MOT advisory explained
“Suspension arm corroded but not seriously weakened”
The suspension advisory least likely to fail you next year, and the one most likely to be written down again. Here is when rust on an arm matters and when it is just rust.
The tester saw rust on a suspension arm and judged that the metal underneath is still sound. It is a note about the surface. Nothing is loose, nothing moves that should not, and the arm is doing its job.
Of 1.4 million of these advisories followed to the next test, 3.0% failed on the same arm. More than a third were simply advised again. Most cars carry this line for years.
The price is for a replacement arm, per corner, fitted, if it ever comes to that. At the advisory stage a wire brush and a rust treatment are usually all it needs.
This is not a reason to replace an arm today. If a garage quotes for new arms on the strength of this line alone, ask them to show you metal that has actually thinned. A different line, “pin or bush worn”, is the one that means wear.
A “suspension arm corroded but not seriously weakened” advisory means the tester found rust on a suspension arm but judged the metal still strong, so the car passes. No repair is needed straight away. If the corrosion spreads, a replacement arm costs £140–£280 per corner at an independent garage. According to DVSA MOT data analysed by PriceMyRepair, only 3.0% of 1.4 million such advisories followed to the next test failed on the same arm.
Surface rust or weakened metal
What the tester is judging. Suspension arms are pressed or cast steel, and they live in road spray. Rust on them is normal on an older car. The tester taps and probes it. If the metal is solid under the rust, it is an advisory. If it flakes away, has holes, or has visibly lost thickness, it fails.
Where it matters most. Rust on the flat middle of an arm is rarely a problem. The places to look at are the ends: the housing that holds the bush, and on some rear arms the cup the spring sits in. Those are thin, they trap water, and they carry the load.
Same salt, other parts. A car with this advisory has usually had the same winters underneath everything else. Check the certificate for corroded brake pipes as well. That line fails far more often and is the better place to spend money first.
Will it fail next year?
There is a measured answer. The DVSA record follows each advisory to the same car’s next MOT, and this wording has been followed 1,384,389 times.
| What happened at the next test | Share |
|---|---|
| Failed on the same component | 3.0% |
| Failed on anything under defect 5.3.3 | 4.6% |
| Same advisory recorded again | 35.7% |
According to DVSA MOT data analysed by PriceMyRepair: 1,384,389 advisories followed to the same vehicle’s next test. Rows can overlap.
Among the corrosion advisories below this is one of the calmest. A corroded coil spring fails 5.0% of the time, because springs snap. Corrosion near a suspension mounting fails 10.2% of the time, because that is the body of the car and it cannot be unbolted. An arm is thick, and it takes a long time to rust through.
The other figure tells the rest of the story. 35.7% of these advisories are recorded again at the next test, unchanged. Owners leave it, testers note it again, and the arm carries on.
| Advisory wording | Fails on same part | Advised again | Followed |
|---|---|---|---|
| Suspension component mounting prescribed area is corroded | 10.2% | 24.2% | 1,521,106 |
| Brake pipe corroded, covered in grease or other material | 10.1% | 44.4% | 7,889,073 |
| Suspension arm pin or bush worn | 7.4% | 29.3% | 8,344,577 |
| Coil spring corroded | 5.0% | 39.1% | 4,780,118 |
| Suspension arm corroded | 3.0% | 35.7% | 1,384,389 |
| Sub-frame corroded | 2.0% | 39.8% | 2,445,675 |
| Macpherson strut corroded | 1.6% | 22.5% | 370,013 |
This is an old-car advisory. It barely exists at 5–6 years, at 0.6 per 1,000 tests, and reaches 23.3 per 1,000 on cars of 20 years and over. The chance of it turning into a failure stays low at every age and tops out at 3.5%, at 13–15 years.
| Age of car | Per 1,000 tests | Fails on same part | Followed |
|---|---|---|---|
| 5–6 years | 0.6 | 0.7% | 18,370 |
| 7–9 years | 3.9 | 2.1% | 155,264 |
| 10–12 years | 11.9 | 3.0% | 362,966 |
| 13–15 years | 20.1 | 3.5% | 420,269 |
| 16–19 years | 24.6 | 3.0% | 309,356 |
| 20 years and over | 23.3 | 2.3% | 106,623 |
A low failure rate means the rust is slow. It does not mean it stops. Steel that is left bare keeps rusting, and the advisory that costs nothing to deal with this year is the arm that needs replacing several winters from now.
The cheap moment is now. Cleaning back to metal and sealing it takes an hour on a ramp and can be done at the next service.
If the same line comes back year after year with a longer note each time, such as “heavily” or “flaking”, the tester is telling you it is getting closer to a fail.
