Mr Lopez, the Spaniard hired by Jack Smith, GM's chief executive, to cut the car maker's huge purchasing costs, first announced last Thursday that he planned to leave to take a senior position at Volkswagen, only to reverse his decision over the weekend.
Mr Lopez, known for near-missionary zeal in excising waste, was apparently lured back with the promise of a five-year dollars 20m contract, and a new title as president of GM's North American operations.
But an hour before a GM press conference scheduled to announce the coup yesterday, Mr Smith received a handwritten note from Mr Lopez, 52, saying he was resigning after all - for reasons that were 'strictly personal', the chief executive said.
'I had intended to announce that Inaki (Mr Lopez) was staying on,' an embarrassed Mr Smith told assembled journalists. 'This morning, everything appeared to be on schedule. At approximately 1pm today, a friend of Mr Lopez delivered a handwritten note from him saying again he was resigning from GM. There was no further explanation.'
No one was quite certain whether Mr Lopez would now end up with Volkswagen, which announced on Sunday that his nomination as head of worldwide production had been 'delayed' by GM's interference.