoses / clamps.
Today I changed the charcoal canister / built in sensor.

Fingers crossed.

@chilllx470 Please report back with your findings.

 

[chilllx470]

One more day of driving, put 60 miles on it and the code has not come back.

 

[seanz0rz]

Stuck with the same codes. Shop had it for a week and could not find the issue. Right now I have the two lines going to the engine compartment clamped at the charcoal canister and no more check engine light. I have zero idea what that tells me (still haven't wrapped my head around how the system works.)

I have replaced the cap and canister with OEM.

 

[chilllx470]

The code and CEL came back on.

 

[chilllx470]

Does anyone have ideas on what could be going on? What else can we try? Should I have the shop take down the fuel tank and check?

 

[yngmrostrvile]

You stated that they smoke test revealed the fuel filler neck and "packing" was used to seal. Have you since replaced fuel filler neck? If the filler neck is leaking from rust it is porous...many lil holes. You might fix some with "packing" but more will start to leak. Did you resmoke?
Did you ever apply a bit of compressed air through the filled neck and spray it and hoses between filler amd tank with soapy water solution? When I turned wrenches this was usually how I found small leaks. Block off some of the other components to see if you can narrow things down.

 

[chilllx470]

Actually the tech blames the fuel cap, not the filler neck.
But I think what you mentioned is worth a try.