The new oxygen sensors helped but did not fix the problem, after six months and 10K miles my P0410 reappeared last week.

After further testing of the air switch over valve and recirculation motor showed no problems with either component I decided to remove the air injection check valve. Access to the valve is not easy and after about 45 minutes, and no success, I decided to try to remove the valve by removing the stainless steel tube that the valve is threaded into - the other end of this tube terminates with a connection into the engine block. From that point I'd guess the air is routed into the exhaust port via internal passages in the engine block.

At any rate removing the tube (with the check valve still attached) was very easy and in about 5 minutes I had the check valve and line on my bench - if you have to remove the check valve save yourself 40 minutes and just remove the tube/valve assembly.

The check valve and tube were 90% clogged by a black carbon based dirt/dust that had accumulated in the line between the check valve and the block. The check valve itself was also very clogged with carbon and soot - I'd guess there were at least 1-2 ounces of loose crap in the line and valve. Given the amount of junk in the line its amazing the air injection sytem worked at all.

I'm pretty sure this was my problem - but I'll update this post again if my latest efforts don't resolve this issue.

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