Corrosion, Prescribed areas:

Excessive corrosion, inadequate repair, fractures, modification or severe distortion in the supporting structure to fixing points for major components from the steering, suspension, brakes and seat belts, will result in test failure. These are called "prescribed areas" and must be free of serious corrosion within 30cm of the fixing point.  Any hole caused by corrosion in these areas will result in failure. Appendix "C" of the manual deals with prescribed areas.

Deciding what the "supporting structure" is can be difficult. Nearly every panel on a vehicle carrys some load but the main stresses are on and around the fixing points of that particular component e.g a suspension spring anchor point.  If removal of a particular section, such as a wing, would clearly have no affect on the strength of the panelling to which the component is fixed then it would not be considered to be part of the prescribed area. As a rule of thumb, seperate panels that are joined by welding are likely to be considered a constituent part of the prescribed area but a bolted panel may not be viewed in the same light.  However, it is safer to assume that a tester will fail any corrosion within 30cms of a fixing point and arguments about whether that area is a "prescribed area" will have to be taken up with VI via the appeal process (VT17 available at the MOT station).

The 30cm requirement is measured as "the crow flies" and not along the profile of the panel.

Double "skin" sections are treated as a single panel where there is no air gap between the two panels.

There is also the main structural elements of the vehicle to consider and these are dealt with in Testers Manual section 6.5. This is easily identified on vehicles which have a chassis to which the body is mounted. On monocoque constructions the main structural members have to be identified and this differs between vehicle designs. It's usually the box and sill sections that run down the vehicle length on each side. Areas of the main structure which do not have steering, suspension, brakes or seat belt components fitted to them within 30 cms of the corroded area are called "non-prescibed areas".

Prescribed areas can be anywhere on the body or chassis where items from steering, suspension, brakes or seat belts fit. So, parts of the main structure referred to above, may also be  "prescribed areas" and any corrosion etc is likely to fail. The remaining bits of any chassis or main structure must be sufficiently corroded etc to the extent they are likely to adversely effect the braking or steering of the vehicle.

A plan view of prescribed areas shows just how much of the vehicle is covered.

Corrosion check list:

Q. Is there excessive corrosion anywhere?
A. Yes
Q. is it in a prescribed area?
A. Yes - Fail

Q. Is there excessive corrosion anywhere?
A. Yes
Q. Is it on the "main structure"?
A. Yes
Q. Has it weakened the main structure so much that it adversely affects the brakes or steering?
A. Yes - Fail.  Otherwise pass and advise.

Q. Are there any sharp edges caused by damage or corrosion?
A. Yes - Fail.  Otherwise pass and advise.

Q. Is the corrosion on a "highly stressed" component (steering arm, suspension item etc)?
A. Yes.
Q. Has it seriously weakened it i.e by reducing its diameter etc?
A. Yes - Fail.  Otherwise pass and advise.

Point and click where your corrosion is