The batsman said that "increasing demands" on his body were behind his decision to retire from the limited-overs form of the game on Thursday.
Vaughan now believes that the 31-year-old should clear up his future with the England hierarchy.
"If I was a member of the England management I would want a written promise from Kevin Pietersen that he is committed to playing in the next two Ashes series," he told The Telegraph.
"I would want to know that he is not going to suddenly have another great IPL season, make a load more money and then pull the plug on his Test career in the lead-up to next summer's Ashes.
"If he has got any thoughts of quitting Tests in the next 12 months he has to be honest and tell Andrew Strauss and Andy Flower now, so they have time to bed in someone else. Personally, I think he is committed to Test cricket and the Ashes. He loves Test cricket. It gives him a buzz."
ECB managing director Hugh Morris said on Thursday that he was disappointed with Pietersen's announcement.