NASA has to make a last attempt to connect with Mars's Maritime Opportunity Marine before pulling out the mission in 15 years.
The possibility was silent eight months after a huge dust storm on the planet.
Thick dust darkened the Martian sky in June last year, interrupting the power of the router with solar power.
A quarter of the planet was swallowed by the storm that was even found on the other side of Mars by the nuclear engine Curiosity.
NASA announced that it had sent the last set of recovery commands on Tuesday, responding by mid-Wednesday.
In the absence of a response, as the agency expects, NASA will announce the queue dead.
An opportunity launched in 2003 and landed in 2004. Since then, it has covered more than 45km (28 miles).
It was expected to be active in just over 90 days in the Earth's time, but it has exceeded that goal by more than 14 years.
The Double Rover Opportunity, Spirit, was declared dead in 2011 after falling into sand in 2009.
NASA project manager John Callas told the AP: "It's like a loved guy who's gone, and you still hope that they will appear and that they're healthy.
"But every passing day is diminishing and at one point you have to say" enough "and go on with your life.
Deputy scientist Abigail Freyman, a 16-year high school student when Opportunity lands on Mars, adds: "This gives you an idea of how long this mission has continued.
"The possibility is just a work basket … I think it really is a testimony of how well the mission is designed and how careful the vehicle management team is.
NASA engineers believe that Opportunity's internal clock may have been shuffled during a break caused by the dust storm.
If this happens, the sleeping cycle of the river – which is meant to save energy during darkness – can be damaged, exhausting the batteries.
The possibility "gave us a bigger world," said Dr. Kallas, adding: "Mars is already part of our neighborhood."