An EGR that is not opening, will cause elevated NOx readings ( that's what it's there for ).
An EGR that is opening too fast, or not closing properly, would cause elevated HC readings.
I am really interested to see what the outcome of this is, once John goes for his diagnostics on Thursday.
It'll probably turn out to be some kind od " head slapper ".
And yes, you are right as far as an exhaust leak being identified during an emissions test. Air dilution is measured and must be within certain limits.
2007 C 230 Sport.