My relative has a Mirage circa 2000 with a "Service engine soon" light. He showed it to his mechanic and he said that he doesn't know what is wrong with it and that the car needs to be taken to the dealership because the computer is probably broken. When I popped the hood broken, I immediately saw that a hose is disconnected from the engine and when the car is running it is making hissing sounds. I have no idea what this hose is but it is clearly visible in this picture: http://i7.photobucket.com/albums/y260/Isisdivine/CIMG2161.jpg (right of the oil cap) So the questions are:
1) what is this hose?
2) did the mechanic miss it or does he know what he's doing and this hose is unlikely to result in "check engine" light going off?