Prosecutors are also said to be investigating an executive, upper management member and former employee.
Kerner was among three current and former Porsche employees under investigation by German prosecutors for alleged roles in the diesel emissions scandal.
"We reject these allegations and will do our utmost to clear up the matter," Porsche CEO Oliver Blume wrote this week in a memo to employees.
Kerner is said to have been a 'confidant' of former Volkswagen Group CEO Matthias Mueller, according to Automotive News Europe. It is unclear if the latest arrests and stepped up investigation contributed to Mueller's ouster last week.
Police last year arrested fellow VW Group engineer Wolfgang Hatz, who is still in custody.