ISO 26262 Explained: Functional Safety for Automotive Engineers

What the standard covers

ISO 26262 is the international standard for functional safety of electrical and electronic (E/E) systems in series-production road vehicles. Its goal is to reduce unreasonable risk caused by malfunctions — a sensor that fails, software that behaves incorrectly or hardware that degrades. It covers the whole lifecycle, from concept to production, operation and decommissioning.

Hazard analysis and risk assessment

Everything starts with the item definition and the HARA (hazard analysis and risk assessment). For each hazardous event, engineers rate three factors:

• Severity (S): how bad the potential harm is.
• Exposure (E): how often the driving situation occurs.
• Controllability (C): how likely the driver or others can avoid harm.

The combination gives an Automotive Safety Integrity Level (ASIL) from A to D, or QM when standard quality management is enough. A steering or braking function failing unexpectedly at speed typically lands at the high end of the scale.

From safety goals to requirements

Each hazard leads to a safety goal, which is refined into functional and then technical safety requirements, allocated to hardware and software. The higher the ASIL, the more rigorous the methods required — for example stronger verification, independence between design and review, and quantitative hardware metrics.

The V-model in practice

ISO 26262 follows a V-shaped development process: requirements and design go down the left side; integration, verification and validation go up the right side. Traceability links every requirement to the tests that prove it. Supporting processes — configuration management, change management, tool qualification and safety assessment — run throughout.

ISO 26262 and ADAS

Advanced driver assistance and automated driving add a difficulty: a system can be fault-free and still behave unsafely because its sensors or algorithms misread a situation. That gap is covered by ISO 21448 (SOTIF, safety of the intended functionality). Connected vehicles also need ISO/SAE 21434 for cybersecurity. Engineers working on software-defined vehicles usually apply all three together.

Where to start

Functional safety is a career in itself. Our autonomous, ADAS and software-defined vehicle programmes cover these standards with real case studies. You may also like our article on detect-and-avoid systems for drones, where similar safety thinking applies in the air.