Glitches have hit both of the US space agency's Mars robotic rovers, prompting speculation that they may be suffering the effects of wear and tear.
The rovers have far exceeded their original stay on Mars
A semiconductor component aboard Spirit failed to power up while commands were being executed, preventing scientists from using three of its spectrometers.
But a Nasa official said this was due to a mistiming of two commands.
Spirit's twin, Opportunity, sent error messages back to Earth four times in the past two weeks during operations.
Rover project manager Jim Erickson said the likely solution to Spirit's problem would be to insert a delay between the signals to the component in question, called a gate array.
Spirit has also been suffering from a "sticky" right front wheel, which has been drawing roughly twice the electrical current of the other five.
Ground controllers have mostly been driving it in reverse with five wheels operating, to save its remaining life for situations where it will be needed.
Opportunity's error messages have been occurring during use of the microscopic imager on its robotic arm.
The likely cause is that instrument cabling running along the arm is degrading, officials from Nasa's Jet Propulsion Laboratory (JPL) said.
Both rovers have been experiencing a decline in the amount of power they can obtain through their solar arrays, due to the accumulation of dust on the panels and to the onset of winter on Mars.
The rover missions have been extended twice. Once in April, to provide funding until September, and again in July. Although no new money will be provided, the rovers will continue operations for seven months, starting from October.