I have a 1999 k1500 5.7L 4wd 124,000 miles. I am getting a SES light and when checked I get a po440. I have had a service center change the vent solenoid, the purge solenoid, smoke test, pressure test, and OEM gas cap and still keep triggering a po44o. You can disconnect the vent solenoid and then re connect it and drive it down the road and the SES light will go out. We have also tightened the plug which connects to the vent solenoid and put dielectric grease on the connectors. It seems as if its something to do with the vent solenoid because the first time we put it on the reader and tried to activate the vent solenoid, it wouldn't click and we took it loose and reconnected it and we got it to click and the light cleared. Now we just un plug it and wait a minute and then re connect it and drive it down the road about a 1/4 mile and it usually goes off. Myself and the service center is at whitts end with this thing. They have finally told me to drive it that way till the part or whatever completely fails. Thats just not a good enough answer. Anyone else have any ideas? They would be greatly appreciated.

Thank you,
Greg A.