Reading 903 was one of the first six FP7s ordered by the railroad in March 1950 to replace passenger steam locomotives. It and sister Reading 902 were completed on June the 1st of that year and delivered to the Reading via the Baltimore and Ohio Railroad. The pair pulled their first train on June 6. In the following years, the two locomotives sometimes worked together, and sometimes were split, depending on the size of their trains.
SEPTA inherited the units in 1974, and they were renumbered by the new Consolidated Rail Corporation in 1976, the 903 becoming 4373. It was the first FP7 to receive SEPTA paint in February 1978. During the SEPTA years, the FP7s usually operated in push-pull. SEPTA ceased all diesel-operations in 1981, and the locomotives were retired.
Locomotive 903 was purchased by the Philadelphia Chapter of the National Railway Historical Society (NRHS) in September 1983 and was stored at the Railroad Museum of Pennsylvania along with its sister, the 902, which was owned by the Lancaster Chapter of the NRHS. Restoration on the two began in 1986 and was completed in 1995.
Locomotives 903 and 902 (now owned by the Reading Technical and Historical Society) operated an excursion on an ex-Reading line owned by Penn Eastern Rail Lines in October of that year, but no more trips are planned for 2008.
In January 2010, the 902 and 903 were loaned to Steamtown National Historic Site for a year to maintain the locomotives in exchange for excursion rights. As of 2014, both units are still located at the park, but are out of service and on display.