CARS.COM — Most car owners probably don’t know that their vehicle has a crankshaft position sensor until the engine dies, won’t start or starts running poorly.

Your vehicle's crankshaft sensor can be, well, cranky. But it's also a key part you can't do without. So what makes one fail? And how do you know if it's bad?

I just got my 2010 Ford Escape (a four cylinder) back from the repair shop. It hadn't been starting, and I was told the cause was a broken crankshaft sensor. The repair seems to be successful, and ...