MOT advisory explained
“Service brake fluctuating, but not excessively”
The braking force at one wheel rose and fell as the wheel turned, instead of holding steady. It nearly always means a disc or drum that is no longer even all the way round, and it is the same thing you feel as a pulse through the brake pedal.
On the roller brake tester the needle for one wheel, or both on an axle, swung up and down once per revolution while the pedal was held steady. The brake grips harder at one point of the disc’s rotation than at another. The swing was small enough to pass.
5.9% fail on the service brake at the next test. That is a moderate figure, because the cause is wear or corrosion of the disc surface, and that usually progresses slowly. It does not reverse unless the cause was a film of rust from standing.
Both sides, parts and labour, independent garage. Six in ten of these advisories are on the front axle. If the car had been standing before the test, try a week of normal driving first.
If the certificate also has “brake disc worn, pitted or scored” on the same axle, you have the cause and the effect on one page. The pitting is what the rollers felt.
A “service brake fluctuating, but not excessively” advisory means the roller brake tester showed braking force at a wheel rising and falling with each revolution, usually from a disc or drum with an uneven surface. The variation was within limits, so the car passes. New front discs and pads cost £200–£330 fitted at an independent garage. According to DVSA MOT data analysed by PriceMyRepair, 5.9% of 1.3 million such advisories followed to the next test failed on the service brake.
Why braking force goes up and down
Uneven thickness. People say a disc is warped. What has usually happened is that it is no longer the same thickness all the way round. A high spot a few hundredths of a millimetre proud is pinched harder by the pads on every pass. On the rollers that shows as a regular pulse. In the car it is a pedal that pushes back against your foot.
Patchy rust. A car that stands, especially after being put away wet, rusts its discs everywhere except under the pads. That leaves a pad-shaped patch with different grip from the rest of the disc. Light rust scrubs off in a few stops. Rust that has had months to pit the surface does not.
Drums. On cars and pickups with rear drum brakes, a drum that has gone slightly oval gives the same reading. It is less common, and it is why rear entries are in the minority.
Will it fail next year?
Two wordings cover this finding. Together they have been recorded 3,269,652 times, and 1,274,510 can be followed to the same car’s next MOT.
| What happened at the next test | Share |
|---|---|
| Failed on the same component | 5.9% |
| Failed on anything under defect 1.2.1 | 7.0% |
| Same advisory recorded again | 13.3% |
According to DVSA MOT data analysed by PriceMyRepair: 1,274,510 advisories followed to the same vehicle’s next test. Rows can overlap.
It fails less often than the other roller-test advisory, a binding brake, which is at 9.3%. Binding gets worse quickly because heat feeds it. Fluctuation is a surface problem and moves at the pace of disc wear.
It is rarely carried over. Only 13.3% are advised again. Some of those discs were replaced with the next pads. Others were on cars that had stood before the test, and a year of normal use cleaned the discs up.
| Advisory wording | Fails on same part | Advised again | Followed |
|---|---|---|---|
| Parking brake efficiency only just met. It would appear that the braking system requires adjustment or repair | 12.3% | 12.1% | 314,204 |
| Service brake binding | 9.3% | 14.4% | 2,418,487 |
| Brake pad(s) wearing thin | 7.2% | 16.9% | 13,888,197 |
| Service brake fluctuating, | 5.9% | 13.3% | 1,274,510 |
| Brakes imbalanced requirements only just met. It would appear that the braking system requires adjustment or repair | 4.8% | 6.4% | 690,135 |
| Brake disc worn, pitted or scored, | 3.7% | 31.2% | 15,014,091 |
| Brake disc worn, | 2.6% | 12.9% | 3,690,262 |
Both the advisory and its consequences rise steadily with age. It goes from 3.5 per 1,000 tests at 3–4 years to 13.3 at 20 years and over, and the share that fail next time doubles, from 3.4% to 7.3%.
| Age of car | Per 1,000 tests | Fails on same part | Followed |
|---|---|---|---|
| 3–4 years | 3.5 | 3.4% | 97,034 |
| 5–6 years | 5.0 | 4.3% | 141,173 |
| 7–9 years | 7.1 | 5.4% | 270,216 |
| 10–12 years | 9.4 | 6.6% | 281,767 |
| 13–15 years | 10.7 | 7.2% | 225,069 |
| 16–19 years | 11.4 | 7.3% | 149,780 |
| 20 years and over | 13.3 | 6.4% | 72,426 |
From about fifty miles an hour on a clear, dry road, brake gently and steadily and pay attention to your foot and your hands. A rhythmic push back through the pedal means the discs are uneven. A shake through the steering wheel as well means it is the front pair.
If you feel nothing, the fluctuation is small and may have been surface rust on the day. If you feel it clearly, it will not go away, and new discs are the cure.
Having discs skimmed is rarely worth it on an ordinary car. It often costs nearly as much as new discs and leaves them thinner, so they overheat and go uneven again sooner.
