The Volt uses an estimated 10 million lines of code, running about 100 control units. That's up from about six million lines of code in typical 2009 model cars and as little as 2.4 million in 2005. Each Volt has its own IP address. "They use it for a few things today, like finding a charging station, but they hope to use it to push more software out to the vehicles in the future," Selfe said. "Software is becoming the most strategic asset and its use is growing astronomically," said Meg Selfe, a vice president for complex and embedded systems at IBM Rational.

http://www.eetimes.com/electronics-news/4215735/IBM-tells-story-behind-Chevy-Volt-design

http://www.youtube.com/watch?v=jMoYNzy210I

Obviously, car repair will require more than mechanical skills going forward.

Does GM own the 10M lines of code? Is there a chance that a competitor could hire IBM for a similar project and benefit from GM's ground-breaking work?

From the article, it seems like GM does own some code as they did do at least some development in house. It seems that IBM's involvement was higher level, as in providing the tools that were used. It does not seem that IBM wrote any code used in the Volt, but that their tools were used to help integrate and generate code. Like using Excel to generate numbers.