"Opportunity likely experienced a low-power fault, a mission clock fault and an up-loss timer fault. The team is continuing to listen for the rover over a broad range of times, frequencies and polarizations using the Deep Space Network (DSN) Radio Science Receiver. The team has begun mission clock fault recovery commanding 'in the blind,' in the hopes of catching the rover during an awake period, as their strategy of last resort."

Source: NASA mission update for sols 5340-5346 (Jan. 31-Feb. 6, 2019) https://mars.nasa.gov/mer/mission/rover-status/opportunity/r...