High CO reading on Almera

dooroy

I maintain a 2007 Almera 1.5 petrol for a friend of mine whose daughter uses it mostly.
Went for NCT 2 days ago and everything was fine except for the (dreaded) emissions.
I didn't get to see the report yet but over the phone he told me it failed on just one reading : CO (high idle) was 0.50 but the pass was 0.20.
All other readings were within tolerance.
Would this point to one cause or are there a number of possibilities ?
I generally avoid emission problems but as this is a student's car I was hoping to get some info on how it could be sorted.
Thanks for looking.

BOSTIK

Very hard to guess without the full readings but the catalytic converter would appear to be struggling.

Check the plugs first, see what sort of nick they're in. Any idea if it's been serviced recently?

dooroy

Thanks for reply.
Will get the readings and put them up.
Plugs were changed the day before the test , oil and filter about 2 wks earlier .