But failed what? HC NOX CO?
That info tells you where to look for problems.
If I had to guess I would say NOX, but if you failed HC, did you change your
oil before you went in? makes a difference if it's close
NOX is your EGR, formed by fuel burning too fast, back off your timing from stock 1 or 2*
HC is rich and a bad cat, dirty air filter, bad O2 sensor and dirty old engine oil causes that.
same with CO, cat helps to convert that and make sure you test it after getting it hot, and
the cat needs to be hot too, like just got off the freeway hot
Wild