MOT fail · manual section 8.2.1.2

Petrol exhaust emits clearly visible black smoke during acceleration

What this MOT fail means, how often testers record it and what garages charge per hour. From 130,233,413 DVSA MOT tests taken 2022 to 2025.

MOT data updated 28 September 2026

As a fail, per 100 MOTs (n=130,233,413)0.005

Most often at16 years

Times recorded6,920

Times recorded adds every DVSA code with this wording, so a test can record it more than once, for example on two wheels under separate codes.

What it means

This is a major defect: the car fails its MOT. A major defect may affect the car’s safety, put other road users at risk or harm the environment. The car fails its MOT and the defect must be repaired.

Before it reaches this point, testers often record it as an advisory: Petrol exhaust emits black smoke during acceleration.

Exhaust emissions are measured against limits for the car’s age and fuel, and the car is checked for fluid leaks and excessive noise.

The MOT inspection manual describes the defect (section 8.2.1.2) as:

emits excessive dense blue or clearly visible black smoke during acceleration which would obscure the view of other road users

Read this section of the MOT inspection manual on GOV.UK

The DVSA codes counted on this page: the manual item and the defect text as DVSA records them. The heading above joins the two, as a certificate does; the tester also adds the position, such as nearside front.
Result	Manual item	DVSA defect text	Records
Fail Major	Catalyst emissions	emits clearly visible black smoke during acceleration (8.2.1.2)	6,179
Fail Major	Non catalyst emissions	emits clearly visible black smoke during acceleration (8.2.1.2)	741

Got an MOT advisory or defect on a certificate? Paste it into the MOT advisory checker to see what it means.

How common it is by age

Testers record it most at 16 years: 0.017 per 100 MOTs (n=4,858,625 tests at that age).

Per 100 MOT tests of cars at each age, all makes. We show no figure below 20 tests.
Age	Fail per 100	Tests (n)
5 years	0	9,425,360
6 years	0.001	10,382,720
7 years	0.001	10,537,318
8 years	0.002	10,440,457
9 years	0.002	9,949,012
10 years	0.003	9,049,507
11 years	0.004	8,087,514
12 years	0.007	7,303,151
13 years	0.008	6,612,160
14 years	0.011	6,054,526
15 years	0.015	5,591,675
16 years	0.017	4,858,625
17 years	0.017	4,040,458
18 years	0.017	3,261,622
19 years	0.017	2,479,858
20 years	0.015	1,845,952
21 years	0.013	1,321,417
22 years	0.012	913,980
23 years	0.011	619,531
24 years	0.009	428,815
25 years	0.009	313,355

Repair and cost

We do not map this defect to one repair job, because the fix depends on the cause. Garages charge by the hour, so ask for a quote that lists labour time and parts.

Local garage labour, per hour (65 shops)£78

Local garage, middle half£70 to £96

Main dealer labour, per hour (62 shops)£156

Main dealer, middle half£144 to £174

Median hourly rate charged for car repairs, from 1,058 local garage and 953 main dealer price quotes collected by the ONS, September 2025 to August 2026. The same shops are priced each month, so the number of shops is the real sample.

Related MOT defects

Oil leak, but not excessive4.59 per 100
Malfunction indicator lamp inoperative or indicates a malfunction1.46 per 100
Transmission oil leak, but not excessive0.59 per 100
Petrol exhaust Lambda reading after 2nd fast idle outside specified limits0.52 per 100
Emissions not tested unable to be completed0.29 per 100
Diesel exhaust emissions exceed manufacturer's specified limit0.26 per 100
Petrol exhaust carbon monoxide content after 2nd fast idle exceeds manufacturer's specified limits0.20 per 100
Oil leaking excessively from engine0.12 per 100
Petrol exhaust emissions likely to be affected by an exhaust leak0.12 per 100
Petrol exhaust carbon monoxide content after 2nd fast idle exceeds default limits0.12 per 100

All nuisance: noise, emissions and leaks defects All MOT defects Car repair costs

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Source

Contains public sector information licensed under the Open Government Licence v3.0. Source: DVSA anonymised MOT test data, class 4 normal MOT tests, 2022 to 2025, and the MOT inspection manual published on GOV.UK. Prices: ONS consumer price inflation price quotes, September 2025 to August 2026, UK.

MOT data updated 28 September 2026. Prices updated 22 September 2026.

Not affiliated with or endorsed by DVSA or the Office for National Statistics. How we calculate these figures · Data sources