Model Reports 8 min read Updated 11 Sep 2026 DVSA open data · 4,845 tests analysed

MG Zs 2018: reliability & common MOT faults

1,237 first-attempt MOT failures were recorded on the 2018 MG Zs in 2025. The items recorded most often on them were Headlamp and Coil spring (rear). Figures are among first-attempt failed MOT tests, not among all tests.

2018 Zs break the Zs's own run — at 74.5% they land 3.8 pp above the midpoint of the 2017 and 2019 cars either side.

First-attempt pass

74.5%

of 4,845 first tests (2025)

First tests

4,845

test year 2025

Failed first attempts

1,237

failed first-attempt tests

Most common fail

9.0%

Headlamp

MOT pass rates

First-attempt and official-style rates among class 4 first tests of the year.

First-attempt pass

74.5%

of 4,845 first tests (2025)

Official-style pass

78.8%

incl. same-day PRS fixes

First tests

4,845

class 4 · first MOT of the year

Typical age 7.0 yrs · median mileage 45,782 mi

vs 2024: -1.1 pp first-attempt

Note:

  • Class 4 cars · first MOT of the year per vehicle · P/PRS/F outcomes (2025 data).
  • PRS (fixed at the station the same day) counts as a fail in the first-attempt rate.
  • Raw outcomes for this cohort — not adjusted for age, mileage, or peer mix.
  • MOT doesn't test engine or gearbox internals.

Common faults

Failure patterns that show up more often on this registration year than on similar cars.

These MOT failure patterns show up more often on this registration year than on similar cars of the same class, age, and mileage.

Shares below are measured across the 1,237 failed first attempts in 2025 that the age-and-mileage comparison can be computed on.

Standout: Rbt (sp) — 8.6% of this year's failed first attempts

Recorded on 106 of those tests. It tops the table on elevation — about 5.4× more often than on similar cars of the same age and mileage. That is what makes it unusual for its class, which is a different question from what is most likely to fail; the buying checklist ranks by that. The full ranked list is in the table below.

Fault pattern Location Failures vs similar cars Share of fails Confidence
Wheel bearings (front)
Suspension > Wheel bearings
 Front 78 ×20 6.3% Likely
Anti-lock braking system
Brakes > ABS / EBS / ESC > Anti-lock braking system
 Any 93 ×14 7.5% Likely
Electronic stability control
Brakes > ABS / EBS / ESC > Electronic stability control
 Any 70 ×12 5.7% Likely
Parking brake control — Lever
Brakes > Parking brake control > Lever
 Any 34 ×5.8 2.7% Likely
Rbt (sp)
Brakes > Brake performance > Parking brake efficiency (sp) > Rbt (sp)
 Any 106 ×5.4 8.6% Strong
Service brake performance (rear)
Brakes > Brake performance > Service brake performance > Rbt > Service brake performance
 Rear 50 ×3.7 4.0% Likely
Headlamp (front)
Lamps, reflectors and electrical equipment > Headlamps > Headlamp
 Front 111 ×3.6 9.0% Likely
Coil spring (rear)
Suspension > Springs > Coil springs > Coil spring
 Rear 111 ×2.8 9.0% Possible
Malfunction indicator lamp
Noise, emissions and leaks > Exhaust emissions > Spark ignition > Malfunction indicator lamp
 Any 70 ×2.0 5.7% Possible

Only patterns that clear minimum sample and elevation thresholds are shown (at least 20 failures and about 2.0× more often than similar cars).

Note: Rates and comparisons are among first-attempt failed tests, not all MOTs. Patterns come from MOT defect codes — not manufacturer service bulletins, recalls, or a diagnosis of any individual car. Failures and advisories are listed separately.

Wear patterns

Usage and mileage effects that often track road use rather than model design.

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.

Pattern Location Failures vs similar cars Share of fails Confidence
Brake discs (rear)
Brakes > Mechanical brake components > Brake discs and drums > Brake discs
 Rear 92 ×5.5 7.4% Wear
Tyre pressure monitoring system
Tyres > Tyre pressure monitoring system
 Any 62 ×2.0 5.0% Wear
Note: These patterns are not treated as a model design fault in our common-faults ranking.

Advisories

Notes recorded at the test that appear more often than on similar cars.

Advisory notes recorded on failed first-attempt tests that appear more often than on similar cars.

Advisory pattern Location Notes vs similar cars Share Confidence
Suspension arm (front)
Suspension > Suspension arms > Suspension arm
 Front 62 ×43 5.0% Elevated
Sub-frame (front)
Suspension > Sub-frames > Sub-frame
 Front 88 ×40 7.1% Elevated
Wheel bearings (front)
Suspension > Wheel bearings
 Front 42 ×18 3.4% Likely
Service brake performance (rear)
Brakes > Brake performance > Service brake performance > Rbt > Service brake performance
 Rear 60 ×4.5 4.9% Likely
Brake discs (rear)
Brakes > Mechanical brake components > Brake discs and drums > Brake discs
 Rear 276 ×3.0 22.3% Wear
Engine oil leaks
Noise, emissions and leaks > Fluid leaks > Engine oil leaks
 Any 48 ×2.1 3.9% Elevated
Note: Advisories are not a fail rate — they flag issues noted at the test, often before they become failures.

