SAE J1978-2-2025 第二代协议OBD-II扫描工具

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SURFACE VEHICLE

RECOMMENDED PRACTICE

J1978™-2

DEC2025

Issued 2024-12

Revised 2025-12

OBD-II Scan Tool - Second Generation Protocols

RATIONALE

This document has been revised to include further DoIP content, editorial revisions, and clarifications.

FOREWORD

On-board diagnostic (OBD) regulations require passenger cars and light- and medium-duty trucks to support the

communication of a minimum set of diagnostic information with off-board “generic” test equipment (e.g., OBD II scan tool).

This document describes the minimum capabilities that must be supported by an OBD-II scan tool (e.g., handheld scan

tools, PC-based diagnostic computers, etc.) that are intended to communicate with an OBD-compliant vehicle to retrieve

the OBD information. SAE J1978 was originally developed to meet U.S. OBD requirements for 1996 and later model year

vehicles. SAE J1978-2 represents the second document in the SAE J1978 OBD-II scan tool family of recommended

practices. The document has been created to represent industry advancement of allowed second generation protocols for

OBD-II “generic” scan tool use. Also, as part of the SAE J1978 document family, the separate first document, SAE J1978-1,

contains recommended practice information on allowed first generation OBD data links.

INTRODUCTION

SAE J1978-2 defines a set of user functions necessary for a scan tool that supports the diagnostic scan tool use case of

emission-related and zero emissions-related subsystems that utilize on-board diagnostic (OBD) capability on second

generation protocols. Additionally, this document offers recommended practices for key topics that the scan tool must

support, such as required communication protocols, scan tool power management, applicable diagnostic connector, and

guidance on user interface text. This document strives to share, within the scope of legislated emissions-related and zero

emissions-related OBD, the description of the interaction between a vehicle’s OBD system and an external OBD-II “generic”

scan tool.

Acknowledging early OBD-II “generic” scan tool document development, it is important to note that SAE J1978-2 is one of

several SAE documents necessary for understanding the diagnostic scan tool use case. For full comprehension of this use

case, there are applicable ISO documents that must be considered.

SAE INTERNATIONAL J1978™-2 DEC2025 Page 2 of 62

TABLE OF CONTENTS

1. SCOPE .......................................................................................................................................................... 4

2. REFERENCES .............................................................................................................................................. 4

2.1 Applicable Documents .................................................................................................................................. 4

2.1.1 SAE Publications ........................................................................................................................................... 4

2.1.2 ISO Publications ............................................................................................................................................ 5

3. DEFINITIONS ............................................................................................................................................... 6

4. ABBREVIATIONS ......................................................................................................................................... 6

5. SYMBOLS ..................................................................................................................................................... 7

6. CONVENTIONS ............................................................................................................................................ 7

7. DOCUMENT OVERVIEW ............................................................................................................................. 8

8. REQUIRED FUNCTIONS OF THE OBD-II SCAN TOOL ............................................................................. 9

9. COMMUNICATION PROTOCOLS ............................................................................................................... 9

10. CONNECTIONS TO THE VEHICLE ............................................................................................................. 9

11. AUTOMATIC DETERMINATION OF COMMUNICATION INTERFACE ...................................................... 9

12. NETWORK ACCESS - SECOND GENERATION PROTOCOLS ................................................................. 9

12.1 Multiple Tester Communication .................................................................................................................... 9

12.1.1 General ......................................................................................................................................................... 9

12.1.2 Behavior of an OBD-II Scan Tool .................................................................................................................. 9

12.2 Handling of No Response from the Vehicle ................................................................................................ 10

12.3 Handling of Multiple Responses from the Vehicle ...................................................................................... 10

12.4 Message Structure ...................................................................................................................................... 10

12.5 Diagnostic Trouble Codes Monitoring ......................................................................................................... 10

12.5.1 SAE J2012 DTC Format 0x04 Descriptive Information .............................................................................. 10

12.5.2 SAE J1939 DTC Format 0x02 Descriptive Information .............................................................................. 11

12.6 Obtain and Display Current Data/Freeze Frame, Test Results, and Vehicle Identification Data ............... 11

12.7 Code Clearing ............................................................................................................................................. 12

12.8 On-Board Diagnostic Evaluations ............................................................................................................... 12

12.8.1 Completed On-Board System I/M Monitor Readiness Tests ...................................................................... 12

12.8.2 On-Board System I/M Monitor Readiness Tests - Support Status ............................................................. 12

12.8.3 On-Board System I/M Monitor Readiness Tests - Ready Status................................................................ 13

12.8.4 Malfunction Indicator Lamp - Status and Control ........................................................................................ 13

13. USER INTERFACE ..................................................................................................................................... 13

13.1 Display......................................................................................................................................................... 13

13.2 User Input .................................................................................................................................................... 13

14. POWER REQUIREMENTS......................................................................................................................... 14

15. ELECTROMAGNETIC COMPATIBILITY (EMC) ........................................................................................ 14

16. CONFORMANCE TESTING ....................................................................................................................... 14

17. NOTES ........................................................................................................................................................ 14

17.1 Revision Indicator ........................................................................................................................................ 14

APPENDIX A RECOMMENDED EXTERNAL TEST EQUIPMENT COMMON USER INTERFACE DISPLAYS ............. 15

APPENDIX B METHOD TO DETERMINE DTC SUPPORT OF DTCEXTENDEDDATARECORDS ............................... 61

SAE INTERNATIONAL J1978™-2 DEC2025 Page 3 of 62

Figure 1 OBD II scan tool diagnostic services document reference (per OSI model) ................................................ 8

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标签： #OBD-II

摘要：

SAE J1978-2-2025 是全球汽车诊断领域的重要标准，专门规范第二代协议OBD-II扫描工具的性能与功能要求。该标准在原有J1978基础上进行重大升级，针对新一代车载诊断系统（包括CAN、DoIP及未来扩展协议）定义了更严格的通信兼容性、数据解析精度、故障码读取与清除能力、实时参数流展示以及排放相关监测功能。它要求扫描工具必须支持SAE J1978-2规定的服务模式，确保与所有符合OBD-II法规的轻型车辆实现无缝交互，同时强化了安全访问、软件更新和网络安全机制。通过遵循这一最新标准，

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