A mechanical engineer, an electrical engineer, and a programmer are riding in a car.

The car breaks down and coasts to the side of the road.

"Hang on," says the mechanical engineer. "The problem is probably the engine, let me have a look at it and I'll have us on the road again in no time."

"Wait," says the electrical engineer. "The way it just stopped like that, I think it's the electrical system. Let me have a look and I'll get us going again in a minute or two."

"Hold on," says the computer engineer. "Why don't we all just get out of the car and get in again, and then see if it starts?"

Alternate punchlines:

"Why don't we open and close all the windows, and then see if it starts?"

"Why don't we remove parts from the engine until it starts successfully?"