ISO 14230-1:2012

Overview

ISO 14230-1:2012 specifies the physical layer for Diagnostic Communication over K‑Line (DoK‑Line) used in road vehicles. Based on ISO 9141 and ISO 9141‑2, this part extends the physical-layer rules to support vehicles with either 12 V d.c. or 24 V d.c. electrical systems. It defines line configurations, signal levels, timing constraints, wiring and capacitance limits, and minimum electrical and functional requirements for both vehicle ECUs and external test equipment (diagnostic tools).

Key topics and technical requirements

• Physical-layer basis: Builds on ISO 9141/9141‑2 and maps to the OSI model (layer 1) for DoK‑Line diagnostic services.
• K‑ and L‑line configurations: Supports one‑wire (K only) or two‑wire (K and L) topologies. K-line is bidirectional for normal communications; L-line is unidirectional and used only during initialization.
• Signal voltage thresholds: Logic levels are specified as percentages of the vehicle battery voltage (Vb):
  • Logic “0” (transmit): < 20% Vb; receiver threshold ~30% Vb.
  • Logic “1” (transmit): > 80% Vb; receiver threshold ~70% Vb.
• Coding and timing: NRZ (non‑return‑to‑zero) coding is used. Slope times and bit timing are constrained (slope times must be less than a defined fraction of the bit time).
• Capacitance limits: Limits on input and wiring capacitance ensure reliable comms - for 12 V systems CECU + COBW ≤ 7.2 nF and CTE ≤ 2 nF; for 24 V systems the comparable limits apply (values in standard).
• External test equipment requirements: Minimum functional support for initialization and protocol per ISO 14230‑2; electrical operating ranges specified (e.g., correct operation over nominal battery ranges and working temperature 0–50 °C).
• Vehicle wiring and ECU behavior: Rules to avoid unintended initialization, manage multiple ECUs on a shared bus, and prevent collisions when lines are used for other purposes.

Applications and practical value

• Implementing a robust, interoperable physical interface for vehicle diagnostics over K‑Line.
• Ensuring diagnostic tools (scan tools, service testers) and ECUs interoperate reliably across 12 V and 24 V vehicle platforms.
• Guiding wiring design, connector usage and EMI considerations for diagnostic interfaces.
• Supporting emissions‑related on‑board diagnostics and manufacturer diagnostic services that sit above the physical layer.

Who uses this standard

• Automotive OEM electrical and communication engineers
• ECU and module suppliers
• Diagnostic tool and tester manufacturers
• Vehicle service equipment designers and test labs
• Standards and compliance engineers working on OBD/WWH‑OBD implementations

Related standards

• ISO 9141 / ISO 9141‑2 (foundation for K‑Line physical layer)
• ISO 14230‑2 (data link layer) and ISO 14230‑4 (data link requirements)
• ISO 14229 (UDS application layer)
• ISO 15031 series (emissions diagnostics) and ISO 7637 (electrical disturbance testing)

Keywords: ISO 14230‑1, DoK‑Line, K‑Line, diagnostic communication, physical layer, vehicle diagnostics, ECU, external test equipment, 12 V, 24 V.