Engine check warning light

[CMF_aja007]

My Micra's engine check warning has been on constantly for about two weeks now, although it went off for a few hours after the car had been serviced last week. Apart from the warning light being on constantly, the car is now only getting c.22mpg instead of it's usual c.38mpg.

Has anyone any ideas what the cause could be? The garage suggests it could be the cat be I've been advised this is unlikely.

BTW the car is a 2004 1.2 SE automatic with 50,000 miles on the clock.

 

[CMF_frank2]

you need to check for any faultcodes first really aja (£25 ebay codereader maybe), hopefully its only a lambda sensor and not the notorous chain eh !