Overview
ISO 9141-3:1998 - "Road vehicles - Diagnostic systems - Part 3: Verification of the communication between vehicle and OBD II scan tool" defines recommended test methods, procedures and parameter values to verify communication between a vehicle and an OBD II scan tool that use the ISO 9141-2 protocol. It focuses on interoperability testing of the complete bus implementation, not on single ECU modules or subparts of an ISO 9141-2 network. The standard tests message structure, initialization sequencing and physical-layer limits to confirm correct behaviour of vehicles and scan tools.
Key topics and requirements
- Three defined test procedures
- Message structure test - verifies correct response to valid and invalid messages, including logical responses, checksum and length handling.
- Initialization test - checks initialization sequence timing and correct handling of initialization errors.
- Physical layer test - verifies transmit/receive electrical parameters fall within ISO 9141-2 limits.
- Test equipment and set-up
- Network Access Device (NAD) to simulate and monitor vehicle or scan tool behaviour (annex D lists minimum NAD requirements). NAD accuracy (ΔNAD) is accounted for when assessing results.
- Power supply (PS): capable of 5 A in 0–20 V range; test set-ups often use PS = 13.5 V ± 0.5 V.
- Digital Storage Oscilloscope (DSO): minimum 50 MHz, 10 MΩ input, ≤20 pF capacitance.
- Ancillary items: DUT (device under test), personal computer for logging, cabling per annex A.
- Test parameters and messages
- Uses specified timing parameters (P, P1, P2, etc.), reference test messages and timing tables (annexes B and C).
- Tests assess correct retry behaviour (e.g., retransmit after checksum error), timing ranges and message formats.
- Scope limits
- Not intended to verify requirements outside ISO 9141-2 (explicitly excludes SAE J1962, SAE J1978, ISO 15031‑5 and expanded diagnostic protocols).
- Not applicable as a test for an individual module or partial network.
Applications and users
- Who uses it
- Vehicle manufacturers (OEMs) for bus-level compliance testing.
- OBD II scan tool and diagnostic tool manufacturers for interoperability validation.
- Independent test labs and certification bodies performing protocol verification.
- Aftermarket diagnostic service providers validating tool/vehicle compatibility.
- Practical uses
- Pre‑production and validation to ensure ISO 9141-2 communication works end‑to‑end.
- Troubleshooting tool/vehicle interoperability issues at the bus level.
- Formal verification in compliance programs that require documented test procedures and parameters.
Related standards
- ISO 9141-2:1994 - CARB requirements for interchange of digital information (protocol specification).
- ISO 9141:1989 - General diagnostic information interchange requirements.
- Referenced but not verified by this part: SAE J1962, SAE J1978, ISO 15031-5.
Keywords: ISO 9141-3, OBD II, diagnostic systems, vehicle communication, ISO 9141-2, message structure test, initialization test, physical layer test, NAD, DSO, scan tool interoperability.