Exact wording on your certificate
Several lines share this code. They all describe an arm, or the bracket it bolts to, that is marked but still strong. The failure uses almost the same words with the opposite ending.
| Line on the certificate | Result | Code |
|---|---|---|
| Suspension arm corroded but not seriously weakened | Advisory — pass | 5.3.3 (b) (i) |
| Suspension arm attachment bracket/mounting corroded but its strength is not seriously reduced | Advisory — pass | 5.3.3 (b) (i) |
| Suspension arm damaged but not seriously weakened | Advisory — pass | 5.3.3 (b) (i) |
| Suspension arm attachment bracket/mounting damaged but its strength is not seriously reduced | Advisory — pass | 5.3.3 (b) (i) |
| Suspension arm attachment bracket modified but not seriously weakened | Advisory — pass | 5.3.3 (c) (i) |
| Suspension arm attachment bracket/mounting slightly loose | Advisory — pass | 5.3.3 (a) (i) |
| Suspension arm corroded and seriously weakened | Major — fail | 5.3.3 (b) (i) |
Unlike most suspension advisories this one has no favourite corner. Front and rear, nearside and offside appear in almost equal shares, and testers often write “both” or “all”. Rust does not pick a side.
| Position written by the tester | Share of all instances |
|---|---|
| Offside rear | 13% |
| Nearside rear | 13% |
| Offside front | 13% |
| Nearside front | 11% |
| Rear | 11% |
| Front | 6% |
From 5,190,111 recorded instances. Testers can add their own note after the standard wording. The most common on this advisory: “both” (210,115), “both sides” (170,622), “all” (76,057), “trailing arm” (45,022), “both front” (35,698), “nearside and offside” (35,006), “both side” (25,304), “all arms” (22,831).
What it costs, if it comes to a repair
| Job | Price fitted | Notes |
|---|---|---|
| Replacement arm, one side | £140–£280 | Only once the metal is weakened |
| Arms both sides, same axle | £250–£480 | They rust at the same rate |
| Alignment afterwards | £40–£80 | Needed after any arm is changed |
Fitted prices at an independent garage. Treating surface rust is a small labour job and many garages will do it during a service if asked. Arm prices for your model are on the suspension repair cost page.
Can I still drive with this advisory?
There is nothing to listen or feel for with this advisory. It has no symptoms. The only check that means anything is a look on a ramp once a year, which the MOT already gives you.
Enter your reg to see every advisory from every test on your car, including how many years this one has been repeated.
Which cars get this advisory most?
The average across all vehicles is 9.0 per 1,000 tests. A handful of models sit far above that.
| Model | Per 1,000 tests | Vs all cars | Tests |
|---|---|---|---|
| Toyota Avensis | 57 | 6.4× | 878,561 |
| Mazda 6 | 47 | 5.3× | 728,629 |
| Mazda 3 | 40 | 4.4× | 1,145,262 |
| Toyota Corolla | 39 | 4.3× | 1,166,652 |
| Volkswagen Scirocco | 38 | 4.2× | 497,694 |
| Mazda MX-5 | 36 | 4.0× | 962,840 |
| Ford S-Max | 36 | 4.0× | 833,176 |
| Skoda Yeti | 35 | 3.9× | 722,116 |
| Ford Mondeo | 33 | 3.7× | 2,546,739 |
| Land Rover Freelander | 29 | 3.2× | 1,480,990 |
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.
The pattern is about steel and paint more than weight. The Toyota Avensis gets this advisory 6.4 times as often as the average vehicle, and Mazda and Toyota models from the same era fill half the list. These are cars that tend to outlast their underbody protection: mechanically they keep going, so they are still being tested at an age when the arms have had fifteen winters.
On one of these models the advisory is routine. It is still worth treating, because a replacement arm on an older car can mean seized bolts and extra labour.
What to do next
- Look at it, or ask for a photo. Surface rust is brown and rough but solid. Trouble looks like layers lifting, swelling around a seam, or metal you could push a screwdriver into.
- Have it cleaned and sealed. Wire brush, rust converter, then a wax or underbody coating. Ask for it at the next service. It is the whole repair at this stage.
- Check the rest of the certificate. Corroded brake pipes or corrosion near a mounting on the same car matter more than this line and should be dealt with first.
- Keep the wording from each year. If the tester’s note gets stronger from one MOT to the next, budget for the arm before it becomes a fail.
Suspension arm corroded advisory FAQ
Is a corroded suspension arm an MOT fail?
Only if the corrosion has seriously weakened the arm. Rust that leaves the metal sound is recorded as an advisory and the car passes. The failure wording is “corroded and seriously weakened”.
Will a corroded suspension arm fail next year?
Rarely. According to DVSA MOT data analysed by PriceMyRepair, 3.0% of 1.4 million such advisories failed on the same arm at the next test, and 35.7% were simply advised again.
Do I need to replace a corroded suspension arm?
Not at the advisory stage. Cleaning the rust back and sealing the metal is enough. Replacement is for an arm that has lost thickness, has holes, or is rusting through at a bush housing or spring seat.
How much does a suspension arm cost to replace?
A replacement arm costs £140–£280 per side fitted at an independent garage, plus £40–£80 for alignment. These are estimates and final quotes come from garages. On older cars seized bolts can add labour.
Is it safe to drive with a corroded suspension arm?
Yes. An arm that is corroded but not weakened is still strong enough, which is why it passed. There are no symptoms to watch for. Have it looked at on a ramp once a year.
Which cars get the suspension arm corroded advisory most?
The Toyota Avensis, at 6.4 times the average rate, followed by the Mazda 6, Mazda 3 and Toyota Corolla. It is mostly seen on cars over ten years old.
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 5,190,111 times; 1,384,389 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.