Model Reports 4 min read Updated 18 Oct 2026

MG ZR 2004: reliability & common MOT faults

In 2025, 65 in every 100 first MOTs on a 2004 MG ZR were passes.

Summary

With 522 first tests, there are too few to say whether the 2004 MG ZR differs from the model years either side. Treat the faults below as a checklist.

At a glance

How 522 first tests went in 2025.

Passed first time
65 in every 100
Did not pass first time
35 in every 100181 failed first-attempt tests
The typical car
21 yearsabout 80,598 miles
First tests counted
522

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 2004 MG ZR vehicles in 2025, not a prediction that any one car will have them. Faults are grouped by part of the car. They come from MOT defect codes, not manufacturer bulletins, recalls or a diagnosis of any one car.

Noise, emissions and leaks

One fault: petrol emissions (with catalyst), 2.2 times as often as on similar cars.

Figures below are measured across the 181 failed first attempts in 2025 that had a mileage recorded, which allows a like-for-like comparison.

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.

Petrol emissions (with catalyst)

Failed on 23 first tests2.2 times as often as similar carsPossible evidence

What it means

Emissions levels over the manufacturer's specified limits are Major, as are levels over default limits, which apply when no exact match is found for the vehicle. Dense blue or clearly visible black smoke at idle, held for a set period, is Major, except for certain older vehicles and two stroke engines where smoke is unavoidable. An induction or exhaust leak that could affect emissions levels is Major too.

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

Body and structure

One fault: drive shaft joints and boots (front), 2.1 times as often as on similar cars.

Drive shaft joints and boots (front)

Failed on 22 first tests2.1 times as often as similar carsPossible evidence

What it means

A constant velocity boot that is only severely deteriorated is Minor. It is Major once it is missing, split or insecure so that it no longer prevents the ingress of dirt. A transmission joint excessively worn is Major, and graded Dangerous when it is so worn it is likely to fail.

Data: UK MOT open data, 2025. 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
65in every 100
Passed on the first test.
Fixed at the station
7in every 100
Failed, then fixed at the test station the same day.
Failed
28in every 100
Did not pass, and were not fixed at the test station.

First-attempt pass 65.3% of 522 first tests (2025): only cars that passed first time count. Official-style pass 72.0%: cars fixed at the test station also count as a pass. The 7 fixed and the 28 not fixed make the 35 in every 100 that did not pass first time.

Same model, other years

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

YearPassed first timeFirst tests
200363 in every 100430
2004 This car65 in every 100522
200568 in every 100339

Newer cars are younger, so look for a jump rather than the climb. A year earlier (2024), when these cars were a year younger, 63 in every 100 passed first time.

FAQs

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

With 522 first tests, there are too few to say whether the 2004 MG ZR differs from the model years either side. Treat the faults below as a checklist. In 2025, 65.3% of 522 first MOTs on the 2004 MG ZR passed first time (PRS: items fixed at the station the same day, counted as a fail). The official-style rate including PRS is 72.0%. Among 181 failed first-attempt MOT tests (test year 2025), Petrol emissions (with catalyst) appears more often than on similar cars (12.7% of those tests; 23 observed failures; about 2.2× more often than similar cars). 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.
Among failed first-attempt tests we highlight patterns that appear more often than on similar cars. Top example: Petrol emissions (with catalyst) (12.7% of those tests; 23 observed failures; about 2.2× more often than similar cars). These are statistical signals, not a diagnosis of any individual car.
Petrol emissions (with catalyst) shows up more often than on similar cars (12.7% of those tests; 23 observed failures; about 2.2× 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 checkpoint, not a manufacturer service bulletin.
Common MOT problem areas for the 2004 MG ZR include Petrol emissions (with catalyst), Drive shaft joints and boots (front). These are the faults that stand out compared with similar cars, not a complete list of what can go wrong on any individual car.
This page highlights MOT failure patterns for the 2004 MG ZR (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.
  • 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.

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