> The failure was for high HOx levels. 1057 was the limit and she was at
> 1345 (from memory)
HOx isn't one of the tests, it must have been either NOx (nitrogen oxides) or HC
(hydrocarbons). A NOx failure indicates the EGR valve isn't working (bad valve,
plugged passages, broken/cracked vacuum line, etc.) or possibly engine knock
(due to advanced ignition or poor fuel). Might be a cat failure if your engine
has a "3-way" cat.
High HC (without other failures) generally indicates the engine is misfiring due
to poor ignition or whatever (lean mixture if CO is unusually low), but might
also indicate the cat is bad. High HC will eventually make the cat fail from
overheating, so it may be bad now even if it's not the root problem.