Diagnostic Standard OBDonUDS – SAE J1979-2 | Softing (2024)

FAQs

What is the SAE J1979 standard? ›

SAE J1979/ISO 15031-5 specifies diagnostic services and functionally addressed request/response messages required to be supported by motor vehicles and external test equipment for diagnostic purposes which pertain to motor vehicle emission-related data.

SAE J1979 OBD-II | Emission related Diagnostic Protocol. SAE J1979 (On-Board Diagnostics-II), is a standard used to monitor and report the status of various vehicle systems, including emissions-related components and detect malfunctions or faults that may affect the vehicle's performance and emissions.

OBD-II diagnostic connector

The OBD-II specification provides for a standardized hardware interface — the female 16-pin (2x8) J1962 connector, where type A is used for 12-volt vehicles and type B for 24-volt vehicles.

The OBD-II protocol supports multiple signal protocols, which determine how data is transferred between the vehicle and the diagnostic tool. The most commonly used protocols are ISO 9141-2, KWP2000, J1850 VPW, J1850 PWM, and ISO 15765 CAN (Controller Area Network).

SAE originated in the early 1900s as the Society of Automobile Engineers but soon became the Society of Automotive Engineers, a move that reflected its growing influence beyond the automobile.

The SAE J1979-3 standard introduces on-board diagnostics (OBD) also for electric vehicles / Zero Emission Vehicles (ZEVs) and Plug-in Hybrid Electric Vehicles (PHEVs). The SAE J1979 family of standards describe in detail how OBD data can be easily read from vehicles using an external diagnostic device ("scan tool").

OBD-II codes, or trouble codes, tell you specifically what's wrong with your car – from the transmission to the ignition, to brakes and airbags.

OBD-II codes alert you when your car is having issues – everything from airbags to brakes. The most common place to access them is through the OBD-II port under your vehicle's steering column. They're generally standard in issue but can be manufacturer-specific.

What cars are OBD-II compliant? ›

1996 or newer model year vehicle sold in the United States

United States legislation requires all cars and light trucks model year (MY) 1996 and newer to be OBD2 compliant. More information is available on the EPA's website.

In most cases, communication issues can be caused by various reasons including: ignition-key position, connector-voltage issues, incorrect communication protocol, hung ECM, missing or bad data, and OEM-updated ECM software that is unknown to the scan tool. Below we explain some of them with more details.

Does my car have OBD II? All 1996 and newer model year gasoline and alternate fuel passenger cars and trucks are required to have OBD II systems. All 1997 and newer model year diesel fueled passenger cars and trucks are also required to meet the OBD II requirements.

From 1994 onwards, EPA regulations require presence of OBD systems in light duty vehicles (LDV) and light duty trucks (LDT). OBD-II, an enhanced capability OBD standard computer system is mandatory for vehicle models from 1996 onwards.

1996: OBD2 made mandatory in USA for cars/light trucks. 2001: Required in EU for gasoline cars. 2003: Required in EU also for diesel cars (EOBD) 2005: OBD2 was required in US for medium duty vehicles.

Similarly to J1979, J1939 is a set of SAE International standards that outline how ECMs communicate through the CAN bus for heavy-duty vehicles. If you think of the CAN as a method of communication, like a telephone, both J1939 and J1979 use the same process but speak a different language.

SAE standards are internationally recognized as a trusted collection of scientific data to globally optimize the processes, practices, and products that advance technology in the Aerospace industry and are vital to ensure safety, quality, and reliability.

SAE number, code for specifying the viscosity of lubricating oil, established by the U.S. Society of Automotive Engineers. The numbers for crankcase lubricants range from 5 to 50, for transmission and axle lubricants they range from 75 to 250; the lower the number, the more readily the oil flows.

SAE Correction

SAE, unlike uncorrected or STD, also uses a mechanical efficiency (friction) modifier in the correction factor, which assumes an 85-percent mechanical efficiency or a 15-percent differential in engine power due to frictional loss, which is fairly accurate in a standard all-motor application.