ISO 26262-4:2011

INTERNATIONAL ISO
STANDARD 26262-4
First edition
2011-11-15

Road vehicles — Functional safety —
Part 4:
Product development at the system level
Véhicules routiers — Sécurité fonctionnelle —
Partie 4: Développement du produit au niveau du système




Reference number
ISO 26262-4:2011(E)
©
ISO 2011

---------------------- Page: 1 ----------------------
ISO 26262-4:2011(E)

COPYRIGHT PROTECTED DOCUMENT


©  ISO 2011
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56  CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland

ii © ISO 2011 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 26262-4:2011(E)
Contents Page
Foreword . v
Introduction . vi
1  Scope . 1
2  Normative references . 2
3  Terms, definitions and abbreviated terms . 2
4  Requirements for compliance . 2
4.1  General requirements . 2
4.2  Interpretations of tables . 3
4.3  ASIL-dependent requirements and recommendations . 3
5  Initiation of product development at the system level . 3
5.1  Objectives . 3
5.2  General . 4
5.3  Inputs to this clause . 6
5.4  Requirements and recommendations . 6
5.5  Work products . 6
6  Specification of the technical safety requirements . 7
6.1  Objectives . 7
6.2  General . 7
6.3  Inputs to this clause . 7
6.4  Requirements and recommendations . 7
6.5  Work products . 10
7  System design . 10
7.1  Objectives . 10
7.2  General . 11
7.3  Inputs to this clause . 11
7.4  Requirements and recommendation . 11
7.5  Work products . 16
8  Item integration and testing . 16
8.1  Objectives . 16
8.2  General . 16
8.3  Inputs to this clause . 16
8.4  Requirements and recommendation . 17
8.5  Work products . 25
9  Safety validation . 25
9.1  Objectives . 25
9.2  General . 25
9.3  Inputs to this clause . 26
9.4  Requirements and recommendation . 26
9.5  Work products . 27
10  Functional safety assessment . 28
10.1  Objectives . 28
10.2  General . 28
10.3  Inputs to this clause . 28
10.4  Requirements and recommendation . 28
10.5  Work products . 28
11  Release for production . 28
© ISO 2011 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO 26262-4:2011(E)
11.1  Objectives .28
11.2  General .29
11.3  Inputs to this clause .29
11.4  Requirements and recommendations .29
11.5  Work products .30
Annex A (informative) Overview and document flow of product development at the system level .31
Annex B (informative) Example contents of hardware-software interface .33
Bibliography .36

iv © ISO 2011 – All rights reserved

---------------------- Page: 4 ----------------------
ISO 26262-4:2011(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 26262-4 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 3,
Electrical and electronic equipment.
ISO 26262 consists of the following parts, under the general title Road vehicles — Functional safety:
 Part 1: Vocabulary
 Part 2: Management of functional safety
 Part 3: Concept phase
 Part 4: Product development at the system level
 Part 5: Product development at the hardware level
 Part 6: Product development at the software level
 Part 7: Production and operation
 Part 8: Supporting processes
 Part 9: Automotive Safety Integrity Level (ASIL)-oriented and safety-oriented analyses
 Part 10: Guideline on ISO 26262
© ISO 2011 – All rights reserved v

---------------------- Page: 5 ----------------------
ISO 26262-4:2011(E)
Introduction
ISO 26262 is the adaptation of IEC 61508 to comply with needs specific to the application sector of electrical
and/or electronic (E/E) systems within road vehicles.
This adaptation applies to all activities during the safety lifecycle of safety-related systems comprised of
electrical, electronic and software components.
Safety is one of the key issues of future automobile development. New functionalities not only in areas such
as driver assistance, propulsion, in vehicle dynamics control and active and passive safety systems
increasingly touch the domain of system safety engineering. Development and integration of these
functionalities will strengthen the need for safe system development processes and the need to provide
evidence that all reasonable system safety objectives are satisfied.
With the trend of increasing technological complexity, software content and mechatronic implementation, there
are increasing risks from systematic failures and random hardware failures. ISO 26262 includes guidance to
avoid these risks by providing appropriate requirements and processes.
System safety is achieved through a number of safety measures, which are implemented in a variety of
technologies (e.g. mechanical, hydraulic, pneumatic, electrical, electronic, programmable electronic) and
applied at the various levels of the development process. Although ISO 26262 is concerned with functional
safety of E/E systems, it provides a framework within which safety-related systems based on other
technologies can be considered. ISO 26262:
a) provides an automotive safety lifecycle (management, development, production, operation, service,
decommissioning) and supports tailoring the necessary activities during these lifecycle phases;
b) provides an automotive-specific risk-based approach to determine integrity levels [Automotive Safety
Integrity Levels (ASIL)];
c) uses ASILs to specify applicable requirements of ISO 26262 so as to avoid unreasonable residual risk;
d) provides requirements for validation and confirmation measures to ensure a sufficient and acceptable
level of safety being achieved;
e) provides requirements for relations with suppliers.
Functional safety is influenced by the development process (including such activities as requirements
specification, design, implementation, integration, verification, validation and configuration), the production
and service processes and by the management processes.
Safety issues are intertwined with common function-oriented and quality-oriented development activities and
work products. ISO 26262 addresses the safety-related aspects of development activities and work products.
Figure 1 shows the overall structure of this edition of ISO 26262. ISO 26262 is based upon a V-model as a
reference process model for the different phases of product development. Within the figure:
 the shaded “V”s represent the interconnection between ISO 26262-3, ISO 26262-4, ISO 26262-5,
ISO 26262-6 and ISO 26262-7;
 the specific clauses are indicated in the following manner: “m-n”, where “m” represents the number of the
particular part and “n” indicates the number of the clause within that part.
EXAMPLE “2-6” represents Clause 6 of ISO 26262-2.
vi © ISO 2011 – All rights reserved

