Initially used for long-distance express services throughout Luzon, they were relegated to hauling commuter trains within Metro Manila, a task previously done by PNR's diesel multiple units fleet.

This was further exacerbated by the closure of the PNR South Main Line's intercity section in 2012 after an accident in Sariaya, Quezon.

These were ordered in the 1970s to augment and eventually replace the aging diesel locomotive fleet purchased by PNR's predecessor, the Manila Railroad Company.

[9] Despite the earlier diesel locomotives initially having 4 digits, the numbering scheme for the new 900 class has three and seems to follow the numbering scheme of the Manila Railroad 800 class USA locomotives built 30 years prior.

At the same time, the long-distance coaching stock were given a dark green and yellow livery to suit the locomotives.

They entered service in 1992 together with the ten 5000 class locomotives, and had a red paint that will be later incorporated into the Philippines 2000 livery.

[13] In 2014, PNR signed a contract consortium deal with Miescorrail (now MRail), a subsidiary of Meralco and Desco Inc. to upgrade its locomotives.

[2] From 2019, PNR repainted the locomotives to an orange livery in anticipation of the arrival of the new trains from PT INKA.

The U14C Prototypes and U14C are the same with only a few difference which is the batch number, engine block, radiator grills, and date of arrival.

With the closure of the Metro Commuter for 5 years, the serviceable units are currently idle and used for internal movements.

(Since 2024) (since 2024) (Since 2023) (since August 2019) (since 2024) (since 2024) (since 2024) The PNR 900 class locomotives has been involved in various incidents, mostly of derailments, engine malfunctions, collisions, and even attacks by the NPAs (New People's Army) during the 1980s.

[24] Even the locomotives that are declared Beyond Economical Repair (BER) in Caloocan Workshop were repainted in Blue livery except for 5010.

The livery lasted until 2013 when intercity services on the PNR South Main Line were suspended after the derailment of the Bicol Express on October 26, 2012.