Overview
ISO 14230-4:2000 specifies the requirements for the Keyword Protocol 2000 (KWP2000) data link and connected vehicle and scan tool when used to comply with on-board diagnostic (OBD) requirements for emission-related test data. This part focuses solely on the OBD-related constraints and behaviours of the KWP2000 protocol; complete protocol specifications are contained in ISO 14230 parts 1–3 and ISO 14229. The standard ensures consistent, interoperable communication between vehicles and diagnostic tools for emission testing.
Key benefits:
- Ensures interoperability between vehicle ECUs and scan tools for emission diagnostics
- Defines constrained message and timing behaviour for reliable emission test data
- Helps manufacturers and tool developers maintain OBD compliance
Key Topics
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Message structure: The header shall always consist of three bytes. An optional length byte shall not be used. Data length is limited to 7 bytes for compatibility with ISO 15031-5. Format bits A1A0 distinguish request (11) and response (10) messages and determine addressing mode.
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Addressing: Functional address 33H is used as the target address for messages sent to the vehicle. Responses target the source address included in the request; response source addresses are the physical addresses of ECUs.
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Timing: Only the normal timing parameter set with default values shall be used for both vehicle and scan tool. Timing exceptions described in ISO 14230-2 are not permitted.
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Start/initialisation: ECUs shall support either 5 baud initialisation or fast initialisation; scan tools shall support both. Accepted keywords include 2025, 2027, 2029 and 2031, but only the functionality of keyword 2025 (3-byte header, no length byte, normal timing) shall be used. For 5 baud init, the 5 baud address is 33H and subsequent communication occurs at 10 400 baud.
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Services and control: The vehicle shall support StopCommunication. The AccessTimingParameter service shall not be supported by the scan tool. The TesterPresent service must be supported by the vehicle to maintain an active session (with mandatory responses and use within P3).
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Negative responses: Modules must reply with a positive or negative response when no transmission error occurred. Allowed negative response codes include 10, 11, 12, 21, 22, 78. Responses containing code 78 must be sent within P2 and followed by a final positive or different negative response.
Applications
- OBD emission testing and verification
- Diagnostic scan tool development and certification
- Vehicle ECU firmware and diagnostic interface design
- Regulatory compliance testing and service workshop diagnostics
Related Standards
This part of ISO 14230 provides the OBD-specific constraints and operational rules for KWP2000 to ensure consistent, reliable exchange of emission-related diagnostic data between vehicles and external diagnostic equipment.