When preparing for your MOT test, many drivers focus on tyres, lights, or brakes. However, rust and corrosion are among the most significant yet overlooked reasons for MOT failures in the UK. While a bit of surface rust might not matter, severe corrosion in certain areas can lead to an outright failure. Understanding how rust impacts MOT results can help you avoid unnecessary costs and keep your vehicle roadworthy.

Why Rust Matters in an MOT

Rust weakens the structural integrity of a car. During an MOT, testers check whether corrosion affects key safety components. While surface rust on body panels is usually not an issue, corrosion that compromises the strength of the chassis, suspension, or braking system will almost certainly result in a fail.

The MOT is primarily about road safety. A corroded structure may collapse in an car accident, while rusted brake pipes or suspension mounts can fail unexpectedly, putting the driver, passengers, and other road users at risk.

Areas of the Car Most Affected by Rust

Certain parts of a vehicle are more prone to corrosion and are closely inspected during an MOT:

• Chassis and subframe – Rust here can weaken the vehicle’s structure.
• Suspension mounting points – Corrosion in these areas can compromise handling and stability.
• Brake pipes and fuel lines – Rust can lead to leaks, reducing braking efficiency or causing fuel hazards.
• Floor pan and sills – These are critical to the car’s strength and crash protection.
• Wheel arches – While often cosmetic, severe rust can spread to structural areas.

If corrosion is within 30cm of a major structural point or component, it will likely be marked as a dangerous defect.

How MOT Testers Assess Rust and Corrosion

MOT testers categorise rust in different ways:

• Advisory – Surface rust that doesn’t compromise safety but may need attention in future.
• Minor defect – Slight corrosion near a structural area but not enough to fail.
• Major defect – Corrosion that weakens structural integrity or safety systems.
• Dangerous defect – Severe rust that makes the car unsafe to drive.

A major or dangerous defect means an automatic MOT failure.

Preventing Rust-Related MOT Failures

The best way to avoid rust-related MOT problems is regular maintenance:

• Clean your car frequently, especially during winter when salt accelerates corrosion.
• Apply underseal or rust protection to exposed metal parts.
• Inspect high-risk areas, such as brake pipes and suspension mounts.
• Repair small rust patches early before they spread.
• Service your car annually, so mechanics can spot corrosion before it becomes a serious issue.

Final Thoughts

Rust and corrosion are silent threats to your car’s MOT outcome. While cosmetic rust won’t cause concern, corrosion that affects the chassis, brakes, or suspension is a serious safety issue. By keeping your car clean, applying protective treatments, and repairing rust early, you can prevent MOT failures and extend the life of your vehicle.