Model Reports 8 min read Updated 11 Sep 2026 DVSA open data · 11,763 tests analysed

MG Zs 2020: reliability & common MOT faults

2,233 first-attempt MOT failures were recorded on the 2020 MG Zs in 2025. The items recorded most often on them were Tyres — Condition (front) and Tread depth (front). Figures are among first-attempt failed MOT tests, not among all tests.

Electric Zs passed first time 3.7 pp more often than petrol ones (83.1% of 5,182 vs 79.4% of 6,581).

First-attempt pass

81.0%

of 11,763 first tests (2025)

First tests

11,763

test year 2025

Failed first attempts

2,233

failed first-attempt tests

Most common fail

14.5%

Tyres — Condition (front)

MOT pass rates

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

First-attempt pass

81.0%

of 11,763 first tests (2025)

Official-style pass

84.7%

incl. same-day PRS fixes

First tests

11,763

class 4 · first MOT of the year

Typical age 5.0 yrs · median mileage 34,098 mi

vs 2024: -3.1 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 2,232 of 2,233 failed first attempts that recorded an odometer reading in 2025 — the subset the age-and-mileage comparison can be computed on.

Standout: Catalyst emissions — 5.6% of this year's failed first attempts

Recorded on 124 of those tests. It tops the table on elevation — about 7.7× 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 58 ×14 2.6% Likely
Catalyst emissions
Noise, emissions and leaks > Exhaust emissions > Spark ignition > Catalyst emissions
 Any 124 ×7.7 5.6% Strong
Headlamp (front)
Lamps, reflectors and electrical equipment > Headlamps > Headlamp
 Front 217 ×6.1 9.7% Strong
Rbt (sp)
Brakes > Brake performance > Parking brake efficiency (sp) > Rbt (sp)
 Any 99 ×4.3 4.4% Likely
Service brake performance (rear)
Brakes > Brake performance > Service brake performance > Rbt > Service brake performance
 Rear 78 ×3.9 3.5% Likely

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
Headlamp aim not tested (front)
Lamps, reflectors and electrical equipment > Headlamp aim > Headlamp aim not tested
 Front 41 ×7.2 1.8% Wear
Brake discs (rear)
Brakes > Mechanical brake components > Brake discs and drums > Brake discs
 Rear 131 ×3.8 5.9% 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
Coil spring (front)
Suspension > Springs > Coil springs > Coil spring
 Front 72 ×121 3.2% Elevated
Service brake performance (rear)
Brakes > Brake performance > Service brake performance > Plate brake tester > Service brake performance
 Rear 23 ×7.0 1.0% Elevated
Service brake performance (rear)
Brakes > Brake performance > Service brake performance > Rbt > Service brake performance
 Rear 61 ×3.3 2.7% Likely
Ball joint (front)
Suspension > Suspension arms > Ball joint
 Front 38 ×2.7 1.7% Elevated
Brake discs (rear)
Brakes > Mechanical brake components > Brake discs and drums > Brake discs
 Rear 471 ×2.6 21.1% Wear
Engine oil leaks
Noise, emissions and leaks > Fluid leaks > Engine oil leaks
 Any 48 ×2.4 2.2% 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.

On this year, prefer the electric. The petrol cars passed first time 3.7 pp less often, on 6,581 tests.

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
2018 Zs +3.8 pp better 74.5% 4,845
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 2020 Zs

The items that failed 2020 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.

  • Tyres — Condition (front) — recorded on 14.5% of failed first attempts
  • Tread depth (front) — recorded on 9.8% of failed first attempts
  • Headlamp (front) — recorded on 9.7% of failed first attempts
  • Brake pads (front) — recorded on 7.3% of failed first attempts
  • Brake discs (rear) — recorded on 5.9% 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.

Electric Zs passed first time 3.7 pp more often than petrol ones (83.1% of 5,182 vs 79.4% of 6,581). In 2025, 81.0% of 11,763 first MOTs on the 2020 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 84.7%. Among 2,233 failed first-attempt MOT tests (test year 2025), Catalyst emissions appears more often than on similar cars (5.6% of…
Ranked by how often they were actually recorded, the items that failed 2020 MG Zss most often at the first attempt were Tyres — Condition (front) (14.5%), Tread depth (front) (9.8%) and Headlamp (front) (9.7%) — 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: Catalyst emissions (5.6% of those tests; 124 observed failures; about 7.7× more often than similar cars). These are statistical signals, not a diagnosis of any individual car.
Catalyst emissions shows up more often than on similar cars (5.6% of those tests; 124 observed failures; about 7.7× 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 2020 MG Zs include Catalyst emissions, Headlamp (front), Wheel bearings (front). 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 2020 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.

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