Williams admitted its frustration as it was unable to carry out its scheduled programme on the final day of the opening test in Spain.
Felipe Massa was able to complete only 54 laps in the FW38, with the bulk of those coming in the morning, when the Brazilian completed constant speed aero runs.
Massa ultimately ended the day in ninth place, with a time of 1:26.942.
"Today was one of those days I’m afraid" said Williams' Chief Test and Support Engineer Rod Nelson.
"We spent most of the morning doing aerodynamic correlation work which was pretty successful. We are getting through our programme day by day.
"Sadly, we had an issue with one of the car systems over lunchtime and that curtailed a lot of our running this afternoon which we had planned.
"We know what the issue is, we’ve got a solution, and now we look forward to next week."