KiwiRail said at 1pm on Monday the Kaiārahi noted a temperature fault related to a lubrication pump on the Wellington to Picton sailing.
A passenger on the ferry said a call came over the loudspeaker that the technical issue would not be fixed quickly and the vessel would have to return to port in Wellington.
But KiwiRail said the ferry had remained in Wellington Harbour as a precaution while engineers investigated the issue.
"The fault was quickly resolved and the vessel is now on its way to Picton, around an hour behind schedule," the statement from a spokesperson said.