Michael Anderson

I have a 2001 GMC Sierra 1500 with this problem. I created an account just to answer it because I was unable to pass secondary air and it drove me nearly out of my mind. I had two problems that I had to correct in order to get my secondary smog to pass. Took me 3 months to figure out. The process I went through was as follows. Hope it helps someone else that cant afford a new truck. In case you dont want to read details below. Make sure air is getting into your exhaust pipes, and then take it to the dealer for new smog software. My detailed process is as follows: 1. Checked to make sure the secondary air motor was working and turning on at a cold engine start. It only runs for the first 3 minutes after a cold start. I could hear the motor turning on and off. 2. Removed the secondary air lines connected to the exhaust pipes to see if they had blowing air. 3. I started the engine cold and noticed no air was coming out. 4. Worked my way back to the air source so I replaced the check valves just in case ($30 each on amazon). If you do this make sure you remove the metal lines completely and soak threads with WD40 since the valves are really hard to remove. 5. Waited a day and then checked to see if any air was coming out of the large valve located right after the secondary air motor. This is not the check valves. It is another valve that prevents exhaust from blowing into the fan motor. This valve is controlled by a vacuum line. I noticed that no air was getting past this valve. 6. Checked the vacuum line that opens this valve. It is connected to the manifold. I noticed it was completely rotten with a big hole. I was pretty sure this was my problem and wished I had seen earlier. I replaced this with some rubber tubing I had laying around. 7. Did another cold start test and the valve now opened. So air is for sure getting pushed into the exhaust pipes. 8. Drove for month figuring it would eventually pass secondary air but it never happened. 9. Grabbed an OBD monitor and reset everything. Did the famous "drive test" and drove hundreds of miles. Everything else passed except my darn secondary air. 10. Gave up and took it to the dealer for an assessment. They said a lot of people were having problems and that it may just need new smog software downloaded to the cars computer. 11. They charged me $150 for an evaluation. The next day they called and said all smog tests were passing. They claim they didnt do anything, but Im pretty sure they downloaded new smog software. 12. Took it back to the "smog only" shop (have to do this in california) and the guy laughed and said the dealer just charged me for updated the smog software and that they are supposed to do this for free.