Cobalt Group announced Wednesday that it has received a $15 million line of credit from investment firm Warburg Pincus. Cobalt makes e-business software for the automotive retail market that car dealers and manufacturers use on their Web sites. Warburg started investing in Cobalt in 1998 and now holds a majority stake in the Seattle-based company. The firm led a $15 million private-equity investment in Cobalt in June 2000 and invested an additional $34.5 million to take the company private in November 2001. Cobalt went public in August 1999.