If the malfunction indicator lamp (MIL) is on, the orange lamp with an engine symbol, it means that the Engine Control Module (ECM) has detected a fault with the engine management system relating to emissions, and has stored a fault code/s in respect of that fault. You will need to get the car hooked up to a suitable piece of diagnostic equipment to read them. The warning lamp merely alerts the driver that a fault with the system exists, but it does not tell you what the fault is.

The problem could be many things, and you really cannot guess. If you can get the fault codes read please post them here, and I'm sure many people on here can help. Be aware though in any event you will need diagnostic equipment to clear the codes and extinguish the warning lamp.