---------------------- Page: 6 ----------------------
ISO 26262-4:2011(E)

Figure 1 — Overview of ISO 26262

© ISO 2011 – All rights reserved vii

1. Vocabulary
2. Management of functional safety
2-6 Safety management during the concept phase 2-7 Safety management after the item´s release
2-5 Overall safety management
and the product development for production
4. Product development at the system level
3. Concept phase 7. Production and operation
4-5 Initiation of product
4-11 Release for production
3-5 Item definition 7-5 Production
development at the system level
4-10 Functional safety assessment
7-6 Operation, service
3-6 Initiation of the safety lifecycle
4-6 Specification of the technical
(maintenance and repair), and
safety requirements
decommissioning
4-9 Safety validation
3-7 Hazard analysis and risk
assessment
4-7 System design 4-8 Item integration and testing
3-8 Functional safety
concept
5. Product development at the 6. Product development at the
hardware level software level
5-5 Initiation of product 6-5 Initiation of product
development at the hardware level
development at the software level
5-6 Specification of hardware
safety requirements
5-7 Hardware design 6-7 Software architectural design
5-8 Evaluation of the hardware 6-8 Software unit design and
architectural metrics implementation
5-9 Evaluation of the safety goal
6-9 Software unit testing
violations due to random hardware
failures
6-10 Software integration and
5-10 Hardware integration and
testing
testing
6-11 Verification of software safety
requirements
8. Supporting processes
8-5 Interfaces within distributed developments 8-10 Documentation
8-6 Specification and management of safety requirements 8-11 Confidence in the use of software tools
8-7 Configuration management 8-12 Qualification of software components
8-8 Change management 8-13 Qualification of hardware components
8-9 Verification 8-14 Proven in use argument
9. ASIL-oriented and safety-oriented analyses
9-5 Requirements decomposition with respect to ASIL tailoring 9-7 Analysis of dependent failures
9-6 Criteria for coexistence of elements 9-8 Safety analyses
10. Guideline on ISO 26262

---------------------- Page: 7 ----------------------
INTERNATIONAL STANDARD ISO 26262-4:2011(E)

Road vehicles — Functional safety —
Part 4:
Product development at the system level
1 Scope
ISO 26262 is intended to be applied to safety-related systems that include one or more electrical and/or
electronic (E/E) systems and that are installed in series production passenger cars with a maximum gross
vehicle mass up to 3 500 kg. ISO 26262 does not address unique E/E systems in special purpose vehicles
such as vehicles designed for drivers with disabilities.
Systems and their components released for production, or systems and their components already under
development prior to the publication date of ISO 26262, are exempted from the scope. For further
development or alterations based on systems and their components released for production prior to the
publication of ISO 26262, only the modifications will be developed in accordance with ISO 26262.
ISO 26262 addresses possible hazards caused by malfunctioning behaviour of E/E safety-related systems,
including interaction of these systems. It does not address hazards related to electric shock, fire, smoke, heat,
radiation, toxicity, flammability, reactivity, corrosion, release of energy and similar hazards, unless directly
caused by malfunctioning behaviour of E/E safety-related systems.
ISO 26262 does not address the nominal performance of E/E systems, even if dedicated functional
performance standards exist for these systems (e.g. active and passive safety systems, brake systems,
Adaptive Cruise Control).
This part of ISO 26262 specifies the requirements for product development at the system level for automotive
applications, including the following:
 requirements for the initiation of product development at the system level,
 specification of the technical safety requirements,
 the technical safety concept,
 system design,
 item integration and testing,
 safety validation,
 functional safety assessment, and
 product release.
© ISO 2011 – All rights reserved 1

