Five auto makers maintain secret warranties for repairs of unannounced defects covering at least 30 million cars and light trucks manufactured from 1980 to 1986, the Center for Auto Safety said in Washington. Under such programs, the manufacturer will pay for repairs when owners complain but makes no announcement of the defect or the program, the consumer group said. The five identified by the group--General Motors Corp., Ford Motor Co., Chrysler Corp., American Honda Motor Co. and Toyota Motor Sales U.S.A. Ind.--denied having secret warranties. One charged the center with trying to generate lawsuits for lawyers who are its clients.