High CO level
 

Wife took MY00 for mot last week.
Failed on CO level, about 3.5% running with just centre cat.
Put downpipe cat back on, went for re-test, now CO at 6.8% !!!!
Tester said it might be Lambda sensor, but wasn't sure.
Can anyone help me on this one.
Southend area.
Thanks...
JERRY........

!:mad: !