The extreme cold temperatures blamed for shutting down rail service in Ottawa's east end last weekend damaged the pantograph on four light rail transit vehicles.

The arm that connects the train to the overhead power lines will be replaced on four vehicles before they re-enter service following the disruption on Saturday.

OC Transpo provided an update on the investigation into the issues with the Confederation Line last weekend.   Five trains came to a stop early Saturday morning in the east end after experiencing a loss of power in the eastern portion of the line.

R1 replacement bus service ran between Hurdman and Blair stations, while reduced O-Train service ran from Hurdman to Tunney's Pasture stations.

In a memo to council Wednesday afternoon, Chief Safety Officer Duane Duquette said the initial investigation found the extended period of cold temperatures affected the catenary power line.

"As part of further analysis completed after repairs were made on the line, it was found that this condition caused damage to the pantograph – the arm that connects the train to the catenary line to provide power – on four light rail vehicles," said Duquette.

Duquette says all necessary repairs and inspections were completed to the track on Saturday, ahead of the return to service on Sunday.

"Pantographs on the four vehicles are being replaced before they reenter service," said Duquette.

The damage to the pantograph requires OC Transpo and Rideau Transit Maintenance to report the incident to the Transportation Safety Board.

"The TSB has been notified. No further follow-up is expected," said Duquette.

"The City and RTM will be further reviewing this incident for any remedial actions or processes that may be required."