Oil contamination was discovered in the hydraulic system for the deck, meaning a part will not have to be replaced.
This has been ordered, but will not arrive by the time the vessel sets sail on its first in-service voyage.
CalMac has confirmed that the Glen Sannox will finally begin work on 13 January with regular sailings from Troon to Brodick on Arran.
The ferry is more than six years overdue, and millions of pounds over budget.
The Caledonian MacBrayne ferry MV Glen Sannox will enter service on Monday (Image: Jane Barlow) Since being handed over in mid-November, her crew have been carrying out familiarisation activities including sea trials.
The ferry operator said that a “small number” of issues will continue to be addressed during the first few stages of service, as was the case with both of CalMac’s last two major vessels to enter service – MV Finlaggan and MV Loch Seaforth.
The cleanliness of the oil in the hydraulic system was checked and found to be satisfactory, meaning the system filter have been effective in capturing the containments.
All other hydraulic components onboard the vessel were tested and found to be fully functional.
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Given demand levels now and in the coming months, this does not affect planned service levels or capacity.
Duncan Mackison, CalMac’s Chief Executive Officer, said: “Great effort has gone into getting MV Glen Sannox ready for service for Monday.
“It is testament to the commitment of people at CalMac to Arran that we’ve been able to reduce our original schedule for familiarisation and meet an ambitious target for entry to service.
“Launching a new major vessel is akin to buying a new build house. You can move into a new home whilst some small snags are fixed, and we can operate MV Glen Sannox whilst we address a small number of minor issues that have no bearing on the safe operation of the vessel, or the experience passengers have on board.”
He added: “We are excited to welcome people on board and look forward to seeing a vessel which will bring great benefit to Arran enter service for the local community.”