The anti-pollution alarm, in particular the catalytic convertor alarm, will
come on for any engine fault that causes neat petrol to go down the
exhaust pipe.

The 2L engine has got hydraulic tappets which get a patina after a few years
and make them sluggish in operation. Net result .... the exhaust port is
still
slightly open when the compression stroke comes up, so neat fuel
goes down the exhaust pipe.

The two alarms that you mention result in uninformed mechanics replacing
the catalytic convertor, the ignition coil pack and the injector on the
faulty cylinder, but the cure is to flush the hydraulic tappets before
refilling
with oil.

One long term cure is to replace them with those from the 1.8 engine.