MG Zs 2018: reliability & common MOT faults
Elevated MOT failure patterns for the 2018 MG Zs include Rbt (sp) (~5.4× peers). Based on UK DVSA open data for test year 2025 (1,237 failed first-attempt tests), compared with similar age and mileage peers. Available test years: 2024, 2025.
Common faults
These are MOT failure patterns that show up more often on this registration year than on similar cars of the same class, age band, and mileage in the same test year (leave-one-out peer comparison; whole model family excluded).
Statistical patterns from MOT defect codes — not manufacturer TSBs, recalls, or a diagnosis of any individual car. Fail and advisory patterns are kept separate.
Based on 1,237 failed first-attempt tests in test year 2025.
Rbt (sp)
This failure pattern appears about 5.4× more often than on similar peer cars — recorded on 106 failed first-attempt tests; 8.6% of failed tests for this model year.
Any · 106 failures · ×5.4 vs similar cars · 8.6% of failed first tests · Strong pattern — appears far more often than similar cars
| # | Fault pattern | Location | Failures | vs similar cars | Share of fails | Confidence |
|---|---|---|---|---|---|---|
| 1 |
Wheel bearings (front)
Suspension > Wheel bearings
|
Front | 78 | ×19.9 | 6.3% | Likely common fault pattern |
| 2 |
Anti-lock braking system
Brakes > ABS / EBS / ESC > Anti-lock braking system
|
Any | 93 | ×14.5 | 7.5% | Likely common fault pattern |
| 3 |
Electronic stability control
Brakes > ABS / EBS / ESC > Electronic stability control
|
Any | 70 | ×12.4 | 5.7% | Likely common fault pattern |
| 4 |
Parking brake control — Lever
Brakes > Parking brake control > Lever
|
Any | 34 | ×5.8 | 2.7% | Likely common fault pattern |
| 5 |
Rbt (sp)
Brakes > Brake performance > Parking brake efficiency (sp) > Rbt (sp)
|
Any | 106 | ×5.4 | 8.6% | Strong pattern — appears far more often than similar cars |
| 6 |
Service brake performance (rear)
Brakes > Brake performance > Service brake performance > Rbt > Service brake performance
|
Rear | 50 | ×3.7 | 4.0% | Likely common fault pattern |
| 7 |
Headlamp
Lamps, reflectors and electrical equipment > Headlamps > Headlamp
|
Any | 111 | ×3.6 | 9.0% | Likely common fault pattern |
| 8 |
Coil spring (rear)
Suspension > Springs > Coil springs > Coil spring
|
Rear | 111 | ×2.8 | 9.0% | Possible elevated fault |
| 9 |
Headlamp (front)
Lamps, reflectors and electrical equipment > Headlamps > Headlamp
|
Front | 88 | ×2.8 | 7.1% | Possible elevated fault |
| 10 |
Malfunction indicator lamp
Noise, emissions and leaks > Exhaust emissions > Spark ignition > Malfunction indicator lamp
|
Any | 70 | ×2.0 | 5.7% | Possible elevated fault |
Only patterns that clear minimum sample and elevation thresholds are shown (at least 20 failures and 2.0× peer lift).
Wear patterns
These patterns look like wear or usage effects rather than model-specific design faults. Tyres, brake friction material, and alignment-related defects often track mileage and road use. They are not treated as a model design fault in our common-faults ranking.
| # | Pattern | Location | Failures | vs similar cars | Share of fails | Confidence |
|---|---|---|---|---|---|---|
| 1 |
Brake discs (rear)
Brakes > Mechanical brake components > Brake discs and drums > Brake discs
|
Rear | 92 | ×5.5 | 7.4% | Wear / usage pattern — not treated as a model design fault |
| 2 |
Tyre pressure monitoring system
Tyres > Tyre pressure monitoring system
|
Any | 62 | ×2.0 | 5.0% | Wear / usage pattern — not treated as a model design fault |
Advisories
Advisory items recorded on failed first-attempt tests that appear elevated versus peers. Advisories are not a fail rate — they flag issues noted at the test, often before they become failures.
| # | Advisory pattern | Location | Notes | vs similar cars | Share | Confidence |
|---|---|---|---|---|---|---|
| 1 |
Suspension arm (front)
Suspension > Suspension arms > Suspension arm
|
Front | 62 | ×42.8 | 5.0% | Elevated vs peers |
| 2 |
Sub-frame (front)
Suspension > Sub-frames > Sub-frame
|
Front | 88 | ×40.1 | 7.1% | Elevated vs peers |
| 3 |
Wheel bearings (front)
Suspension > Wheel bearings
|
Front | 42 | ×18.5 | 3.4% | Likely common fault pattern |
| 4 |
Service brake performance (rear)
Brakes > Brake performance > Service brake performance > Rbt > Service brake performance
|
Rear | 60 | ×4.5 | 4.9% | Likely common fault pattern |
| 5 |
Brake discs (rear)
Brakes > Mechanical brake components > Brake discs and drums > Brake discs
|
Rear | 276 | ×3.0 | 22.3% | Wear / usage pattern — not treated as a model design fault |
| 6 |
Engine oil leaks
Noise, emissions and leaks > Fluid leaks > Engine oil leaks
|
Any | 48 | ×2.1 | 3.9% | Elevated vs peers |
FAQs
About this data
Universe. UK class 4 cars only; normal MOT tests (not retests); results pass, PRS, or fail; one first test per vehicle per calendar year.
PRS policy. PRS means the vehicle failed items that were fixed at the test station and then passed the same day. We count PRS as a first-attempt fail in headline rates so same-day repairs do not hide problems.
Peer baseline. We compare this model year with other class 4 cars of similar age and mileage in the same test year, excluding the whole model family so the car is not compared with itself (leave-one-out peer baseline).
Data years. Test years covered: 2024, 2025.
Limitations.
- MOT tests do not cover engine internals, gearboxes, or many electronic modules — so this is not a full reliability score.
- Common faults are inferred from MOT defect statistics, not manufacturer TSBs or recalls.
- Matching on age and mileage reduces but does not remove every usage or maintenance difference between cars.
- Pass rates and star scores appear only when those data marts are available; this page never invents them.
Display rules config: 1
Contains public sector information licensed under the Open Government Licence v3.0.