What could be wrong when the check indicator light is on in a Hyundai Accent?

I had my check indicator light on and the first time is was a sensor that controlled the amount of fuel going to the engine, it failed and was starving the engine of fuel. I had to have the sensor replaced (expensive)

Second time it was the Oxygen sensor that goes into the flexible exhaust pipe. The pipe had developed a leak and was causing the sensor to go off. I had the pipe replaced and reset the sensor by disconnecting the battery for an hour or two. It seemed to do the trick but the exhaust guy said the sensor is barely holding in there and will eventually fail.

The MIL (malfunction indicator lamp/check engine light) can be set by anything from a loose gas cap to an engine perfomance issue. If the light is steadily illuminated it can be driven but should be checked out sooner than later. If light is flashing do not drive the vehicle.