These second-generation trains first entered service in 1995 on the North-South Line (NSL) and East-West Line (EWL). 19 such trainsets were manufactured from 1993 to 1994 by Siemens AG in Vienna, Austria, with a design lifespan of 30 years.
Mid-life upgrading works were slated for the C651 trains, and was first carried out on Train Sets 217/218 and 227/228 between 2015 and 2018. However, leading up the transition to the New Rail Financing Framework (NRFF) in August 2016, the LTA would eventually make decisions on building-up, replacement and upgrading of assets. Coupled with changes in SMRT Corporation’s management structure, the mid-life upgrading of C651 trains was abruptly discontinued, and planned refurbishments to the C151 were thus precluded.
While LTA announced its intention to replace the first-generation C151 trains with brand-new ones in September 2016, no further announcements were made with regards to the replacement of the second-generation C651 trains. In September 2020, R151 trains manufactured by Bombardier were confirmed as the replacement for these trains.
Train car 3230 (from Set 230) was announced to be preserved by the Singapore Police Force for training purposes in August 2021. On 28 August 2021, train cars 3229 & 1229 (from Set 229) was observed to be transported elsewhere, while car 2229 (from Set 229) was sent to the scrapyard.