The review followed questions from the Herald arising from the mayor's affair, including whether he breached the council's code of conduct.
Three days after Mr Brown won a second term, the right-wing Whale Oil blog revealed intimate details of his affair with Ms Chuang, a member of the council's Ethnic Peoples Advisory Panel.
Mr Brown vowed to stay on as mayor as revelations swung from his use of hotel rooms to claims that the election team of his right-wing mayoral rival John Palino had been plotting to expose the affair.
Mr Palino's campaign manager, Luigi Wewege, left the country after emails were published by the Herald showing he had been in an intimate relationship with Ms Chuang and wanted her to reveal the Brown affair.
The Ernst & Young report, commissioned by council chief executive Doug McKay and meant to be reported back as "quickly as possible", is three weeks past its deadline.
The council code of conduct says members have a duty to act honestly, with integrity and uphold the law on all occasions.
It says a conflict of interest may arise from a "personal relationship".
What's involved
Any use of council resources within the office of the mayor, in respect of the mayor's relationship with Bevan Chuang, that contravenes council policies.
Any improper preferential treatment in relation to Ms Chuang's engagement as an employee, contractor or an adviser within the Auckland Council group.
Any other issues that the reviewers or chief executive consider relate to, or arise out of, the above matters.