| Fail category | Share of tests | What it usually means |
|---|---|---|
| Steering and suspension | 18.5% | Worn joints, bushes, track rod ends and play in the steering, found in the visual inspection. |
| Lighting and electrical | 17.6% | Blown bulbs, cracked lenses, faulty indicators, warning lights on the dashboard and horn. |
| Side slip (wheel alignment) test | 15.2% | Wheels pulling out of line when the car drives over the side slip plate: usually alignment or worn parts. |
| Wheels and tyres | 12.8% | Tread below the legal limit, damage, mismatched tyres or wrong sizes. |
| Brake performance test | 11.7% | Brakes that are weak, uneven left to right, or a handbrake that does not hold on the roller tester. |
| Braking equipment | 9.3% | Visual faults in pipes, hoses, discs and pads. |
| Headlight aim test | 9.3% | Headlights pointing too high, too low or to the side. |
| Vehicle and safety equipment | 8% | Seat belts, wipers and washers, mirrors, windscreen damage and similar items. |
| Suspension (shock absorber) test | 6.1% | Shock absorbers that do not control the wheel on the test rig. |
| Chassis and body | 5.7% | Corrosion, sharp edges and structural damage. |
| Engine, noise and exhaust | 5.4% | Leaks, loud or damaged exhausts and engine issues. |
| Emissions | 5.1% | Exhaust gases or smoke above the limit for the car. |
Share of 2025 initial tests with at least one defect in the category. One car can fail on several categories, so the percentages add up to more than the fail rate.
Reading your NCT report
Every defect on the Vehicle Inspection Report is classed as minor, major or dangerous. The NCTS publishes an explained sample report. What each result means and what to do next is in the result explained and the retest.
OBD, tow bars and headlights
- OBD: the inspector plugs a scanner into the car's diagnostic port (usually under the steering wheel, sometimes in the glove box). It checks the VIN, reads the odometer and records brake system (ABS/EBS) error codes. Codes give an Advisory Pass for now.
- Tow bars: the trailer socket output is tested and the tow ball is measured for wear.
- Headlamp aim: make sure the lens is clean, there is no condensation, a recently changed bulb sits correctly, and tyre pressures are right, as they affect the aim.
Source: NCTS FAQ (questions 11, 12, 24 and 25) and the NCT Manual.
Frequently asked questions
Will an OBD fault code fail the NCT?
OBD testing is being introduced in phases. Initially, an error code gives an "Advisory Pass": it is recorded on the report and you are advised to fix it, but the car does not need to come back for that item alone.
Does the NCT check tow bars?
Yes. The output of any fitted trailer socket is checked and the tow ball or pin is measured for wear.
How common is a headlamp aim fail?
Headlamp aim is one of the most common reasons for failure: in 2024, 140,602 vehicles (5.03%) failed on it. Getting the lights checked and set before the test is the simplest fix.
What is the most common reason for failing the NCT?
In 2025 the most frequent fail category was steering and suspension, recorded in 18.5% of initial tests, followed by lighting and electrical (17.6%).
Can I fix a fail and avoid a full retest?
Yes. Book the retest within 21 days and complete it within 30 days. If only visual items failed, the retest is free; otherwise it costs €40.
Related guides
Pre-NCT checklist
Check these before you go.
NCT retest
Rules and cost.
By car model
What your car fails on.
Sources: RSA 2025 Make and Model Data · NCTS FAQ. NCT Centres is independent and not affiliated with the NCTS or the RSA. Fees and rules can change: confirm on ncts.ie before you book.