What is the function of the Air Shutoff Valve and what are the symptoms of a malfunctioning one. Lastly, is there any connection of a faulty shutoff valve and 2ndary air and/or egr OBDII readiness? Thanks.

Are you talking about the air-injection diverter valve? are you getting code P0 411?

Or is readiness the only issue?

EGR readiness is all about vacuum changes in the intake during deceleration.

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Readiness is the issue. No codes (probably because it doesn't achieve readiness). Unfortunately still chasing readiness solution for EGR, 2ndary air, and Catalyst. Just need one to complete and trying to focus on one of them. Unfortunately, something is preventing one and then the other 2 (if they go in sequence) or there is a (or are) enabling criteria not being met for all of them. (Front 02 is new). Tracing the problem as much as possible, the last CE was about a year and half ago with a code 1137. Changed out the post cat O2 sensor (that was the solution the last time I got the code). No CE light since. Of course, that may have been when readiness became an issue. Was 1137 caused by something else and signaled impending doom? Any possible link? 2ndary air pump works at startup. As mentioned I have not heard the 2nd running of the air pump after warmup in a long while.

As always, thanks for your input, MBDoc.