p0449

[nateashfield]

fault code p0449. Already replaced the vent solenoid, verified the solenoid does indeed work, have power at the solenoid but the ground never closes. I know this because I cleared the code and laid underneith the truck with a test light hooked up and waited for the code to show up again.. which it did but the light never lit.. and the light does work. The wiring itself looks fine as far as I could see. So now what is the next step. Is there a relay or something that tells the ground to close... and if so where is it.

[mazdab2600]

this should help in understanding the evap system.

[nateashfield]

Thanks!! it was actually the canister purge valve I replaced.. I'll have to have a look at the vent and see if it is also bad. Just as note if you ever have to replace the canister purge valve it is around $200 but the Hummer H2 has the identical part and it sells for $45.. the only difference is the H2 one doesn't come with a new pipe.. it took me about 14 seconds to pull the old pipe off and re-use it so I figured it was worth the $150 savings.

[nateashfield]

tonight I took off the purge valve tonight and jumped it and it opened up fine.. power to the valve but it never gets the command to open. So now both purge valve and vent valve have been confirmed to work and power is going to both valves so I guess that leaves me with the ground not being closed... which I am now lead to believe is a problem with the pcm. Any thoughts/suggestions.. any way to test the pcm

[mazdab2600]

yes the pcm grounds the solinoids.
need a scan tool to check/force the evap to test itself with the pcm.
but on turning the key on for startup it should run its own self test????
same as many ppl get the loose gas cap code/light.

[ssgjurista]

Originally Posted by nateashfield

tonight I took off the purge valve tonight and jumped it and it opened up fine.. power to the valve but it never gets the command to open. So now both purge valve and vent valve have been confirmed to work and power is going to both valves so I guess that leaves me with the ground not being closed... which I am now lead to believe is a problem with the pcm. Any thoughts/suggestions.. any way to test the pcm

I've been looking over the info that mazdab2600 posted. I would agree that the pcm supplies the ground. You said both the vent solenoid and purge solenoid are getting power.
So after reading up on exactly how the system works, I came up with some possible answers. When the engine is cold and first started the pcm sends a ground to the purge valve so it opens but not the vent solenoid so it stays closed. This creates a vacuum from the throttle body all the way back to the canister. The pcm then closes the purge valve, trapping the vacuum and monitors the fuel pressure sensor. If pressure starts dropping, the pcm thinks it has detected a leak and will set a code.

Once the engine is warmed up, the pcm opens the vent valve and based on signals from the fuel pressure sensor, it opens and closes the purge valve as needed to let the vapors pass to the throttlebody. So here's my suggestions: Carefully inspect the evap tubing from the throttle body to the purge valve and from the purge valve back to the canister for any kind of breaks or even hairline cracks. Once you verify all the tubing is okay, I would suspect the fuel pressure sensor or wiring to it is the cause.

[nateashfield]

well I guess in the morning I'll try to pressurize the system through the test port and spray all the lines and connectors with some soapy water and see what happens.. What will actually set the P0449 code?

[mazdab2600]

just googgled the 0449 code.
found this check for a fuse marked-CNSTR VENT see if its blown???

http://355nation.net/forum/engine-drive ... p0449.html

[ssgjurista]

Originally Posted by nateashfield

well I guess in the morning I'll try to pressurize the system through the test port and spray all the lines and connectors with some soapy water and see what happens.. What will actually set the P0449 code?

A loose or defective gas cap, a vacuum leak in the system, a defective fuel pressure sensor, or the pcm isn't getting a signal from the sensor.

[DYANIK]

I just got the same code last week. It usually starts as a gas cap message on the dash and eventually lights the check engine light. I have cleared it twice and it keeps coming back about 5 minutes into driving. I planned to get a new gas cap but I do no think that is the problem. the truck only has 60k and most of that is highway, Relatively speaking that gas cap has not had many cycles of use....

I am curious how this turns out for you. I think I need an emissions test this summer for plates and need to get rid of that light.