Exact wording on your certificate
The rollers give the tester a trace to read, and two phrasings are in use for the same small swing. A large swing is a failure.
| Line on the certificate | Result | Code |
|---|---|---|
| Service brake fluctuating, but not excessively | Advisory — pass | 1.2.1 (e) |
| Brake indicates slight fluctuation of brake effort | Advisory — pass | 1.2.1 (e) |
| Service brake excessively fluctuating | Major — fail | 1.2.1 (e) |
About six in ten are front brakes and testers often record just the axle. The front discs do most of the work and run hottest, and heat is what makes a disc wear unevenly. “both” is the most common note, because discs on an axle share a history.
| Position written by the tester | Share of all instances |
|---|---|
| Front | 23% |
| Offside front | 20% |
| Nearside front | 19% |
| Rear | 12% |
| Offside rear | 12% |
| Nearside rear | 11% |
From 3,269,652 recorded instances. Testers can add their own note after the standard wording. The most common on this advisory: “both” (93,423), “both sides” (57,444), “both front” (28,461), “both rear” (16,740), “nearside and offside” (9,704), “both fronts” (6,843), “n/s and o/s” (4,879), “both rears” (4,729).
What it costs to put right
| Job | Price fitted | Notes |
|---|---|---|
| Front discs and pads, both sides | £200–£330 | The normal cure for front fluctuation |
| Front pads only | £90–£150 | Does not cure it. The disc is the uneven part |
Independent garage prices for a typical car, fitted. Rear discs and pads usually cost a little less, and rear drums are priced by model. New pads alone will not fix a fluctuating brake and will bed in badly on an uneven disc. Prices for your model are on the brake pads and discs cost page.
Can I still drive with this advisory?
You may notice a slight pulse under gentle braking and nothing under hard braking. Plan new discs with the next pad change. Bring it forward if the pulsing becomes strong, the steering shakes when braking from speed, or stopping distances feel longer.
Enter your reg to see every brake advisory in your car’s MOT record. Pitted discs one year and a fluctuating brake the next is one fault developing, not two.
Which cars get this advisory most?
All vehicles together see this on 7.0 of every 1,000 tests. The models below see it around one and a half to two times as often.
| Model | Per 1,000 tests | Vs all cars | Tests |
|---|---|---|---|
| Saab 9-3 | 15 | 2.2× | 589,429 |
| Toyota Hilux | 15 | 2.1× | 734,628 |
| Mazda 6 | 14 | 2.0× | 728,629 |
| Nissan Navara | 13 | 1.9× | 712,261 |
| Mitsubishi L200 | 13 | 1.9× | 935,407 |
| Tesla (all models) | 13 | 1.9× | 477,606 |
| Volvo V70 | 12 | 1.8× | 542,743 |
| Mazda MX-5 | 11 | 1.6× | 962,840 |
| Kia Ceed | 11 | 1.5× | 1,221,714 |
| SEAT Ibiza | 11 | 1.5× | 2,030,031 |
Model families are grouped by the first word of the DVSA model name, so “Transit” covers every Transit variant. Only models with at least 60,000 tests are ranked.
Three pickups are on the list, the Toyota Hilux, Nissan Navara and Mitsubishi L200. They have drum brakes at the rear and tend to work in mud and water, which is hard on any braking surface.
Tesla (all models) is the most interesting entry. Electric cars slow down mainly through the motor, and their friction brakes can go days without being used in earnest. Discs that are not used rust, and rusty discs give an uneven reading on the rollers. The Mazda MX-5, a car that often stands through the winter, is probably there for a similar reason.
What to do next
- Drive it normally for a week and notice the pedal. If the car had stood before the MOT, a few firm stops may be all it needed.
- Find out which axle. The certificate often says front or rear. The steering wheel tells you if it does not: shake means front.
- Replace discs and pads together. Both sides of the axle. New pads on old uneven discs is money wasted.
- On an electric or hybrid car, use the brakes on purpose. A few firm stops from speed every week or two keeps the discs clean. Some cars have a setting that does it for you.
Service brake fluctuating advisory FAQ
What does service brake fluctuating, but not excessively mean?
On the roller brake tester, the braking force at a wheel rose and fell with each revolution instead of staying steady. The variation was within limits, so it is an advisory and the car passes.
What causes brake effort to fluctuate?
Usually a brake disc that has worn to an uneven thickness or has patchy corrosion, so the pads grip harder at one point in each turn. On rear drum brakes an oval drum does the same.
Will it fail the next MOT?
Sometimes. According to DVSA MOT data analysed by PriceMyRepair, 5.9% of 1.3 million such advisories failed on the service brake at the next test, and 13.3% were given the same advisory again.
How much does it cost to fix a fluctuating brake?
The cure is normally new discs and pads on that axle. For the front that costs £200–£330 fitted at an independent garage. These are estimates and final quotes come from garages.
Is it safe to drive with this advisory?
Yes. Braking efficiency met the standard. You may feel a light pulse through the pedal. Have it attended to sooner if the pulsing is strong or the steering shakes under braking.
Why do electric cars get this advisory?
They slow down mostly through the motor, so the brake discs are used lightly and rust. Rusty discs grip unevenly. Tesla models appear in the top ten for this advisory in DVSA data.
How these figures were calculated. According to DVSA MOT data analysed by PriceMyRepair, from the DVSA anonymised MOT test results (Open Government Licence v3.0): 350,943,111 tests. This advisory was recorded 3,269,652 times; 1,274,510 of those were followed to the same vehicle’s next test between 180 and 730 days later. “Fails on the same part” means a failure at that next test under the same defect code and naming the same component, on either side of the vehicle. Testers do not always name a component the same way twice, so the figure is a floor. Method and how to cite.