MG 3 2021: reliability & common MOT faults

At a glance

How 1,868 first tests went in 2025.

Passed first time: 82 in every 100
Did not pass first time: 18 in every 100334 failed first-attempt tests
The typical car: 4 yearsabout 23,869 miles
First tests counted: 1,868

What failed most often

Tyre condition (front)18 in every 100 failed tests

How we count this. Data: UK MOT open data, 2025. Only Class 4 cars on their first MOT of the year are counted. A car that fails and is fixed at the test station still counts as a fail in the first-attempt rate. These are raw results, not adjusted for age, mileage, or peer mix. The MOT does not test engine or gearbox internals.

Note:

These are patterns across 2021 MG 3 vehicles in 2025, not a prediction that any one car will have them. Faults are grouped by part of the car. A wear pattern follows age and use more than the way the car was built. They come from MOT defect codes, not manufacturer bulletins, recalls or a diagnosis of any one car.

Lamps and electrical

One wear pattern: headlight aim (front), 2.1 times as often as on similar cars.

Figures below are measured across the 331 of 334 failed first attempts (99.1%) that recorded an odometer reading in 2025. Mileage is needed to compare like with like.

We only list faults with at least 20 failures and a rate of about 2.0 times that of similar cars, which keeps one-off results out of the list.

Headlight aim (front)

Failed on 45 first tests2.1 times as often as similar carsWear pattern

What it means

Beam aim too high, too low or off to either side is Major. Where a driver's beam aim control is fitted, the aim is tested without altering the setting, and rechecked at the highest setting only if it would fail for being too low. Masks or converter kits on right hand dip headlamps are acceptable.

Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.

Advisories

Other things testers noted as worn or close to failing, more often than on similar cars.

An advisory is a note from the tester about something that has not failed yet. It is an early warning, not a fail.

Brake pads (front)

Noted on 45 first tests2.3 times as often as similar carsWear pattern

Brake discs (front)

Noted on 55 first tests2.1 times as often as similar carsWear pattern

Data: UK MOT open data, 2025. Counts cover advisories recorded on failed first tests only, compared with cars of the same age and mileage.

MOT pass rates

How first tests ended, and how the pass rates are counted.

Passed first time: 82in every 100; Passed on the first test.
Fixed at the station: 6in every 100; Failed, then fixed at the test station the same day.
Failed: 12in every 100; Did not pass, and were not fixed at the test station.

First-attempt pass 82.1% of 1,868 first tests (2025): only cars that passed first time count. Official-style pass 87.7%: cars fixed at the test station also count as a pass. The 6 fixed and the 12 not fixed make the 18 in every 100 that did not pass first time.

Same model, other years

Passed first time in every 100, all tested in 2025.

Newer cars are younger, so look for a jump rather than the climb. A year earlier (2024), when these cars were a year younger, 85 in every 100 passed first time.

Year	Passed first time	First tests
2014	67 in every 100	1,443
2015	65 in every 100	2,139
2016	71 in every 100	2,888
2017	69 in every 100	2,714
2018	72 in every 100	2,441
2019	75 in every 100	3,477
2020	79 in every 100	2,366
2021 This car	82 in every 100	1,868
2022	85 in every 100	3,999

FAQs

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

Is the 2021 MG 3 reliable?

The 2021 MG 3 follows the pattern of the model years either side. Its main cause of failure was Tyre condition (front), about 18 in every 100 failed tests. In 2025, 82.1% of 1,868 first MOTs on the 2021 MG 3 passed first time (PRS: items fixed at the station the same day, counted as a fail). The official-style rate including PRS is 87.7%. Among 334 failed first-attempt MOT tests (test year 2025), we highlight MOT failure patterns that show up more often than on cars of a similar age and mileage when the sample is large enough to trust. There is no single reliability score here; this is a pre-purchase checklist built from DVSA open data, not a guarantee for any individual car.

What is most likely to fail on a 2021 MG 3?

Ranked by how often they were actually recorded, the items that most often failed a 2021 MG 3 at the first attempt were Tyre condition (front) (17.5%), each as a share of the year's failed first attempts. That is what goes wrong most often on the car. The common faults table shows a different measure: faults that are unusual compared with similar cars.

How should I read advisories vs fails?

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.

What does this MG 3 2021 MOT report cover?

This page highlights MOT failure patterns for the 2021 MG 3 (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.

Does this include engine and gearbox problems?

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.
If the data for a car is too thin to say anything useful, we say so rather than guess.

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