Some 85 of the country's 106 NCT vehicle lifts have been found to be in need of repair.
It could be the end of April before the entire network of lifts is fully operational again, the National Car Testing Service (NCTS) has confirmed.
Currently, some 20% of vehicle lifts in NCT centres are functioning, with thousands of motorists facing the prospect of a re-test.
The use of devices at all 47 NCT centres was suspended in late January following concerns over their integrity.
At that time, a full inspection was ordered.
This detailed condition survey of all 106 vehicle lifts has now been completed. Eight were approved to continue testing last week and 13 new lifts have been delivered and replaced defective lifts this week.
The full condition survey identified that some 85 lifts are in need of repair. These devices have a defect on the scissor lift arm which requires a repair.
NCTS has agreed on a repair programme with the lift manufacturer for the remaining 85 vehicle lifts, which are still temporarily suspended.
This repair programme will commence across the network on Monday, March 2 to allow time for the production and delivery of the replacement part. It is anticipated that the repair time for each lift will be approximately two days.
It is expected that 50% of test lanes will be operating by the end of March, with 100% of lifts returned to use by the end of April. A replacement programme for all repaired lifts will then commence in June 2020, according to Grant Henderson, General Manager, NCTS.
"However, we continue to ensure that those who are due a driving test or a taxi NCT roadworthiness test are receiving a full inspection," he said.
NCTS is planning to recruit additional vehicle inspectors and increase operating hours of test centres to accommodate customers in need of a second inspection.
It has advised those customers who are waiting to undergo an underbody re-test only to refrain from booking. NCTS will contact these customers regarding the completion of their test, it said.
Those customers who are due an NCT are advised to continue to book and attend as normal, with the test to be completed with the omission of the underbody inspection. No additional fee will be incurred by the customer for this inspection.
NCTS and the RSA are expected to announce further measures to "minimise customer inconvenience" shortly.
"All vehicle owners are reminded that the roadworthiness of their vehicle is always their responsibility," they added.
Motorists who have completed a partial test are advised to keep their Vehicle Inspection Report with them to present to Gardaí if required.
"Our NCTS staff are working very hard to try and accommodate all customers who are presenting for inspection and where possible they are doing their best to inspect customer’s vehicles in full," Mr Henderson said.