"Whether our party president is guilty or not is not the issue today. The issue is that all of us in public life should be beyond reproach," he told PTI.
Sinha's demand brings alive once again the campaign initiated by BJP Rajya Sabha MP Ram Jethmalani and his son Mahesh for the party chief's resignation in the wake of reports of alleged dubious financing of Purti Sugar and Power Group.
The campaign against Gadkari had appeared to take a backseat after the party backed him in the wake of a clear chit given by auditor S Gurumurthy, who had gone into the balance sheet and accounts of the Purti group.
But its revival may have come at an inappropriate time when the party plans to corner the government on various issues, including alleged scams, in the winter session of Parliament beginning Thursday.
Sinha said he was issuing his statement for Gadkari's resignation with a "great deal of sadness and regret and after exhausting the forums available" for him in the party.
"I am confident that the issue I am raising has merit and I have faith in the wisdom of the party to be able to deal with this issue.
"In fact, it is this faith which kept me from issuing this statement earlier. Unfortunately, despite my best effort the party has been unable to take a decision in the matter," he said.
Recalling that in the past too he had raised his voice against supporting Anshuman Mishra in the Rajya Sabha elections, Sinha said, "the party had heeded my advice then as I hope it does now.
"The BJP has always set the highest standard of conduct in the past which should be followed even now now. We were a party with a difference earlier. We must continue to be a party with a difference even today and in future."
The former Union Minister said he has been "greatly saddened" by the events over the last few weeks.
"We have also deeply disappointed those who were looking towards us to fight the mind boggling corruption of the Congress party.
"We have no right to let down the people of India this is what we have done by taking the easy way out through a questionable method of self certification," he said taking a dig at Gurumurthy's clean chit.