Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
SAE J1699-2-2024: Essential Test Cases for OBD-II Scan Tools and I/M Test Equipment
The SAE J1699-2-2024 standard provides a comprehensive set of test cases for verifying compliance of OBD-II scan tools and Inspection/Maintenance (I/M) test equipment. Covering mechanical dimensions, electrical characteristics, and protocol evaluation, this recommended practice has been stabilized as of December 2024, as its definitions are not applicable to current technology. Nevertheless, its content remains relevant for legacy diagnostics and foundational understanding of conformance testing.
⚠️ Stabilized Status: This standard is no longer actively maintained but provides a critical reference for testing equipment used with older vehicle systems and for understanding OBD-II compliance foundations.
Overview of SAE J1699-2-2024 and Its Test Coverage
This standard organizes tests into three core evaluation areas: mechanical, electrical, and protocol. For each OBD-II communication protocol (CAN/ISO 15765-4, ISO 14230-4, ISO 9141-2, SAE J1850 VPW, SAE J1850 PWM), the standard specifies detailed test procedures, expected behaviors, and pass/fail criteria. The table below summarizes the main test categories and representative examples.
| Evaluation Area | Key Tests | Applicable Protocols |
|---|---|---|
| Mechanical | SAE J1962 connector dimensions, cable length measurement | All (connector common to all OBD-II) |
| Electrical | Current draw, network termination, capacitance verification | CAN, ISO 14230-4, ISO 9141-2, SAE J1850 VPW/PWM |
| Protocol | Initialization sequences, timing, message handling, error detection | ISO 15765-4, ISO 14230-4, ISO 9141-2, SAE J1850 VPW, SAE J1850 PWM |
Protocol tests cover a wide range: from verifying bit timing and 5-baud initialization for ISO 9141-2 and ISO 14230-4, to CAN protocol initialization with multiple ECUs, error frames, and negative response codes. For example, Section 8 of the standard includes tests for BS and STMIN parameters, initialization with delayed acknowledgements, and handling of NRC=$21.
Key Engineering Specifications and Design Insights
The standard emphasizes the importance of correct network termination and capacitance for reliable communication. For CAN (ISO 15765-4), termination resistors must be properly measured; for ISO 14230-4 and ISO 9141-2, the K-line and L-line capacitance must meet specified limits. These requirements directly affect signal integrity and protocol timing — common pitfalls that can lead to intermittent faults or startup failures.
🛠️ Engineering Design Insight: Conformance to SAE J1699-2 ensures that a scan tool can correctly interface across multiple vehicle protocols by validating physical-layer attributes and initialization handshakes. Pay special attention to the network termination and capacitance tests for each protocol, as these are often overlooked but essential for robust diagnostics communication.
🔍 Common Mistake Alert: One frequent failure is improper network termination for CAN — either missing or incorrect resistor values can prevent bus communication entirely. Always verify the resistor scheme against the 120 Ω nominal requirement for high‑speed CAN.
Another critical area is the OBD-II initialization sequence. The standard defines distinct patterns for each protocol, including 5‑baud handshakes (ISO 9141-2, ISO 14230‑4) and CAN arbitration with 11‑bit or 29‑bit identifiers. Tests such as “Verify Protocol Initialization with No Acknowledgement” or “with Error Frame Detected” help validate that the scan tool properly handles abnormal states and timeout conditions, ensuring resilience in real‑world service bays.
Frequently Asked Questions about SAE J1699-2-2024
- What is the purpose of SAE J1699-2-2024?
It defines test cases to verify that OBD-II scan tools and I/M test equipment meet mechanical, electrical, and protocol requirements across all common OBD-II communication standards. - Which protocols are covered by the standard?
The standard covers CAN (ISO 15765-4), ISO 14230-4, ISO 9141-2, SAE J1850 VPW, and SAE J1850 PWM — the full set of legislated OBD-II protocols. - What are the main mechanical tests for the SAE J1962 connector?
Tests include verifying pin dimensions, connector shape, and cable length to ensure physical compatibility with all vehicles. - Why was the standard stabilized?
The SAE committees determined that the definitions are no longer applicable to current technology. However, the document remains a key reference for legacy systems and for understanding test methodology.
By following the test cases outlined in SAE J1699-2-2024, engineers can design scan tools and I/M equipment that correctly handle protocol initialization, electrical constraints, and the physical interface — delivering reliable diagnostic performance for both modern and older vehicles.
