The space agency said Wednesday the voltage change was first discovered on Sunday and engineers think it might be some kind of short.
The six-wheel, nuclear-powered rover halted work as a precaution.
So far, there's no sign that the problem is related to a computer reboot earlier this month that put Curiosity in safe mode.
Curiosity landed in a Martian crater in August 2012 and has spent the last several months driving toward its ultimate destination, Mount Sharp.
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