John Gapper:

It is an easy error to make. Although much of the technology that guides and controls cars is built by suppliers, even the biggest of them is little known outside the industry. The balance of power, and most of the market value, lies with the “original equipment manufacturers” that assemble vehicles and sell them to consumers.
 But competition is intensifying as Google and Apple enter the market. Google is testing a self-driving car that uses Bosch sensors. No one knows precisely what Apple is doing, but it is employing several hundred people on a project called Titan. Along with Elon Musk’s Tesla, Silicon Valley companies are challenging Detroit.
 The challenge is not merely external. As software and communications become as integral to a new generation of vehicles as hardware, the tradition of OEMs being able to control and squeeze their suppliers is shifting. There is a revolution from below.