The satellite has been placed in a semi-dormant state that conserves energy as the space agency works to investigate and assess the problem.
"The investigation is ongoing, but expectations of a full recovery are low," the agency said.
Government and commercial users of the satellite have been told that no new orders for imagery from Radarsat-I are being taken.
MDA, which is the worldwide distributor of Radarsat-1 data, said the problem was not significant to its business.
Radarsat-1 was launched in 1995 and at the time was expected to operate for 12 years.
Radarsat-2 was launched in 2007.