I'm thinking I'm going to have to pull the exhaust manifold on the wife's Equinox. We've had a P0411 code (secondary air injection incorrect flow) for about a year now, and from testing with a bidirectional scan tool, I can confirm the air pressure when the pump is running is just a little higher than the threshold that trips the P0411, and both check valves are working. There's a TSB detailing that the air injection ports get clogged with carbon, and the manifold has to come off the clean them. The TSB mentions GM Top Engine cleaner, but doesn't really say how to use it. Is there something more readily available? I'm thinking the way to do it is rotate the engine until the exhaust valves are closed, spray the stuff in the ports, break it up with dental pick, and blow it out with air. Sound about right? Would something like Seafoam or something generic clean it up?