ISO 9128:2006

Overview

ISO 9128:2006 defines the graphical symbols and colours used on road vehicles to designate the correct brake fluid type. The standard aims to prevent the use of incompatible fluids (petroleum‑based vs non‑petroleum) that can cause catastrophic brake system failure. It applies to vehicle labelling and under‑bonnet identification of brake fluid reservoirs.

Key points: durable markings, clear placement near the filler cap, and standardised colour/symbol combinations for each fluid type.

Key Topics

• Scope and purpose

  • Identifies symbols and colours for: petroleum‑base brake fluid systems, non‑petroleum‑base brake fluid systems and silicone‑based brake fluids.
  • Emphasises that incompatible fluids are totally incompatible and can cause brake failure.

• Under‑bonnet applications

  • At least one appropriate symbol shall be clearly visible and obviously associated with the brake fluid reservoir.
  • Symbols must be permanently affixed, engraved or embossed within 100 mm of the brake fluid reservoir filler cap.
  • Minimum nominal dimension for symbols is 12 mm; larger sizes are recommended where space allows.

• Graphical symbol definitions

  • Petroleum‑base fluids: green equilateral triangle with red border and a central white oil drop.
  • Non‑petroleum brake fluids: yellow regular octagon with black border and a central black brake symbol.
  • Silicone‑based fluids: purple square with black border and the letters Si in white centred inside.
  • Symbols may be used with a deletion sign (full cross) to indicate "DO NOT USE". A symbol referencing the vehicle handbook or additional written information is permitted but must not appear inside the symbol boundary.

Applications

This standard is practical for: vehicle manufacturers, service and maintenance technicians, parts suppliers, and safety auditors. Practical applications include:

• Labelling reservoir caps and adjacent under‑bonnet surfaces to ensure correct brake fluid selection during servicing.
• Marking replacement fluid containers and service documentation to match vehicle markings (the same symbols are used for fluid containers as referenced in ISO 3871).
• Training materials and workshop procedures to reduce the risk of incompatible mixing and subsequent brake failure.

Benefits:

• Reduces risk of catastrophic brake system failure by preventing incorrect fluid use.
• Improves consistency of vehicle and container labelling internationally.
• Supports clear communication between manufacturers, technicians and end users.

Related Standards

• ISO 3871 - Labelling of containers for brake fluids (same symbols may be used on containers).
• ISO 4925 - Specifications for non‑petroleum (glycol) brake fluids.
• ISO 7308 - Petroleum‑based brake fluid for stored‑energy hydraulic brakes.

For implementers, follow ISO 9128:2006 when designing under‑bonnet markings and ensure durable, legible placement close to the filler cap to comply with the minimum dimensions and colour/symbol definitions.