The MOT Files

MOT defect file

Braking efficiency below requirement

Last updated

Quick answer

The vehicle did not achieve the required braking force on test. This is a failure item and needs diagnosis before further use.

Typical cost
£120–£450
DIY viability
Garage job
Roller brake tester efficiencies compared with MOT minimumsA zero-to-one-hundred per cent bar chart compares two measured brake efficiencies with their MOT minimums. Service brake efficiency measures 58 per cent and extends beyond its 50 per cent minimum, so it passes. Parking brake efficiency measures only 12 per cent and stops short of its 16 per cent minimum, so it fails. These are the usual minimum figures for most passenger cars, calculated against vehicle weight.Brake efficiency (% of vehicle weight)0%25%50%75%100%ServiceParking58% — pass12% — fail50% minimum16% minimumOne pass and one failure from the same test
For most cars, the service brake must achieve at least 50% efficiency and the parking brake at least 16%. Here the service brake passes at 58%, but the parking brake fails at 12%. Results are calculated from measured brake force against vehicle weight.

What you might notice

  • The car pulling to one side under braking, which is the classic sign of uneven effort across an axle
  • A longer stop than you expect, particularly from motorway speeds
  • A handbrake that needs several more clicks than it used to, or will not hold on a hill
  • Often nothing detectable from the driver's seat — the rolling road measures forces at each wheel that you cannot feel on the road

What causes it

  • A seized or partially seized calliper or wheel cylinder, so one wheel contributes little or nothing to the total
  • Rear drum brakes with glazed shoes, seized adjusters or a stretched handbrake cable
  • Friction surfaces contaminated by a leaking calliper seal, wheel cylinder or hub seal
  • Old brake fluid that has absorbed moisture, or a failing servo or split vacuum hose reducing pedal assistance

Advisory or failure?

This is a failure item with no advisory version. A car must record a service brake efficiency of at least 50% and a parking brake efficiency of at least 16%, and falling short of either is a major defect. It is also a major defect if the effort at one wheel is less than 70% of the effort at its partner on the same axle — an imbalance of more than 30% — even where the overall efficiency figure passes. Grading escalates to dangerous where the service brake achieves less than half the efficiency required, or where a steered axle is grossly imbalanced, because the car will pull hard to one side in an emergency stop.

Can you fix it yourself?

Garage job

Diagnosis needs a rolling road or a decelerometer to know which wheel is short and by how much; guessing from the driver's seat usually means replacing parts that were fine. The individual repairs behind the failure — pads, a cable, a calliper — are within reach of a competent home mechanic, but you cannot confirm the fix without a brake test, and the retest measures exactly the same numbers on the same machine.

What it costs

The band runs from a rear brake adjustment and a new handbrake cable at £120 to £180, through a calliper with pads and a disc at £250 to £350 per corner, up to hydraulic work and a full fluid change at the top. What pushes it up is a fault present at more than one corner, a seized bleed nipple that forces a whole calliper to be replaced rather than serviced, and rear electronic parking brakes, where the motorised calliper alone costs more than a conventional one. Budget £50 to £80 of diagnostic time before any parts are ordered.

What happens if you ignore it

A car that fails the brake test is, by definition, not stopping as well as the law requires, and the shortfall reveals itself in precisely the emergency you were hoping to avoid. Using the vehicle after the certificate expires is an offence on its own, and using one in a dangerous condition brings a fine and three penalty points, with an insurer entitled to take a dim view of a known defect after a claim. Mechanically, a seized calliper left dragging also destroys the pad and disc it is rubbing on, so a modest repair becomes a larger one within a few hundred miles.

Common questions

What brake efficiency do you need to pass an MOT?
At least 50% for the service brake and at least 16% for the parking brake, measured on the rolling road. Falling short of either is a major defect and there is no advisory version of this failure. It escalates to dangerous where the service brake manages less than half the efficiency required of it.
Why did my car fail the brake test when the brakes feel fine?
The rolling road measures the braking force produced at each individual wheel, which is not something you can feel from the driver's seat. One seized calliper or a glazed rear drum can contribute almost nothing while the other three wheels mask it, so the pedal still feels normal on the road even though the total falls short of the requirement.
How much brake imbalance is allowed on one axle?
Up to 30%. If the braking effort at one wheel is less than 70% of the effort at its partner on the same axle, that is a major defect even where the overall efficiency figure passes. A grossly imbalanced steered axle is graded dangerous, because the car will pull hard to one side in an emergency stop.
Can I fix low brake efficiency myself?
The individual repairs are within reach of a competent home mechanic, but the diagnosis is not. You need a rolling road or a decelerometer to know which wheel is short and by how much, and guessing from the driver's seat usually means replacing parts that were fine. You also cannot confirm the fix without a brake test, and the retest measures the same numbers on the same machine.
How much does it cost to fix a brake test failure?
It runs from £120 to £180 for a rear brake adjustment and a new handbrake cable, through £250 to £350 per corner for a calliper with pads and a disc, up to hydraulic work and a full fluid change at the top. A rear electronic parking brake costs more, because the motorised calliper is dearer than a conventional one. Allow £50 to £80 of diagnostic time first.

Cars this happens to most

Of every model with at least 2,000 tests in the DVSA data, these record braking efficiency below requirement on the largest share of their MOTs. Across all of them the typical rate is 0.5% of tests.

  1. Peugeot 1065.5%

    228 times in 4,178 tests

  2. Volkswagen LT4.7%

    116 times in 2,480 tests

  3. Citroen Saxo4.6%

    135 times in 2,906 tests

  4. Talbot Express4.0%

    191 times in 4,826 tests

  5. MG Mgf3.3%

    176 times in 5,296 tests

  6. Alfa Romeo Spider3.2%

    101 times in 3,135 tests

  7. Iveco Daily3.0%

    90 times in 2,951 tests

  8. Peugeot 3062.5%

    84 times in 3,419 tests

A high rate here is a property of the fleet as much as the car: these models skew old, and almost everything fails more with age. It is a reason to check the item on a used example, not proof the model is badly built. Models with fewer than 2,000 tests are left out because a rate drawn from a few hundred cars moves too much to rank.

Pass rates for every make and model

This is general guidance, not a diagnosis. The severity DVSA records depends on the specific fault found, so the same item can appear as an advisory on one test and a failure on another. Ask a qualified tester or mechanic to inspect the vehicle.

Has this been recorded on your car?

Check the full MOT history for any UK registration.

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