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Technical Guide

MOT Advisories Explained: Defect Severity Levels

Updated: May 2026 • 4 min read

During an annual roadworthiness inspection in the UK, a vehicle can pass its evaluation while still being flagged with several advisory notes or minor defects. These logs are added directly to the official registry by the inspecting technician to notify the owner of components that are wearing down and will require mechanical attention in the near future.

Understanding the Defect Classifications

The checking framework uses a standardized tier system to group mechanical component issues based on how heavily they impact road safety:

The Immediate Fail Classifications

Unlike advisories, any component flagged with a Major or Dangerous defect results in an immediate test failure. A Dangerous defect indicates that driving the vehicle presents a critical, immediate threat to life, making it illegal to drive the car on public roads until repairs are complete.

How Advisories Affect Used Car Values

Reviewing historical testing logs provides a clear window into how well a used vehicle has been maintained. Seeing identical component advisories—such as engine oil leaks or worn suspension bush links—appear across consecutive years shows that the previous owner delayed regular workshop maintenance.

Additionally, multiple active advisories mean you should budget for upcoming repair costs, as things like replacing worn brake discs or matching tire sets across an axle will require financial investment shortly after purchase.

Scan Historical Test Advisories Instantly

Uncover hidden mechanical wear patterns and complete pass/fail defect histories before negotiating with a seller.

Audit Test History

Using Advisories to Negotiate Better Prices

When shopping for a used car, do not overlook the advisory list. You can use a detailed breakdown of upcoming maintenance items—such as a worn exhaust mounting or slightly pitted brake pipes—as a practical negotiating tool to lower the final purchase price, balancing out the costs of the repairs your new car will need.