04 RX8 engine light on

I've checked everything over and can't see any problems. The oils fine, filters are fine, head should be ok, fuel filler cap is tight, leads and plugs are fine, just had a brand new starter, compression is good, no leaks anywhere, the cat should be fine because acceleration is decent, and the fuel consumption is the same as ever.

Someone said the engine warning light can come on when the cars due a service. Could it just be that?

I don't want to pay garage fees if it's not a problem. Is there anything else I should check before getting it diagnosed?