Malaysia's state oil firm said the refinery had started feeding crude oil into the unit earlier this week, confirming an earlier Reuters report citing sources.
"We confirm that the refinery has started feeding crude to its CDU earlier this week in efforts to restart the plant," Petronas told Reuters over email.
The Pengerang Refining development, part of Petronas' $27 billion (£22 billion) Pengerang Integrated Complex, consists of a 300,000 barrels-per-day (bpd) oil refinery and a petrochemical complex with a production capacity of 7.7 million tonnes per year in the southern Malaysian state of Johor.
The project, originally known as RAPID, or Refinery and Petrochemical Integrated Development, was shut in April after a fire damaged its atmospheric residue desulphurisation (ARDS) unit.
It had been scheduled to restart last month but that was pushed back to August, they said.
Repairs at the ARDS unit were expected to take months so the refinery has modified the type of crude it processes to low-sulphur oil such as Murban crude from Abu Dhabi, the sources said.
Petronas said the ARDS is scheduled to come back online in 2020.
The refinery's strong demand for Murban crude saw Malaysia's imports of the oil jump to about 4.6 million barrels in June and July, Refinitiv data showed.
(Reporting by Florence Tan & Joseph Sipalan; editing by Simon Cameron-Moore)
By Florence Tan