Tram-train services between Sheffield and Rotherham, which have been plagued by problems, were suspended after a fault was detected on one of the vehicles.
Operator Supertram said an issue was identified on one of its Citylink vehicles on Tuesday night and further tests were needed to see if others in the fleet were affected.
The manufacturer detected a potential problem relating to the structure underneath the vehicle, known as the bogie.
Stagecoach said the issue related to a bracket on the bogie which was not linked to the mechanical running of the vehicle but added it must be rectified found before trams can re-enter service.
Services resumed on Wednesday afternoon - with services running every 30 minutes between Sheffield Cathedral and Parkgate.
The scheme has been plagued by problems since it was first mooted.
It was due to launch in 2015 at a cost of around £15 million but it launched last year, with a bill of around £75 million.
It was then involved in a crash on its first day of service at the junction of Staniforth Road and Woodbourn Road.
And in November, one of its vehicles was also in collision with a car at the same junction.
A spokesman for Supertram said: “We are sorry for the disruption this has caused to our customers.
"For safety reasons, the vehicle manufacturer has identified the need to carry out checks, and possibly additional work, on our Citylink vehicles following a fault that was detected on one tram train yesterday.
"This is having a significant impact on our tram-train services in particular.
“I would like to reassure passengers that these checks will be done as quickly as possible to minimise the level of disruption.
"We would like to thank customers for their patience while we do this work and apologise again for the impact this is having on their journeys.”