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Okay, I've followed and read through this thread for months. I have a P0446.

I've replaced the vapor canister/vent solenoid, the fuel tank pressure sensor, blew out the line from the vapor canister/vent solenoid into the tank, the purge solenoid, and the gas cap.

p0446 still keeps popping up. Smog test due in a month. I'm about to give up and to go a mechanic unless someone can tell me another possibility.

Any thoughts?
200 Suburban 1500, 230,000 miles
 

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Have you verified the lines for no leaks or blockages? Did you replace the canister or just the solenoid?

Ted
 

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Have you verified the lines for no leaks or blockages? Did you replace the canister or just the solenoid?

Ted
I blew out the line from the canister to the tank, my assumption is that it blew out any blockages. I don't have a smoke machine to check for leaks. Any idea on how to do either/both.

I replaced the canister and the solenoid (same part)
 

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@MilesPup - if your evap hoses are all in good condition then also check:
  • Purge valve solenoid (under hood) - passes air when open and clicks open/closed when given 12V
  • Purge valve solenoid plug - shows 12V when key is on
  • Vent valve solenoid plug (by canister) - shows 12V when key is on
  • Fuel tank pressure sensor plug (top of fuel tank) - shows 5V when key is on between ground and the other two wires
 

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@Jeremy Borum I found your post most useful in diagnosing my problem P0446,

I check the solenoids with a small 12 volt battery to see if they worked properly, and they did.
But there was no 12 volts at the connector to them when I turn the car on.
The Red wire, had power on with the key on, but no ground on the other wire.
I spliced into the ground(other) wire in the harness, and ran it to the frame of the car.
The solenoids work now.
Thank you for that info.
 

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Hi guys, great info in this thread especially because I have a new to me 2005 Chevrolet express AWD that just shot a p0446 code. I have a couple of questions.

What diagnostic computer can I get that can read the data I need to diagnose the P0446? I have already cleaned out the canister/vent and it was not dirty at all. I have a feeling I have something else going on and I see there is a list of things I could check with a diagnostic computer, just want to make sure I get one that can read the right data.

Thanks
 

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Hi guys, great info in this thread especially because I have a new to me 2005 Chevrolet express AWD that just shot a p0446 code. I have a couple of questions.

What diagnostic computer can I get that can read the data I need to diagnose the P0446? I have already cleaned out the canister/vent and it was not dirty at all. I have a feeling I have something else going on and I see there is a list of things I could check with a diagnostic computer, just want to make sure I get one that can read the right data.

Thanks
Try and see if your Vent Solenoid is clicking. By removing it and taking to wires to battery and touch the terminals of the
Vent Solenoid. Also check the pigtail of the connection to the
Vent Solenoid. Mines was all coroded, green powder. So I cut both connection and splice wires togather now everything is working.
 

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2005 Chevrolet Express AWD

Looks like either my fuel pressure sensor in the tank is bad or the wiring is bad. I hooked it up to a scanner and looking at live data, the sensor is stuck at 4.8v or -32 mmHG.

I will get it up on jack stands this week but wanted to see if anyone has done this on an express before? Were you able to reach the sensor without dropping the gas tank?
 

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Just one code...the infamous P0446
so the 446 is a code that the Evap vapor test controlled by the PCM indicates that the vacuum in the fuel tank when testing is taking more than 4 sec for the vacuum to drop of the desired amount.

now the ground wire on the pressure sensor or connector ""a restriction in the venting /canister"" . or a defective in tank pressure sensor , which is a tough job to replace / expensive ..
another possible item is a PCM connector dirty/water/corrosion issue.

the volts 4.8vdc on the sensor output dark green ? black should be ground and gray is the 5voltDC power to the press sensor from PCM

post back how it got resolved ..
 

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so the 446 is a code that the Evap vapor test controlled by the PCM indicates that the vacuum in the fuel tank when testing is taking more than 4 sec for the vacuum to drop of the desired amount.

now the ground wire on the pressure sensor or connector ""a restriction in the venting /canister"" . or a defective in tank pressure sensor , which is a tough job to replace / expensive ..
another possible item is a PCM connector dirty/water/corrosion issue.

the volts 4.8vdc on the sensor output dark green ? black should be ground and gray is the 5voltDC power to the press sensor from PCM

post back how it got resolved ..
That is what I am trying to get to, the wiring. That is why I am asking if I need to drop the tank or can I access wiring by reaching up on top of the tank?

