ISO 26262 and ISO/SAE 21434 address different automotive risks: ISO 26262 deals with hazards caused by malfunctioning behaviour in safety-related electrical and electronic (E/E) systems, while ISO/SAE 21434 sets out cybersecurity risk-management engineering across a vehicle E/E system’s lifecycle. They are complementary, not substitutes; using one does not automatically satisfy the other.
What does functional safety mean in automotive?
Functional safety concerns the risk that a safety-related E/E system behaves incorrectly or fails to perform its intended function, creating a hazard. For example, an unintended output or a failed control function may have safety consequences. ISO 26262 provides a framework for addressing such risks in covered systems, including interactions between them.
The scope is not every possible vehicle hazard, nor is it a measure of whether an E/E system performs well under normal conditions. ISO says ISO 26262 addresses hazards caused by malfunctioning behaviour and explicitly excludes nominal E/E performance. Its framework is intended to integrate functional-safety activities into an organization’s development framework, using both technical product requirements and process requirements. ISO 26262-1:2018
What does ISO/SAE 21434 cover?
ISO/SAE 21434:2021 establishes engineering requirements for cybersecurity risk management in road vehicles. Its lifecycle scope includes concept, development, production, operation, maintenance and decommissioning of E/E systems. The standard focuses on cybersecurity engineering and risk-management processes rather than prescribing a particular security technology or tool. ISO describes it as technology-agnostic. ISO/SAE 21434:2021
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Cybersecurity risk is distinct from functional-safety risk, but the two can intersect. A cyber threat may affect a safety-related function; conversely, a system malfunction can create a safety hazard without being caused by a cyberattack. Teams therefore need to coordinate relevant safety and cybersecurity work while assessing each risk under the appropriate discipline.
ISO 26262 and ISO/SAE 21434 compared
| Comparison | ISO 26262 | ISO/SAE 21434 |
|---|---|---|
| Primary risk domain | Functional-safety hazards caused by malfunctioning behaviour of safety-related E/E systems. | Cybersecurity risks affecting road-vehicle E/E systems. |
| Main focus | Functional-safety management, lifecycle activities, product development and supporting processes. | Cybersecurity engineering and risk-management processes throughout the E/E lifecycle. |
| Technology prescriptions | A functional-safety framework with requirements; it is not a statement that normal system performance is in scope. | Technology-agnostic: it does not prescribe specific technologies or solutions. |
| How they relate | Provides the functional-safety perspective when malfunctioning behaviour can create hazards. | Provides the cybersecurity perspective; it complements functional-safety engineering where cyber risks could affect safety-related systems. |
ISO’s own explanation is direct: “ISO 26262 focuses on functional safety, while ISO/SAE 21434 addresses cybersecurity.” ISO also says the standards are often implemented together. That does not make their objectives interchangeable, or mean that conformance to one demonstrates conformance to the other. ISO/SAE 21434:2021
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How UN Regulation No. 155 fits in
UN Regulation No. 155 (R155) is a vehicle type-approval regulation concerning cybersecurity and cybersecurity management systems (CSMS). It is not another name for ISO/SAE 21434: one is a regulation governing approval in relevant markets and vehicle contexts; the other is an engineering standard. Applicability depends on the market, vehicle category and approval requirements, so R155 should not be described as a universal rule for every vehicle.
The 2025/5 consolidated text covers L, M, N and O category vehicles fitted with at least one electronic control unit. It defines a CSMS as “a systematic risk-based approach defining organisational processes, responsibilities and governance to treat risk associated with cyber threats to vehicles and protect them from cyber-attacks.” EU Official Journal consolidated text of UN Regulation No. 155
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The EU’s consolidated text is marked in force and incorporates Supplement 3, effective 10 January 2025; it notes that the authentic, legally binding texts are the UN/ECE texts. The UN Treaty Collection records R155’s entry into force on 22 January 2021 and amendments through 2025. Applying ISO/SAE 21434 does not by itself confer R155 vehicle approval. UN Treaty Collection: UN Regulation No. 155
Published editions and revision status
As of 8 October 2026, ISO lists ISO 26262:2018 as the published second edition. The series package comprises ten parts. ISO lists a third edition of Part 2 in the enquiry phase as a draft intended to replace ISO 26262-2:2018; it is not a published replacement. ISO 26262-1:2018 ISO 26262 series package ISO 26262-2 revision
ISO lists ISO/SAE 21434:2021 as the published first edition, dated August 2021. A second-edition work item is under development, with a draft prepared and an indication that it will replace the 2021 edition. The work item is not itself a published replacement. Check ISO’s live publication pages for status when selecting a standard for a project, as work-item stages can change. ISO/SAE 21434:2021 ISO/SAE 21434 second-edition work item
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the standards do not guarantee
These standards provide engineering frameworks and requirements; citing or applying them is not a guarantee that a vehicle is safe or secure. ISO specifically cautions that applying ISO/SAE 21434 alone does not make vehicles secure. Outcomes depend on how organizations implement the relevant lifecycle activities and address the risks within their scope. ISO/SAE 21434:2021
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