---------------------- Page: 8 ----------------------
ISO 26262-4:2011(E)
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 26262-1:2011, Road vehicles — Functional safety — Part 1: Vocabulary
ISO 26262-2:2011, Road vehicles — Functional safety — Part 2: Management of functional safety
ISO 26262-3:2011, Road vehicles — Functional safety — Part 3: Concept phase
ISO 26262-5:2011, Road vehicles — Functional safety — Part 5: Product development at the hardware level
ISO 26262-6:2011, Road vehicles — Functional safety — Part 6: Product development at the software level
ISO 26262-7:2011, Road vehicles — Functional safety — Part 7: Production and operation
ISO 26262-8:2011, Road vehicles — Functional safety — Part 8: Supporting processes
ISO 26262-9:2011, Road vehicles — Functional safety — Part 9: Automotive Safety Integrity Level (ASIL)-
oriented and safety-oriented analyses
3 Terms, definitions and abbreviated terms
For the purposes of this document, the terms, definitions and abbreviated terms given in ISO 26262-1:2011
apply.
4 Requirements for compliance
4.1 General requirements
When claiming compliance with ISO 26262, each requirement shall be complied with, unless one of the
following applies:
a) tailoring of the safety activities in accordance with ISO 26262-2 has been planned and shows that the
requirement does not apply, or
b) a rationale is available that the non-compliance is acceptable and the rationale has been assessed in
accordance with ISO 26262-2.
Information marked as a “NOTE” or “EXAMPLE” is only for guidance in understanding, or for clarification of
the associated requirement, and shall not be interpreted as a requirement itself or as complete or exhaustive.
The results of safety activities are given as work products. “Prerequisites” are information which shall be
available as work products of a previous phase. Given that certain requirements of a clause are
ASIL-dependent or may be tailored, certain work products may not be needed as prerequisites.
“Further supporting information” is information that can be considered, but which in some cases is not required
by ISO 26262 as a work product of a previous phase and which may be made available by external sources
that are different from the persons or organizations responsible for the functional safety activities.
2 © ISO 2011 – All rights reserved

---------------------- Page: 9 ----------------------
ISO 26262-4:2011(E)
4.2 Interpretations of tables
Tables are normative or informative depending on their context. The different methods listed in a table
contribute to the level of confidence in achieving compliance with the corresponding requirement. Each
method in a table is either
a) a consecutive entry (marked by a sequence number in the leftmost column, e.g. 1, 2, 3), or
b) an alternative entry (marked by a number followed by a letter in the leftmost column, e.g. 2a, 2b, 2c).
For consecutive entries, all methods shall be applied as recommended in accordance with the ASIL. If
methods other than those listed are to be applied, a rationale shall be given that these fulfil the corresponding
requirement.
For alternative entries, an appropriate combination of methods shall be applied in accordance with the ASIL
indicated, independent of whether they are listed in the table or not. If methods are listed with different
degrees of recommendation for an ASIL, the methods with the higher recommendation should be preferred. A
rationale shall be given that the selected combination of methods complies with the corresponding
requirement.
NOTE A rationale based on the methods listed in the table is sufficient. However, this does not imply a bias for or
against methods not listed in the table.
For each method, the degree of recommendation to use the corresponding method depends on the ASIL and
is categorized as follows:
 “++” indicates that the method is highly recommended for the identified ASIL;
 “+” indicates that the method is recommended for the identified ASIL;
 “o” indicates that the method has no recommendation for or against its usage for the identified ASIL.
4.3 ASIL-dependent requirements and recommendations
The requirements or recommendations of each subclause shall be complied with for ASIL A, B, C and D, if not
stated otherwise. These requirements and recommendations refer to the ASIL of the safety goal. If ASIL
decomposition has been performed at an earlier stage of development, in accordance with ISO 26262-9:2011,
Clause 5, the ASIL resulting from the decomposition shall be complied with.
If an ASIL is given in parentheses in ISO 26262, the corresponding subclause shall be considered as a
recommendation rather than a requirement for this ASIL. This has no link with the parenthesis notation related
to ASIL decomposition.
5 Initiation of product development at the system level
5.1 Objectives
The objective of the initiation of the product development at the system level is to determine and plan the
functional safety activities during the individual subphases of system development. This also includes the
necessary supporting processes described in ISO 26262-8.
This planning of system-level safety activities will be included in the safety plan.
© ISO 2011 – All rights reserved 3

