Model Reports 8 min read Updated 12 Jul 2026

MG Zs 2020: reliability & common MOT faults

Elevated MOT failure patterns for the 2020 MG Zs include Catalyst emissions (~7.7× peers) and Headlamp (front) (~6.1× peers). Based on UK DVSA open data for test year 2025 (2,232 failed first-attempt tests), compared with similar age and mileage peers. Available test years: 2024, 2025.

2,232 failed first-attempt tests · 11,763 first tests (test year 2025)

Standout pattern: Catalyst emissions — about 7.7× more often than on similar peer cars.

Key takeaways before you buy

  • Catalyst emissions: about 7.7× more often than similar cars
  • Headlamp (front): about 6.1× more often than similar cars

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 2,232 failed first-attempt tests in test year 2025.

Catalyst emissions

This failure pattern appears about 7.7× more often than on similar peer cars — recorded on 124 failed first-attempt tests; 5.6% of failed tests for this model year.

Any · 124 failures · ×7.7 vs similar cars · 5.6% of failed first tests · Strong pattern — appears far more often than similar cars

Headlamp (front)

This failure pattern appears about 6.1× more often than on similar peer cars — recorded on 217 failed first-attempt tests; 9.7% of failed tests for this model year.

Front · 217 failures · ×6.1 vs similar cars · 9.7% 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 58 ×14.1 2.6% Likely common fault pattern
2 Catalyst emissions
Noise, emissions and leaks > Exhaust emissions > Spark ignition > Catalyst emissions
 Any 124 ×7.7 5.6% Strong pattern — appears far more often than similar cars
3 Headlamp (front)
Lamps, reflectors and electrical equipment > Headlamps > Headlamp
 Front 217 ×6.1 9.7% Strong pattern — appears far more often than similar cars
4 Headlamp
Lamps, reflectors and electrical equipment > Headlamps > Headlamp
 Any 169 ×4.7 7.6% Likely common fault pattern
5 Rbt (sp)
Brakes > Brake performance > Parking brake efficiency (sp) > Rbt (sp)
 Any 99 ×4.3 4.4% Likely common fault pattern
6 Service brake performance (rear)
Brakes > Brake performance > Service brake performance > Rbt > Service brake performance
 Rear 78 ×3.9 3.5% Likely common fault pattern

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 Headlamp aim not tested (front)
Lamps, reflectors and electrical equipment > Headlamp aim > Headlamp aim not tested
 Front 37 ×9.0 1.7% Wear / usage pattern — not treated as a model design fault
2 Headlamp aim not tested
Lamps, reflectors and electrical equipment > Headlamp aim > Headlamp aim not tested
 Any 41 ×7.2 1.8% Wear / usage pattern — not treated as a model design fault
3 Brake discs (rear)
Brakes > Mechanical brake components > Brake discs and drums > Brake discs
 Rear 131 ×3.8 5.9% 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 Coil spring (front)
Suspension > Springs > Coil springs > Coil spring
 Front 72 ×121.0 3.2% Elevated vs peers
2 Service brake performance (rear)
Brakes > Brake performance > Service brake performance > Plate brake tester > Service brake performance
 Rear 23 ×7.0 1.0% Elevated vs peers
3 Service brake performance (rear)
Brakes > Brake performance > Service brake performance > Rbt > Service brake performance
 Rear 61 ×3.3 2.7% Likely common fault pattern
4 Ball joint (front)
Suspension > Suspension arms > Ball joint
 Front 38 ×2.7 1.7% Elevated vs peers
5 Brake discs (rear)
Brakes > Mechanical brake components > Brake discs and drums > Brake discs
 Rear 471 ×2.6 21.1% 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 ×2.4 2.2% Elevated vs peers
7 Brake discs
Brakes > Mechanical brake components > Brake discs and drums > Brake discs
 Any 31 ×2.2 1.4% Wear / usage pattern — not treated as a model design fault

FAQs

We do not show a single reliability score for the 2020 MG Zs on this page. Among 2,232 failed first-attempt MOT tests (test year 2025), Catalyst emissions appears more often than on similar peer cars (about 7.7× more often than peers; 124 observed failures; 5.6% of failed tests). Treat this as a pre-purchase checklist from DVSA open data — not a guarantee for any individual car.
Among failed first-attempt tests we surface patterns that appear more often than on similar peer cars. Top example: Catalyst emissions (about 7.7× more often than peers; 124 observed failures; 5.6% of failed tests). These are statistical signals, not a diagnosis of any individual car.
Catalyst emissions shows up more often than on similar peer cars (about 7.7× more often than peers; 124 observed failures; 5.6% of failed tests). That does not prove a causal design fault — age, mileage, and usage still matter. Treat it as a pre-purchase check point, not a manufacturer TSB.
Common MOT problem areas for the 2020 MG Zs include Catalyst emissions, Headlamp (front). These are elevated versus similar peer cars where lift clears our floors — 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 look elevated versus peers 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 elevated MOT failure patterns for the 2020 MG Zs (registration year) using UK DVSA open data for the selected test year. Patterns are ranked against similar age and mileage peers. It is a buyer checklist from MOT defect statistics — not a full service history or manufacturer TSB 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.
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.

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.

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See brand-wide MOT rankings and year guidance for MG (separate from this model-year report).