If you are buying one

What this year's MOT record means for the decision in front of you.

This year outperforms the Zs's own age curve — it holds up better than its place in the model's run would predict.

Other Zs years worth knowing about

Newer cars always pass more often, so a plain "best year" list would just rank by age. These are the years that beat or miss the trend their own neighbouring years set — the only age-adjusted signal this data supports.

Year vs the years either side First-attempt pass (rises with newer cars) First tests
2021 Zs +3.4 pp better 86.5% 14,459
2017 Zs -8.4 pp worse 66.1% 333
2019 Zs -2.5 pp worse 75.3% 8,181
2022 Zs -1.7 pp worse 85.2% 17,287

What to check on a 2018 Zs

The items that failed 2018 Zs most often, as a share of the year's failed first attempts. This is what goes wrong, not what is unusual — the table further up the page covers that.

  • Headlamp — recorded on 9.0% of failed first attempts
  • Coil spring (rear) — recorded on 9.0% of failed first attempts
  • Tyres — Condition (front) — recorded on 8.8% of failed first attempts
  • Rbt (sp) — recorded on 8.6% of failed first attempts
  • Tread depth (front) — recorded on 7.9% of failed first attempts

Every figure here is a first-attempt MOT rate from DVSA open data for this model line. MOTs do not test engine or gearbox internals, so this is a pre-purchase checklist, not a full reliability score.

FAQs

Short answers about how to read this model-year guide.

2018 Zs break the Zs's own run — at 74.5% they land 3.8 pp above the midpoint of the 2017 and 2019 cars either side. In 2025, 74.5% of 4,845 first MOTs on the 2018 MG Zs passed first time (PRS — items fixed at the station the same day — counted as a fail). The official-style rate including PRS is 78.8%. Among 1,237 failed first-attempt MOT tests (test year 2025), Rbt (sp) appears more often than on similar cars (8.6…
Ranked by how often they were actually recorded, the items that failed 2018 MG Zss most often at the first attempt were Headlamp (9.0%), Coil spring (rear) (9.0%) and Tyres — Condition (front) (8.8%) — each as a share of the year's failed first attempts. That is what goes wrong on the car. It is a different question from which patterns are unusual for the class, which the common-faults table answers.
Among failed first-attempt tests we highlight patterns that appear more often than on similar cars. Top example: Rbt (sp) (8.6% of those tests; 106 observed failures; about 5.4× more often than similar cars). These are statistical signals, not a diagnosis of any individual car.
Rbt (sp) shows up more often than on similar cars (8.6% of those tests; 106 observed failures; about 5.4× more often than similar cars). That does not prove a design fault — age, mileage, and how the car was used still matter. Treat it as a pre-purchase check point, not a manufacturer service bulletin.
Common MOT problem areas for the 2018 MG Zs include Rbt (sp), Wheel bearings (front), Anti-lock braking system. These patterns show up more often than on similar cars after we filter out sparse noise — not a full list of every possible fault on an individual car.
Advisories flag issues noted at the test and are not a fail rate. We show advisory patterns that appear more often than on similar cars among failed first-attempt tests, separate from common failure rows. Use them as early-warning checks, not as a pass/fail score.
This page highlights MOT failure patterns for the 2018 MG Zs (registration year) using UK DVSA open data for the selected test year. Patterns are compared with cars of a similar age and mileage. It is a buyer checklist from MOT defect statistics — not a full service history or manufacturer service-bulletin list.
No. MOT tests do not cover engine internals, gearboxes, or many electronic modules. Patterns here come from MOT defect statistics only and should not be read as engine or gearbox reliability scores.

About this data

How this page is built and what it can (and can't) say.

These figures come from UK MOT open data for this model year. We surface common failure patterns against similar cars — not a full reliability score, and not a pass/fail verdict on any individual vehicle.

2024 2025

What we include

UK Class 4 cars only. Normal MOT tests (not retests); first test per vehicle per calendar year; results pass, PRS, or fail.

Same-day repairs

PRS means the car 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.

How we compare

We compare this model year with other Class 4 cars of similar age and mileage in the same test year. This model family is left out of the peer group so the car is not measured against itself.

What this does not cover

  • MOTs do not cover engine internals, gearboxes, or many electronics — this is not a full reliability score.
  • Common faults come from MOT defect stats, not manufacturer TSBs or recalls.
  • Age and mileage matching reduces — but does not remove — differences in how cars were used and maintained.
  • We never invent pass rates, star scores, or ranks when those data marts are missing.

Contains public sector information licensed under the Open Government Licence v3.0.

Check any vehicle’s MOT history

Full MOT history, mileage records, and reliability insights for any UK vehicle.

Run a free check