Engine management light: diesel vs petrol
Last updated · OBDCode UK editorial
A petrol engine-management-light fail and a diesel one are different physical faults. The split uses the same Class 4 certificate wording by fuel. The all-fuels follow-up is on the engine management light page.
A flashing engine light is Stop — do not drive it in; arrange collection or recovery. A steady engine light is drive with care until you have confirmed it is not flashing. Colour does not set drive advice. The steady / flashing decision hub is the existing engine management light guide.
What the 2024 fail cohort did next
The same-item rate is cars that failed this wording again in 2025, among every car that failed it at the first 2024 normal test. Cars not tested in 2025 stay in the denominator and count as not repeating. The extracts do not record the repair.
The not-tested gap is 11.5 percentage points more than cars that did not fail on this wording. It is a point, not an interval. A missing later test is not a scrappage flag.
Odometer change to the next annual MOT
Among cars with a valid MOT-to-MOT pair, the stored percentiles of odometer change from the 2024 index test to the next annual MOT. n is the pair count, not the fail cohort. These are points. They are not recomputed here, and they are not “miles driven with the light on”.
Published where the treated pair count is at least 500.
Scroll horizontally to read every mileage percentile.
| 2024 index test | Pairs | 10th | 25th | Median | 75th | 90th |
|---|---|---|---|---|---|---|
| Failed on this line | 307,838 | 1,535 | 3,421 | 6,251 | 9,991 | 14,564 |
| Did not fail on this line | 28,223,035 | 1,502 | 3,150 | 5,739 | 9,179 | 13,352 |
The median on this line is 512 miles above the control median (point).
Days until a later retest passed
Of the 329,193 cars that failed on this line and then passed a later 2024 retest, half did so within 1 days (point). That planning figure excludes same-day station rectification. The retest window count is 391,286 — it is not the headline fail cohort.
Among the 330,605 cars that came back for a later 2024 retest, 99.5% (95% CI 99.5–99.5) passed on the first completed attempt.
A passed retest is a passed retest. The extracts do not say the car was repaired. Day counts are published only when at least 300 cars passed a later 2024 retest.
Petrol vs diesel vs hybrid
Each row is that fuel only. It is not the all-fuels rate on the engine management light page. Hybrid is its own row. Do not average petrol and diesel.
A rate below 300 cars in that fuel cell prints as —.
Scroll horizontally to read every fuel column.
| Fuel | Cars | Same-item fail | Not-tested gap |
|---|---|---|---|
| Petrol | 192,397 | 15.4% (95% CI 15.3–15.6) | +15.6 pp |
| Diesel | 194,460 | 14.2% (95% CI 14.1–14.4) | +6.9 pp |
| Hybrid Electric (Clean) | 1,972 | 9.0% (95% CI 7.8–10.4) | +4.1 pp |
By age at the 2024 test
The table is crude — age is still in the number. The age-standardised rate beside it is a weighted sum of five age-specific rates on the Class 4 earliest-2024-NT known-age mix. That standardised figure is not a binomial and does not carry a Wilson interval. A band below 300 cars (crude) or 300 cars (standard) prints as —.
Age-standardised same-item fail: 13.9% (labelled age-standardised). Crude same-item fail: 14.8% (95% CI 14.7–14.9).
Scroll horizontally to read every age column.
| Age | Cars | Crude same-item | Age-specific rate |
|---|---|---|---|
| 3–5 years | 13,941 | 8.0% (95% CI 7.5–8.4) | 8.0% age-specific |
| 5–8 years | 57,502 | 12.4% (95% CI 12.1–12.7) | 12.4% age-specific |
| 8–12 years | 113,316 | 15.0% (95% CI 14.8–15.2) | 15.0% age-specific |
| 12–16 years | 98,121 | 15.9% (95% CI 15.6–16.1) | 15.9% age-specific |
| 16 years and over | 108,504 | 15.7% (95% CI 15.5–15.9) | 15.7% age-specific |
What else was on the same certificate
Other L0 wordings on certificates that already carry this lamp line. Rate = certificates with both ÷ certificates with the lamp. Cells below 500 certificates are omitted, not shown as zero.
391,289 certificates carried this lamp wording.
Scroll horizontally to read every co-occurrence column.
