The ex-President arrived at Nanterre in the west of Paris on Tuesday alone, and was forced to explain himself to police without his lawyer, already in custody for the same corruption probe.
It's the first time that an ex-President is being investigated, but Sarkozy who was booted out of office in 2012, no longer benefits from legal immunity, which expired last year.
A lawyer by profession, he defended himself against allegations that he used his position to obtain inside information from magistrates about the progress of a probe into the funding of his 2007 election campaign.
The 59 year old is thought to have been tipped off that his mobile phone was being tapped by judges looking into the alleged financing of his campaign by the former Libyan leader Colonel Gaddafi.
Sarkozy is suspected of being helped to victory in 2007 with up to 50 million euros provided by Gaddafi and envelopes stuffed with cash from France's richest woman, L'Oreal heiress Liliane Bettencourt. Allegations he strongly denies.
He could face up to ten years in prison and a fine of 170.000 euros if found guilty. But the case could cost him his political comeback in 2017.
His supporters accuse the government of François Hollande of judicial harrasment, and claim the case is politically motivated. Sarkozy himself has attacked the tapping of his phones as worthy of East Germany's notorious Stasi secret police. He maintains his innocence.