Brake pipe corrosion on an MOT: what it means for a buyer
How MOT testers grade corroded brake pipes, from an advisory to a dangerous fail, why a repeat advisory is worth negotiating on, and which invoice to ask for.
Updated
Corroded brake pipes are a common line in a used car's MOT history. Slight corrosion usually earns an advisory, which means the car passed but the tester wants you to keep an eye on it. Excessive corrosion is a major defect and fails the car. A pipe at imminent risk of failing, or a leaking hydraulic pipe, is dangerous and the car should not be driven. For a buyer, a brake pipe advisory that comes back year after year is a fair reason to negotiate, and the invoice for any replacement is the evidence you want to see.
What brake pipes do and why they corrode
Rigid brake pipes are the thin metal lines that carry brake fluid from the master cylinder under the bonnet to each wheel. They run along the underside of the car, where they meet water, road salt and grit for years on end. Over time the outer surface rusts. If the rust eats far enough into the wall of the pipe, the pipe can split under the pressure of hard braking.
That is why testers take corrosion seriously. A failed brake pipe can mean a sudden loss of braking.
How MOT testers grade brake pipe corrosion
The rules are in item 1.1.11 of the DVSA inspection manual, rigid brake pipes. The tester looks at every visible length of pipe. If dirt hides the surface, they may scrape it lightly with a specialist tool, taking care not to damage any protective coating.
The manual sets out these defects:
| What the tester finds | Category | Result |
|---|---|---|
| Pipe at imminent risk of failure or fracture | Dangerous | Fail |
| Leaking pipe or connection on a hydraulic system | Dangerous | Fail |
| Pipe damaged or excessively corroded | Major | Fail |
| Pipe likely to become detached or damaged | Major | Fail |
| Pipe inadequately clipped or supported | Minor | Pass, recorded |
Where "excessively corroded" starts
The manual gives a guide: chafing, corrosion or damage that reduces the pipe's wall thickness by a third, about 0.25mm on a typical hydraulic brake pipe, justifies rejection. It also accepts this is not easy to judge, and tells testers to give the benefit of the doubt when they are not sure.
Advisories
Below that level, the tester can record an advisory. The manual says an advisory is used when an item is not bad enough to justify rejection, to let the presenter know. Typical wording in a car's MOT history reads along the lines of "brake pipe slightly corroded", sometimes with the location, such as front, rear or nearside.
An advisory is not a fail. The car passed. But corrosion does not reverse, so an advisory one year often becomes a fail a year or two later unless the pipe is replaced.
Reading a brake pipe advisory as a buyer
When you read a car's MOT history, look at how the brake pipe entries change over time.
- One advisory, then nothing. The pipe may have been replaced. Ask for the invoice.
- The same advisory several years running. The pipe is still on the car and still corroding. It has not failed yet, but it is closer every year.
- An advisory followed by a fail, then a pass. Repair work was done. Ask what was replaced and see the invoice.
- A fail for excessive corrosion with no record of a fix. Ask what happened. A car cannot pass a retest with the same defect.
Our MOT advisory checker explains common advisory wording. Our MOT fail rate pages show how often each model fails on brakes by age in Great Britain, which tells you whether brake problems are typical for the model.
Why the invoice matters
Brake pipes are often replaced in sections rather than all at once. A garage may replace the length that failed and leave the rest. So "brake pipes done" can mean anything from one short section to every pipe on the car.
Ask the seller for the invoice and look for:
- which pipes or sections were replaced (front, rear, a specific side or the full set);
- the date and the mileage, so you can match the work to the MOT history;
- the name of the garage, so the work can be checked if needed;
- whether the brake fluid was changed or the system bled at the same time.
If there is no invoice, treat the work as unproven. A mechanic on a ramp can usually see which pipes are new and which are original.
Using a repeat advisory to negotiate
A brake pipe advisory is a known future cost, so it is a reasonable thing to raise when you agree a price. Keep it factual.
- Point to the MOT history and the year the advisory first appeared.
- Ask whether the pipes have been replaced since. If they have, ask for the invoice.
- If they have not, get a quote for the work from a garage before you make an offer. Ask whether the quote covers one section or the full set.
- Offer a lower price that reflects the quote, or ask the seller to have the work done and show you the invoice before you pay.
We do not give repair prices here, because they vary with the car, the layout of the pipes and the garage. Get a written quote for the specific car.
If the corrosion is bad enough that the next MOT is likely to fail, factor in the cost of the retest too. Our guide to buying a car that failed its MOT covers that situation.
What to check at a viewing
You will not see much without a ramp, but a few checks help.
- Look under the car with a torch near the rear wheels and along the sills, where pipes often run. Heavy flaking rust on the pipes is a warning sign.
- Check the brake fluid level under the bonnet. A low level can point to a leak.
- Look for damp patches on the inside of the wheels or on the ground under the car.
- On the test drive, the pedal should feel firm and stay firm. A pedal that sinks slowly when you hold it down is a reason to stop and have the car checked.
If the brake pipe history is long or the car is older and has lived near the coast or on salted roads, see the car and ask a mechanic to look underneath.
Frequently asked questions
Will corroded brake pipes fail an MOT?
Excessively corroded brake pipes are a major defect and fail the test. Slight corrosion usually gets an advisory and the car passes. A pipe at imminent risk of failure is a dangerous defect.
What does "brake pipe slightly corroded" mean?
It means the tester saw corrosion on a brake pipe that was not bad enough to fail. The car passed, but the corrosion is likely to get worse. Ask whether the pipe has been replaced since.
Can I drive a car with a dangerous brake pipe defect?
GOV.UK says you can only take a car away after a fail if its current MOT is still valid and no dangerous problems were found. A dangerous defect must be repaired first, and driving with one can bring a fine of up to £2,500, a driving ban and 3 penalty points.
Should I walk away from a car with a brake pipe advisory?
Not on that alone. It is a known future repair. Ask for invoices, get a quote and negotiate. Walk away if the seller cannot explain repeat fails or will not let a mechanic look underneath.