MOT advisory explained
“Macpherson strut corroded but not seriously weakened”
Of all the lines a tester can write about your front suspension, this is the one least likely to come back as a failure. There is a single place on a strut where rust is serious, and the rest is appearance.
A MacPherson strut is the tall unit behind each front wheel that combines the damper, the spring seat and the upper steering pivot. The tester found rust on its body and judged the steel underneath to be sound.
1.6% of these fail on the same strut at the next test. It is one of the lowest figures among the corrosion advisories, because a strut tube is thick and takes a very long time to weaken.
Per axle, fitted, independent garage. A strut is priced as a shock absorber because that is what it is. Replacement is only called for when the spring seat is rusting through or the damper inside has failed.
A strut with a rusty tube and a solid spring seat needs nothing. Check whether the same certificate mentions a corroded coil spring. The spring sits on that strut, fails more often, and is the cheaper part to change first.
A “MacPherson strut corroded but not seriously weakened” advisory means the tester found rust on a front suspension strut but judged it still strong, so the car passes. Nothing needs doing unless the rust is at the spring seat. If replacement is needed, a pair of struts costs £150–£360 fitted at an independent garage. According to DVSA MOT data analysed by PriceMyRepair, only 1.6% of 370,013 such advisories failed on the same strut at the next test.
A damper that is also part of the structure
Why it has its own line. On most cars the front strut is not just a shock absorber. It locates the wheel, the hub bolts to the bottom of it, and the whole unit turns when you steer. So the MOT treats it as a suspension component as well as a damper, and corrosion on it is recorded under the structural heading.
The tube. The main body is a thick steel tube. Surface rust on it is normal on a car past ten years old and takes far longer to matter than the car is likely to last. Flaking paint and brown scale on the tube are what this advisory usually describes.
The seat. Part way up, a pressed steel pan is welded on for the coil spring to sit in. It is thinner than the tube, it holds water and grit, and it carries the weight of that corner. A seat that rusts through can let the spring slip down onto the tyre. “spring seat” appears among the notes testers add, and if it is in yours, that is the part to have inspected.
Will it fail next year?
The record allows 370,013 of these advisories to be followed to the same car’s next MOT.
| What happened at the next test | Share |
|---|---|
| Failed on the same component | 1.6% |
| Failed on anything under defect 5.3.3 | 3.3% |
| Same advisory recorded again | 22.5% |
According to DVSA MOT data analysed by PriceMyRepair: 370,013 advisories followed to the same vehicle’s next test. Rows can overlap.
It sits at the quiet end of the corrosion advisories. Corrosion near a suspension mounting fails 10.2% of the time, a corroded coil spring 5.0%, a corroded suspension arm 3.0%. The strut is lower than all of them.
The second row, failures of any suspension component under the same code, is only 3.3%. A rusty strut is not even a good predictor of other corrosion failures nearby. Most of these cars simply carry on.
| Advisory wording | Fails on same part | Advised again | Followed |
|---|---|---|---|
| Suspension component mounting prescribed area is corroded | 10.2% | 24.2% | 1,521,106 |
| Coil spring corroded | 5.0% | 39.1% | 4,780,118 |
| Shock absorbers has slight external damage to the casing | 4.3% | 23.2% | 452,485 |
| 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 |
| Suspension component corroded | 0.4% | 27.4% | 282,271 |
The advisory tracks age closely and the risk does not. It goes from 0.4 per 1,000 tests at 5–6 years to more than ten times that on cars in their late teens. The failure rate stays under two in a hundred in every age band, peaking at 1.8%.
| Age of car | Per 1,000 tests | Fails on same part | Followed |
|---|---|---|---|
| 5–6 years | 0.4 | 1.2% | 12,753 |
| 7–9 years | 1.4 | 1.5% | 56,771 |
| 10–12 years | 3.3 | 1.8% | 102,933 |
| 13–15 years | 4.8 | 1.7% | 101,583 |
| 16–19 years | 5.6 | 1.6% | 69,168 |
| 20 years and over | 4.3 | 1.4% | 19,128 |
The figures say the strut will almost certainly be fine. They are an average over tubes and seats together, and the rare failures are concentrated in the seats. One look with the wheel off settles which kind you have.
If the seat is solid, you can stop thinking about this advisory. It will probably be written again next year and mean as little.
If the seat is thin or holed, replace the struts as a pair before the spring moves. A spring that drops off its seat can cut into the tyre.
