You are definitely right. My 300ce failed smog, high NOx. Plugged tube, that is, gives me a code 16 which was an ongoing problem for a long time. I simply was too lazy to get onto it. Resetting the code was a lot easier.
I am using a home made rooter to clean the tube, as some members suggested here. I don't think it a job too bad. In fact, the FAIL part of my smog hurts my esteem, a lot more than my back
.