New Orange and Red Line trains returned to passenger service on Monday, the MBTA announced.
The trains were pulled from service on June 20 after a new Orange Line car experienced battery failure at the Wellington Yard. The train was out-of-service at the time but the MBTA removed all new Orange and Red Line cars from service while engineers and technicians worked to identify the issue's cause, noting safety is the agency's "top priority."
According to the transportation agency, the battery that failed "provides low-voltage DC power, controlling the electrical equipment on the vehicle and powering lighting, signage, and communications equipment."
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The train manufacturer, CRRC, and the MBTA worked together to identify the cause of the problem as an out-of-range battery temperature reading, which caused the battery to "overcharge for an extended duration and fail."
A design change was made that increases airflow in the battery compartment, the agency said. Additionally, a modification to the temperature sensing circuitry "was developed, implemented, and successfully tested over the weekend."
The new cars returned to service Monday afternoon, the MBTA said, adding that it is grateful to T riders for their patience while engineers worked to ensure the cars are safely and reliably performing.
