Model Reports
8 min readUpdated 11 Sep 2026
DVSA open data · 1,901 tests analysed
Porsche Boxster 2004: reliability & common MOT faults
465 first-attempt MOT failures were recorded on the 2004 Porsche Boxster in 2025. Figures are among first-attempt failed MOT tests, not among all tests.
Catalyst emissions was the most common reason a 2004 Boxster failed its MOT — 31.9% of its failed first attempts.
First-attempt pass
75.5%
of 1,901 first tests (2025)
First tests
1,901
test year 2025
Failed first attempts
465
failed first-attempt tests
MOT pass rates
First-attempt and official-style rates among class 4 first tests of the year.
First-attempt pass
75.5%
of 1,901 first tests (2025)
Official-style pass
79.3%
incl. same-day PRS fixes
First tests
1,901
class 4 · first MOT of the year
Typical age 21.0 yrs · median mileage 77,031 mi
vs 2024:
+1.0 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 464 of
465 failed first attempts
(99.8%) that recorded an odometer reading in 2025 —
the subset the age-and-mileage comparison can be computed on.
Standout: Catalyst emissions — 31.9% of this year's failed first attempts
Recorded on 148 of those tests. It tops the table on elevation — about 5.3× more often than on similar cars of the same age and mileage. On this year it is also the commonest failure, so it answers both questions at once. The full ranked list is in the table below.
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.
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.
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.
Nothing separates this year from the Boxsters either side of it, so buy on the individual car. The checks below are the items that actually failed 2004 Boxsters, commonest first.
What to check on a 2004 Boxster
The items that failed 2004 Boxsters 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.
Catalyst emissions — recorded on 31.9% 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.
Catalyst emissions was the most common reason a 2004 Boxster failed its MOT — 31.9% of its failed first attempts. In 2025, 75.5% of 1,901 first MOTs on the 2004 Porsche Boxster passed first time (PRS — items fixed at the station the same day — counted as a fail). The official-style rate including PRS is 79.3%. Among 465 failed first-attempt MOT tests (test year 2025), Catalyst emissions appears more often than on si…
Ranked by how often they were actually recorded, the items that failed 2004 Porsche Boxsters most often at the first attempt were Catalyst emissions (31.9%) — 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 (31.9% of those tests; 148 observed failures; about 5.3× 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 (31.9% of those tests; 148 observed failures; about 5.3× 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 2004 Porsche Boxster include Catalyst emissions, Rigid brake pipes, Coil spring (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 2004 Porsche Boxster (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.
20242025
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.