---------------------- Page: 10 ----------------------
ISO 26262-4:2011(E)
5.2 15BGeneral
The necessary activities during the development of a system are given in Figure 2. After the initiation of
product development and the specification of the technical safety requirements, the system design is
performed. During system design the system architecture is established, the technical safety requirements are
allocated to hardware and software, and, if applicable, on other technologies. In addition, the technical safety
requirements are refined and requirements arising from the system architecture are added, including the
hardware-software interface (HSI). Depending on the complexity of the architecture, the requirements for
subsystems can be derived iteratively. After their development, the hardware and software elements are
integrated and tested to form an item that is then integrated into a vehicle. Once integrated at the vehicle level,
safety validation is performed to provide evidence of functional safety with respect to the safety goals.
ISO 26262-5 and ISO 26262-6 describe the development requirements for hardware and software. This part
of ISO 26262 applies to both the development of systems and subsystems. Figure 3 is an example of a
system with multiple levels of integration, illustrating the application of this part of ISO 26262, ISO 26262-5
and ISO 26262-6.
NOTE 1 Table A.1 provides an overview of objectives, prerequisites and work products of the particular subphases of
product development at the system level.
Part 4: Product development: system level
Initiation of product development
4-5
at the system level
Specification of the technical safety
4-6
requirements
System design
4-7
Part 5: Product development: hardware level Part 6: Product development: software level
Item integration and testing
4-8
Safety validation
4-9
Functional safety assessment
4-10
Release for production
4-11

NOTE 2 Within the figure, the specific clauses of each part of ISO 26262 are indicated in the following manner: “m-n”,
where “m” represents the number of the part and “n” indicates the number of the clause, e.g. “4-5” represents Clause 5 of
ISO 26262-4.
Figure 2 — Reference phase model for the development of a safety-related item
4 © ISO 2011 – All rights reserved

---------------------- Page: 11 ----------------------
ISO 26262-4:2011(E)

NOTE Within the figure, the specific clauses of each part of ISO 26262 are indicated in the following manner: “m-n”,
where “m” represents the number of the part and “n” indicates the number of the clause, e.g. “4-5” represents Clause 5 of
ISO 26262-4.
Figure 3 — Example of a product development at the system level
© ISO 2011 – All rights reserved 5

System
Initiation of product
4-5
development at the system level
Specification of the technical
4-6
safety requirements
4-7 System design
Sub-system A Sub-system B
Specification of the technical
4-6
safety requirements
4-7 System design
Specification of the technical
4-6
safety requirements
4-7 System design
Sub-system B1 Sub-system B2
Specification of the technical Specification of the technical
4-6 4-6
safety requirements safety requirements
4-7 System design 4-7 System design
Part 5: Product Part 6: Product Part 5: Product Part 6: Product Part 5: Product Part 6: Product
development: development: software development at the development at the development: development:
hardware level level hardware level software level hardware level software level
4-8.4.2 Hardw are - softw are integration and testing 4-8.4.2 Hardw are – softw are integration and testing 4-8.4.2 Hardw are – softw are integration and testing
4-8.4.3 System integration and testing
4-8.4.3 System integration and testing
4-8.4.4 Vehicle integration and testing

---------------------- Page: 12 ----------------------
ISO 26262-4:2011(E)
5.3 Inputs to this clause
5.3.1 Prerequisites
The following information shall be available:
 project plan (refined) in accordance with ISO 26262-2:2011, 6.5.2;
 safety plan in accordance with ISO 26262-3:2011, 6.5.2;
 functional safety assessment plan in accordance with ISO 26262-2:2011, 6.5.4; and
 functional safety concept in accordance with ISO 26262-3:2011, 8.5.1.
5.3.2 Further supporting information
The following information can be considered:
 preliminary architectural assumptions (from external source); and
 item definition (see ISO 26262-3:2011, 5.5).
5.4 Requirements and recommendations
5.4.1 The safety activities for the product development at the system level shall be planned including
determination of appropriate methods and measures during design and integration.
NOTE The results of planning of the verification activities during design in accordance with 6.4.6 (Verification and
validation) and 7.4.8 (Verification of system design) are part of the safety plan while the planning of item integration and
testing in accordance with 8.4.2 (hardware/software), 8.4.3 (element integration) and 8.4.4 (item integration) is
represented in a separate item integration and testing plan in accordance with requirement 8.4.1.3.
5.4.2 The validation activities shall be planned.
5.4.3 The functional safety assessment activities for the product development at the system level shall b
...