| # | Also on the certificate | Certificates | Share |
|---|---|---|---|
| 1 | Position lamp A lamp missing, inoperative or in the case of a multiple light source more than 1/2 not functioning | 37,647 | 9.6% (95% CI 9.5–9.7) |
| 2 | Headlamp aim The aim of a headlamp is not within limits laid down in the requirements | 37,439 | 9.6% (95% CI 9.5–9.7) |
| 3 | Tread depth worn close to legal limit/worn on edge | 35,716 | 9.1% (95% CI 9.0–9.2) |
| 4 | Windscreen washers not working or not providing sufficient fluid to clear the windscreen | 34,759 | 8.9% (95% CI 8.8–9.0) |
| 5 | Coil spring A spring or spring component fractured or seriously weakened | 27,918 | 7.1% (95% CI 7.1–7.2) |
| 6 | Brake pads wearing thin | 26,201 | 6.7% (95% CI 6.6–6.8) |
| 7 | Ball joint has slight play | 25,588 | 6.5% (95% CI 6.5–6.6) |
| 8 | Wipers Wiper blade missing or obviously not clearing the windscreen | 25,382 | 6.5% (95% CI 6.4–6.6) |
| 9 | Stop lamp missing, inoperative or in the case of a multiple light source more than 1/2 not functioning | 24,735 | 6.3% (95% CI 6.2–6.4) |
| 10 | A headlamp or light source missing, inoperative or more than ½ not functioning in the case of LED | 22,821 | 5.8% (95% CI 5.8–5.9) |
Models with the highest same-item fail rate
Among models with at least 200 cars in this fail cohort. Age-adjusted recurrence is used where that field exists on the row; otherwise the crude fail_same_rate is printed and labelled crude. Below the floor the rate is —.
Scroll horizontally to read every model column.
| # | Make and model | Cars | Same-item fail |
|---|---|---|---|
| 1 | Honda Cr-V | 2,554 | 22.1% (95% CI 20.6–23.8) crude |
| 2 | Mazda 3 | 2,125 | 22.1% (95% CI 20.4–23.9) crude |
| 3 | Jeep Renegade | 816 | 21.9% (95% CI 19.2–24.9) crude |
| 4 | Nissan Primastar | 210 | 21.9% (95% CI 16.8–28.0) crude |
| 5 | Suzuki Alto | 418 | 21.8% (95% CI 18.1–26.0) crude |
| 6 | Renault Twingo | 227 | 21.6% (95% CI 16.7–27.4) crude |
| 7 | Mazda 2 | 1,313 | 21.6% (95% CI 19.4–23.9) crude |
| 8 | Suzuki SX4 | 527 | 21.3% (95% CI 18.0–24.9) crude |
| 9 | Dacia Sandero | 800 | 21.1% (95% CI 18.4–24.1) crude |
| 10 | SEAT Altea | 291 | 21.0% (95% CI 16.7–26.0) crude |
| 11 | Subaru Forester | 376 | 20.7% (95% CI 17.0–25.1) crude |
| 12 | Ford Transit Courier | 548 | 20.4% (95% CI 17.3–24.0) crude |
Largest postcode areas in this fail cohort
Postcode area of the 2024 index test. Areas below 300 cars are omitted. Area PE is Peterborough, not petrol.
Scroll horizontally to read every postcode-area column.
| Postcode area | Cars | Same-item fail |
|---|---|---|
| B | 9,665 | 12.6% (95% CI 11.9–13.3) |
| CF | 8,745 | 17.7% (95% CI 17.0–18.6) |
| BS | 8,548 | 16.8% (95% CI 16.1–17.7) |
| G | 7,569 | 15.6% (95% CI 14.8–16.5) |
| NG | 7,470 | 14.7% (95% CI 13.9–15.5) |
| S | 6,915 | 12.7% (95% CI 11.9–13.5) |
| PO | 6,641 | 16.2% (95% CI 15.3–17.1) |
| LE | 6,403 | 11.7% (95% CI 10.9–12.5) |
Two-repeat and never-seen-again
Of 380,092 cars that failed this wording on their earliest 2023 annual test, 14.9% (95% CI 14.8–15.0) also failed on the same wording in 2024, and 3.8% (95% CI 3.7–3.8) failed on it in 2023, 2024 and 2025. This is consecutive years of the same certificate line, not a garage outcome.
Of 380,092 cars that failed this wording on their earliest 2023 annual test, 69.6% (95% CI 69.5–69.8) appear in the 2025 Class 4 extract at all (30.4% (95% CI 30.2–30.5) do not). The complement of seen_2025_rate is not_seen_2025_rate, not a gone rate. A missing later test is not scrappage.
Published where the 2023 origin is at least 500 cars.
How these figures are calculated
Window: first normal 2024 Class 4 test (test type NT) → 2025 outcome. The cohort is every vehicle whose index test failed this wording. The control is every other Class 4 vehicle whose index test did not fail this wording. Counts are test records. vehicle_id stability across annual extracts is an empirical finding, not a DVSA guarantee. Cars not tested in 2025 stay in the denominator and count as not repeating.
Floors stated on this page: cohort 500; model 200; age / fuel / postcode / band 300; age-standard band 300; miles pairs 500; returned 300; passed retest 300; three-year chain 500; co-occurrence 500.
Binomial rates print as a percentage with a 95% Wilson interval, or as —. Lifts, gaps, medians and percentiles stay points. Full method and the Replication section: how these figures are calculated.
Download the tables for edition 2026.1 from the dataset page.
These figures are a statistical association from the national MOT extracts. They are not a prediction about this car, and we have not inspected it.
Source: DVSA Anonymised MOT tests and results, 2024 and 2025 extracts (Class 4). Repeat rate = cars that failed on this wording again in 2025 ÷ unique cars that failed on it at their first 2024 normal test. Contains public sector information licensed under the Open Government Licence v3.0.