I have seen a bunch of youtube videos but they are mostly for pickups. Nothing for the AWD express. I am hoping I can just reach up and yank the sensor and wiring out to run some tests to see if its the sensor or the wires that are the issue.
 

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That is what I am trying to get to, the wiring. That is why I am asking if I need to drop the tank or can I access wiring by reaching up on top of the tank?

I have seen a bunch of youtube videos but they are mostly for pickups. Nothing for the AWD express. I am hoping I can just reach up and yank the sensor and wiring out to run some tests to see if its the sensor or the wires that are the issue.
sorry but that vehicle you have can be complicated I doubt this procedure will be available from a member , and the tank on suburbans requires tank drop. did you check for an access hole / door to get to the fuel pump inside the vehicle ?
vent valve could be stuck closed or canister plugged .. do you fill the fuel tank to the max then park it ? how long you owned this ? use this on dirt roads ?
 

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a bulletin came out some time after I bought my 2007 GMC 1500 HD Classic 4wd pickup. I had it in for an oil change and was advised that there was a recall bulletin that needed to be done, no charge about 4 hours. Ok, picked it up and drove home. Next morning, over night temp 49 and the check engine light came on after idling for about 4 minutes. I took it back to the dealership, and asked about the recall of the previous day and they showed me a new "purge Canister, and 5/8" hose that was run to the transmission tail area and a little plastic grill. They turned the check engine light off/reset it Code P0446, and could not get it repeated. Next morning same thing. Took it back to the dealer, changed the canister and solenoid again, and told me it was fixed and sent me on my way. Next day, I didn't start the truck until mid afternoon, temp 86 and no light. Two days later, started it in the morning and check engine light on again. Took it back in and was told that it was the same code, but box under the truck bed was causing it, box was $700, and $160 in labor and insisted the problem was fixed. On the way home I stopped at an auto parts store and they had a diagnostics computer $140 so I got it. The next morning, (Saturday) started it up, same light and code. Monday took it back in and was told the box they had to replace had been "really dirty", and must have clogged the sensor on top of the fuel tank. Dropped the fuel tank, replaced the sensor, and said all was good now, and another $900 by the way. When I was called to tell me it was ready for pick up, I said I was busy and would pick it up in the morning. I went over to the dealership at 7:30 when service opens and insisted on having the service manager go with me to get the truck. There was a bit of an argument about that, but I wanted witnesses to the Check Engine light coming on sitting overnight and cool temperatures overnight. She cranked the engine and started to drive up to the service lane and the light came on. They kept the truck for three more days and couldn't find the cause. No fix, and no idea why. A large argument over the whole recall compliance, which finally ended in a decision that it was out of Warranty (36400 miles) and it couldn't be proven that the recall repairs started it all and therefore take your business elsewhere. I have since that time used the meter to clear the codes and just driven it. Its irritating, but only occurs when nights fall below 60 degrees, winter only ghost. Anytime I don't want to deal with it, I start it run it at 2000 rpm until the engine temp gets to the first longer temp line and it never comes on. Anyone got any ideas? I've sent a copy of the service bulletin to GM Customer Service (three time) with copies of the service tickets and asked for help, never a reply. I love the truck, its old like me.
 

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It sounds like they have checked or replaced almost everything in the EVAP system, but you didn't mention anything about the most accessible part. There's a solenoid on the engine which is very accessible, right side top, and perhaps it's misbehaving. See my post in the middle of page 14 for more details.
https://www.gmtruckclub.com/forum/threads/quick-fix-for-code-p0446-evap-emissions-vent-circuit-low.18964/page-14

You might also check the condition of all your vacuum hoses, although I'm sure they did that already.
 

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I have seen mentioned in a couple different articles that a mixture of codes can narrow down your search for the solution,
Such as P0446 with P0420, which is what I have on a 2014 Sierra 1500 5.3L, 100,000 miles. Does anyone know about this combo ?
Thanks
 

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what you did was a very bad decision ... """" which finally ended in a decision that it was out of Warranty (364,000miles)"""...

GM will destroy your truck because they only want the $$$ to force you to dump it..
IMO NEVER BRING AN OLD GM VEHICLE BACK TO THE DEALERSHIP ... ALSO 150k PLUS MILES ON IT END OF LIFE!!!
 
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