I have a 2000 silverado 2500. I got the code 449 so I replaced the vent valve/ solenoid cleared the code it stayed off for about an hour and came back on. I put a smoke machine on the truck and this is where i get confused. With the key on engine off the solenoid is closed and i can not blow through it. So with the smoke I can't find a leak anywhere. It seems to be sealed.

 

P0449 refers to the control circuit for the solenoid. It receives system voltage on the pink wire with the key in run. The PCM controls it on the ground side - if it’s getting system voltage on the pink wire, suspect an open or high resistance on the white wire leading back to the PCM.

 

Thanks I'll check that