Sonata 2000 2.5 V6 Auto - Excess CO2 emission. What likely causes?

[Peter]

Sonata 2000 2.5 V6 Auto (UK)

My car has just been checked on a gas analyser and found to have
excess CO2 emission. Level detected 1.2%

Can anyone inform me of the likely cause of this?

 

[hyundaitech]

That's insufficient CO2. Exhaust leak?

 

[Peter]

That's insufficient CO2. Exhaust leak?

Sorry, I meant CO

 

[Peter]

That's insufficient CO2. Exhaust leak?

I meant my car has excess CO. Does your answer still apply?

 

[hyundaitech]

Nope.
Check engine lamp on?
Was the vehicle properly warmed up prior to test?

 

[Peter]

Check engine lamp on?

Was the vehicle properly warmed up prior to test?

I am not sure what the 'engine lamp' is but there are no warnings on
the dashboard.

The excess emission was detected in a UK MOT test and the engine had
been warmed prior to that test.