I keep getting a P0411 "Secondary Air Injection Improper Flow Detected" code and can't figure out what is causing it. It happens on just about every cold start. So far I have:

-verified fuses and relays are good
-verified the SAS AIR pump runs and draws a suction
-change my air filter more often than needed

My next guess would be to replace the two SAS check valves, but there are no other codes to make me think they are bad. No other codes at all, and no backfiring. What exactly determines if flow is correct or not? Could whatever that is be the problem? Without other codes and other symptoms, I'm at a loss. Any suggestions?

 

Could be an accumulation of carbon residue clogged or constricting the system.

 

How do I remedy that?

 

You will have to manually clean the carbon out by hand. I know of no other way. I've never liked any of the air-injection systems for reasons such as this one. At least with the old A.I.R. belt-driven AIR pump systems, you had the A.I.R. system rails going into the exhaust manifolds, but these new ones go into the exhaust system near the catalytic converters, making it much more difficult. I would never buy a vehicle with any AIR injection system.

Unfortunately, Chevrolet installed it on my late father's 1969 Chevy C-60, 2.5-ton, 366 cubic inch big-block truck, which did not require it. Once I found that out, I took it all off and chucked in the dumpster, and plugged up the manifold holes. That was an expensive lesson as all the dust chewed up SMOG pumps like crazy and well as the diverter valve. Still, I've always been a fan of Chevrolet's, but that was one very costly mistake that I will never make.