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Evap Code P0446

rmb5

By rmb5
in Ask A GM Technician

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rmb5 New Member

rmb5

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2004 silverado 5.3 x cab 4wd. I replaced the vent solonoid and relocated the port near the tranny. then cleared the code and the same code came back. i do not have a reader that can control the vent or the smoke test equip to ck for leaks. which hoses are the likely to be leaking? the hoses connecting to the cannister and also the tank don't appear to be real tight as to pass pressure test. can you induce a few " wc at the vent outlet and soap up the connections to ck for leaks?

 

thanks for any help

bb

minibike132 Senior Enthusiast

minibike132

Posted
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P0446 is not a code that indicates a leak, it indicates a restriction in the system. The restriction would be somewhere between the tank and the vent valve that you already replaced, the most likely suspect is the canister.

rmb5 New Member

rmb5

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P0446 is not a code that indicates a leak, it indicates a restriction in the system. The restriction would be somewhere between the tank and the vent valve that you already replaced, the most likely suspect is the canister.

 

I cked the power to the vent solonoid and was seeing 13vdc with the plug out but unable to hear any click when i plug it in. i'm thinking a bad connection, where is the power fed from. does it do a home run to the pcm? wife always says nothing's ever easy.

 

thanks again for the help

minibike132 Senior Enthusiast

minibike132

Posted
Posted
P0446 is not a code that indicates a leak, it indicates a restriction in the system. The restriction would be somewhere between the tank and the vent valve that you already replaced, the most likely suspect is the canister.

 

I cked the power to the vent solonoid and was seeing 13vdc with the plug out but unable to hear any click when i plug it in. i'm thinking a bad connection, where is the power fed from. does it do a home run to the pcm? wife always says nothing's ever easy.

 

thanks again for the help

 

 

Ignore the valve and the wiring to it, that isn't your issue. The valve has constant ignition power and is ground controlled. It is a normally open valve meaning with no ground applied by the PCM the valve is open. Since the code you have is for a restriction and you have replaced the valve that isn't the issue, unless the ground side was shorted to ground in which case you would have a valve that was constantly closed. However this scenario should set another code.

 

I explained the system with some rough diagrams here http://www.gm-trucks.com/forums/index.php?...c=104569&hl= give it a look it might help you understand what goes on in the system.

rmb5 New Member

rmb5

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What else could be a possible restriction? I have changed the canister and still pulling the 0446 code. Is the tank pressure sensor a factor or does that trip a different code? I did see sparkstech's post about the evap sys and it helped clear up the system piping.

 

thanks again for the help.

bob

minibike132 Senior Enthusiast

minibike132

Posted
Posted
What else could be a possible restriction? I have changed the canister and still pulling the 0446 code. Is the tank pressure sensor a factor or does that trip a different code? I did see sparkstech's post about the evap sys and it helped clear up the system piping.

 

thanks again for the help.

bob

 

The sensor is a factor, it may or may not throw another code. If the sensor is slow to respond to the requested vacuum loss the code would set. If wiring to the sensor were the issue it should set one of a few differnt codes then the one you have.

 

Imo at this point you are spending more money throwing parts at this that having someone that is comfortable with evap diagnosis checking this out and getting it right the first time.

 

Here are the things that can cause it, sensor slow to respond, restriction from the tank to the canister, the canister itself, restriction from the canister to the vent valve, the vent valve itself or a partially stuck open purge valve causing vacuum to be applied to the system when it isn't requested. Oh and the other thing is something you can't do anything about yourself, improper PCM calibrations, I don't see any for this particular code but sometimes the calibrations don't list everything they are intended to fix.

  • 4 weeks later...
rmb5 New Member

rmb5

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following up on the repair. the fuel tank pressure sensor proved to be the problem. is seems that this would have been a code about the sensor.

 

thanks again for the help.

bb

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