The YJ design is based on pre-war PL2 class 2-6-2, itself derived from the JF6 2-8-2, the predecessor of the well known SY class mikado. According to Chinese sources a total of 202 locos were produced between 1958 and 1961. Jinan built 117, Tangshan 80, Wuchang 2 and Mudanjiang 3.

Locos observed fall into two distinct number ranges, YJ 104 - 179 & YJ 201 - 317. From the builders details reported, it appears that Tangshan built the lower numbered locos while Jinan produced those numbered above 200. There have been no reports of locos with Mudanjiang plates and only one instance of a Wuchang built loco. YJ 403 has been reported dumped at Fuxin and could possibly be one of a small batch built at one of these works. Alternatively, it could just be a local renumbering of a Tangshan or Jinan built loco. The only positive sighting of a Wuchang built loco is one of the large Wuhan Steelworks fleet, last reported in 1987. Unfortunately all these locos are renumbered in a local series so the original number is unknown.

Unusually for a standard loco, there are three variations in cylinder dimensions. The first 50 Jinan locos have small cylinders with the same principal dimensions as those fitted to the 1908, ALCo built, DB1 2-6-4 tanks. Before anyone starts speculating, that's where the similarity ends. Later Jinan locos have the same cylinder dimensions as the PL2 2-6-2s while Tangshan's engines were built with the larger cylinders with similar dimensions to those fitted to the JF6 and SY mikados.

As mentioned on the PL2 page, it is possible that some locos identified as PL2 are actually YJ class in disguise. In most respects, the two classes are virtually identical. The variation between the cylinder dimensions of different batches of YJ appear more significant than the differences between YJ and PL2 classes. Most YJ are fitted with a conventional tender but a few have been seen with slope backed tenders similar to those usually found on PL2 class engines.

The last report of a YJ in normal service was Baotou Steelworks' YJ 232 in early 2002. Then, just as it looked unlikely that a YJ would ever work again, Tiefa acquired the long dumped YJ 269 from Xuanhua steelworks and returned it to service, ostensibly for special trains but it seems to have become a bit of a favourite for working regular passenger trains on the Tiefa network.