Online accounts say there's a radiation source for heating during the lunar night, but it seems one of the solar panels used for normal operations didn't fold up properly (by folding up these panels are closer to the heat source) before the sun went down, and that exposed component froze and was ruined, which sealed the spacecraft's fate.

Source: http://www.dvice.com/2014-2-12/chinas-jade-rabbit-lunar-rove...