What ISO 26262 and ASIL levels mean for developers

ISO 26262 is a functional safety standard for automotive electronics and software systems. It defines a structured safety lifecycle aligned with the V-model, spanning everything from initial requirements to final validation and maintenance.

The V-model is a development framework where each design phase is paired with a corresponding test phase. This structure makes it easier to trace safety requirements from early specifications through to system verification.

Key concepts in ISO 26262

  • Automotive Safety Integrity Level (ASIL) ranks the safety criticality of components on a scale from A (lowest) to D (highest). For example, ASIL A might apply to a dashboard indicator failure, while ASIL D applies to a brake system malfunction.

  • Hazard Analysis and Risk Assessment (HARA) identifies potential hazards and evaluates their risks to define the required safety goals and ASIL levels.

  • Safety mechanisms include techniques such as real-time fault detection, redundancy, and fallback modes like fail-safe and fail-operational behavior.

Note In practice, many OEMs default to ASIL D for systems with any potential for passenger harm, even if the statistical likelihood of failure is low.

Apply ISO 26262 to real-world systems

ISO 26262 applies to many safety-critical vehicle systems:

  • Autonomous driving systems must respond safely to sensor errors (such as LiDAR, radar, or camera faults). Functional safety ensures the vehicle can enter a safe state and avoid unsafe decisions.

  • Powertrain control systems monitor throttle and braking inputs. Safety mechanisms such as redundancy, plausibility checks, and overrides prevent unintended acceleration or loss of braking function.

  • Battery management systems (BMS) protect electric vehicle batteries from overheating, overcharging, or deep discharge. Built-in safety functions monitor temperature, balance voltage, and isolate faulty circuits to prevent thermal runaway.

These systems require dedicated hardware and software architectures that enforce functional safety guarantees. One common solution is the safety island, which is an isolated compute domain used to run safety-critical control logic independently from the main system.

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