The purpose of the camshaft sensor is to measure the exact position and speed of the camshaft, which allows the engine computer to know exactly when to inject fuel into the cylinder, and open the valve to let air in. If this sensor goes bad or is unplugged, your cam phaser won’t work properly, and you’ll notice engine misfires, startle, and low millage. If your car's check engine lights come on and stay on, more than likely the camshaft sensor is bad.