Exact wording on your certificate
The strut itself and its mounting on the body each have a version of this line, and “damaged” is used as well as “corroded”. The failure wording changes the ending.
| Line on the certificate | Result | Code |
|---|---|---|
| Macpherson strut corroded but not seriously weakened | Advisory — pass | 5.3.3 (b) (i) |
| Macpherson strut mounting damaged but not seriously weakened | Advisory — pass | 5.3.3 (b) (i) |
| Macpherson strut mounting corroded but not seriously weakened | Advisory — pass | 5.3.3 (b) (i) |
| Macpherson strut damaged but not seriously weakened | Advisory — pass | 5.3.3 (b) (i) |
| Macpherson strut modified but not seriously weakened | Advisory — pass | 5.3.3 (c) (i) |
| Macpherson strut mounting modified but not seriously weakened | Advisory — pass | 5.3.3 (c) (i) |
| Macpherson strut corroded and seriously weakened | Major — fail | 5.3.3 (b) (i) |
Nearly nine in ten instances are at the front, which is where most cars have their MacPherson struts. The offside front is recorded a little more often than the nearside front, 40% against 36%.
| Position written by the tester | Share of all instances |
|---|---|
| Offside front | 40% |
| Nearside front | 36% |
| Front | 13% |
| No position recorded | 3% |
| Offside rear | 3% |
| Nearside rear | 2% |
From 1,198,596 recorded instances. Testers can add their own note after the standard wording. The most common on this advisory: “both” (41,519), “both sides” (22,850), “both front” (15,922), “nearside and offside” (7,292), “both fronts” (3,252), “x2” (2,804), “n/s and o/s” (2,638), “both side” (2,071).
What it costs if the struts do need replacing
| Job | Price fitted | Notes |
|---|---|---|
| Pair of front struts | £150–£360 | Only if the seat is failing or the damper is worn |
| Top mounts, added to the job | £40–£90 | Usually done at the same time |
| Alignment afterwards | £40–£60 | Needed, the strut sets the wheel angle |
Independent garage, parts and labour included. The old spring can usually be refitted to the new strut if it is in good condition. Prices for your model are on the shock absorber replacement cost page, which covers struts.
Can I still drive with this advisory?
Rust on a strut makes no noise and changes nothing about how the car drives. The only way to know more is to look at the spring seat with the wheel off, which a garage can do at a service.
Enter your reg to see every test on your car. If a coil spring advisory has appeared on the same corner, the two are worth reading together.
Which cars get this advisory most?
The all-vehicle rate is 1.6 per 1,000 tests. One model is in a class of its own.
| Model | Per 1,000 tests | Vs all cars | Tests |
|---|---|---|---|
| Saab 9-3 | 18 | 10.7× | 589,429 |
| Peugeot 107 | 10 | 6.3× | 1,292,695 |
| Suzuki SX4 | 10 | 5.9× | 418,443 |
| Toyota Yaris | 9 | 5.5× | 4,619,042 |
| Fiat Panda | 8 | 4.9× | 1,004,369 |
| Renault Kangoo | 8 | 4.9× | 700,467 |
| Citroen C1 | 8 | 4.8× | 1,686,560 |
| Toyota Auris | 8 | 4.6× | 1,541,174 |
| Toyota Aygo | 7 | 4.5× | 2,282,030 |
| Porsche Boxster | 7 | 4.5× | 309,679 |
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 Saab 9-3 gets this advisory 10.7 times as often as the average vehicle, well clear of anything else. Behind it come the Peugeot 107, Citroen C1 and Toyota Aygo, which are one design under three badges, and two more Toyotas, the Toyota Yaris and Toyota Auris.
These are mostly cars that last. They are still being tested at fifteen years and more, and the strut has been in the spray from the front wheel for all of them.
What to do next
- Have the spring seat looked at. Wheel off, a torch, one minute. It is the only question this advisory raises.
- Read the coil spring line if there is one. Spring and strut rust together. The spring is the part that breaks.
- Leave the tube alone. Surface rust on the strut body does not need treating and is not worth paying for.
- If replacing, do both sides and the top mounts. Struts go in pairs, and the mounts are already off.
MacPherson strut corroded advisory FAQ
What does MacPherson strut corroded but not seriously weakened mean?
The tester found rust on a front suspension strut and judged that the steel is still strong. It is an advisory, so the car passes and nothing has to be repaired.
Is a corroded MacPherson strut an MOT failure?
Only when the corrosion has seriously weakened it. That is uncommon. According to DVSA MOT data analysed by PriceMyRepair, 1.6% of 370,013 such advisories failed on the same strut at the next test.
Where does rust on a strut actually matter?
At the spring seat, the pressed steel pan welded to the strut that the coil spring sits in. If it rusts through, the spring can drop. Rust on the main tube is cosmetic.
How much does it cost to replace MacPherson struts?
A pair of struts costs £150–£360 fitted at an independent garage, top mounts add £40–£90, and alignment afterwards £40–£60. These are estimates and final quotes come from garages.
Is it safe to drive with a corroded strut?
Yes. It passed because it is still strong enough. There are no symptoms to listen for. Have the spring seat checked at the next service.
Which cars get this advisory most?
The Saab 9-3, at 10.7 times the average, followed by the Peugeot 107, Suzuki SX4 and Toyota Yaris. It is rare on cars under seven 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 1,198,596 times; 370,013 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.