It said on Monday the power plant started its pre-commissioning activities in August 2013 and began commissioning activities for Block No. 1 in November 2013.
Kimanis Power said the plant had been providing "test power" to the local electricity grid since Jan 13.
The plant also provided support to the local grid during the Jan 17 blackout in Sabah.
Block No. 2 was commissioned recently, it added.
"Commercial operations of the three generating blocks will be achieved after completion of mandatory testing requirements which are expected to be completed in the second quarter for generating Block No. 1 and the third quarter for generating Blocks No. 2 and 3," it said.
The actual commercial operation date for the project would depend on the completion of the transmission lines.
Kimanis Power is a 60:40 joint venture between Petronas Gas Bhd and NRG Consortium (Sabah) Sdn Bhd, a business arm of Yayasan Sabah.
The company was responding to news reports that the deadline to complete the power plant could be delayed further.