Diagnostic standards and protocols

Below is an overview of the main standards and protocols used in automotive diagnostics, grouped by their purpose and relationships.

SAE J1850

Overview: One of the early standards for automotive diagnostic buses, widely used in American vehicles before the advent of CAN. Defines the VPW (Variable Pulse Width) and PWM (Pulse Width Modulation) protocols.
SAE J2178-1: Data link layer for SAE J1850.
SAE J2178-2, SAE J2178-3, SAE J2178-4: Application/presentation layers for SAE J1850.
Physical layer: 10.4 Kbps VPW, 41.6 Kbps PWM.

KWP2000 (ISO 14230)

Overview: Keyword Protocol 2000. Defines the data link requirements for diagnostics, allowing an external tester to communicate with an ECU. Includes specifications for byte encoding and hexadecimal values for diagnostic services (ISO 14229), requests and responses.
ISO 14230-3: Application layer for KWP2000.
ISO 14230-2: Data link layer for KWP2000.
ISO 14230-1: Physical layer for KWP2000 (K-Line).
SAE J2818 (KLine): Covers the application, presentation, session, transport, network and data link layers.
SAE J3054 (TP1.6): Data link layer for CAN 11bit. Used by the VAG group as the TP1.6 protocol.

KW 1281

Overview: A protocol primarily used by the VAG group (Volkswagen, Audi, Skoda, Seat) for diagnostics of older vehicle models. Runs over K-Line or CAN.
SAE J2818 (KLine): Covers the application, presentation, session, transport, network and data link layers.
SAE J3054/TP1.6 (CAN): Data link layer for CAN 11bit. Used by the VAG group as the TP1.6 protocol.

TP2.0

Overview: Transport Protocol 2.0. A transport layer protocol developed by VAG to run over the CAN bus, a predecessor of UDS.
SAE J2819: Covers the application, presentation, session, transport, network and data link layers.

GM UART

Overview: A diagnostic protocol used by General Motors, often running over K-Line.
SAE J2740: Covers the application, presentation, session, transport, network and data link layers.
K-Line: Physical layer.

ISO 15765 (DoCAN)

Overview: Diagnostics over CAN. A standard that describes how diagnostic messages are transmitted over the CAN bus. It is the foundation for UDS and OBD-II over CAN.
ISO 15765-2: Transport and network layers.
ISO 15765-3: Application and session layers.
ISO 11898-1: Data link layer (CAN).
SAE J2284-1, SAE J2284-2, SAE J2284-3, SAE J2284-4: Physical layer.

OBDII (On-Board Diagnostics II)

Overview: A standardized vehicle self-diagnostic system, mandatory for all passenger cars sold in the USA since 1996 and in Europe since 2001. Provides access to emissions-related data.
SAE J1979 / ISO 15031-5: Application layer, defines diagnostic modes and parameters.
ISO 15765-4: Covers the transport, network, data link and physical layers for OBD-II over CAN.
SAE J2178-1: Data link layer for SAE J1850.
10.4 Kbps VPW, 41.6 Kbps PWM, ISO 9141-2 (K-Line), ISO 14230-1, CAN: Physical layer.

UDS (ISO 14229)

Overview: Unified Diagnostic Services. A modern protocol used by most automakers for dealer diagnostics and ECU programming. Can run over various transport protocols (CAN, Ethernet, K-Line).
ISO 14229-1: Application and presentation layers.
ISO 14229-2: Session layer.
ISO 15765-2: Transport and network layers (for UDS over CAN).
ISO 20794-3: Transport and network layers (for UDS over Ethernet).
ISO 20794-4: Data link layer (for UDS over Ethernet).
ISO 11898-1: Data link layer (CAN).
SAE J1962 / ISO 15031-3: Connectors (OBD-II).

DoIP (ISO 13400)

Overview: Diagnostics over Internet Protocol. Enables ECU diagnostics and programming over Ethernet, which is particularly relevant for modern vehicles with high-speed networks.
ISO 13400-2: Transport and network layers.
ISO 13400-3: Data link layer.
IEEE 802.3: Physical layer (Ethernet).
ISO 13400-4: Connectors.

WWH-OBD (ISO 27145)

Overview: World-Wide Harmonized On-Board Diagnostics. An extension of OBD-II for heavy-duty vehicles and beyond, aimed at unifying diagnostic data.
ISO 27145-2: Presentation layer.
ISO 27145-3: Application layer.
ISO 14229-2: Session layer.
ISO 13400-2: Transport and network layers.
ISO 13400-3: Data link layer.
IEEE 802.3: Physical layer (Ethernet).
ISO 13400-4: Connectors.

GM LAN (GMW 3110)

Overview: A protocol used by General Motors for communication over the CAN bus, often using OSEK-COM.
GMW 3110: Application layer.
OSEK-COM (USDT/UUDT Protocol): Transport and network layers.
ISO 11898-1: Data link layer (CAN).
GMW 3122 (DW-CAN), GMW 3089 (SW-CAN): Physical layer.
GMW 3173: Connectors.

The table below shows the main standards and protocols used in automotive diagnostics and how they map to the layers of the OSI model.

	7 application	6 presentation	5 session	4 transport	3 network	2 data link	1 physical	0 connectors
SAE J1850		SAE J2178‑2 SAE J2178‑3 SAE J2178‑4				SAE J2178‑1	10.4 Kbps VPW
SAE J1850		SAE J2178‑2 SAE J2178‑3 SAE J2178‑4				SAE J2178‑1	41.6 Kbps PWM
KWP2000	ISO 14230‑3					ISO 14230‑2	ISO 14230‑1
KWP2000	ISO 14230‑3					SAE J3054	CAN 11bit
KW 1281				SAE J2818	SAE J2818	SAE J2818	SAE J2818
KW 1281						SAE J3054	CAN 11bit
TP2.0				SAE J2819	SAE J2819	SAE J2819	SAE J2819
GM UART				SAE J2740	SAE J2740	SAE J2740	K‑line
ISO 15765 (DoCAN)	ISO 15765‑3		ISO 15765‑3	ISO 15765‑2	ISO 15765‑2	ISO 11898‑1	SAE J2284‑1 SAE J2284‑2 SAE J2284‑3 SAE J2284‑4
OBDII	SAE J1979 ISO 15031‑5				ISO 15765‑4	ISO 15765‑4	ISO 15765‑4
						SAE J2178‑1	10.4 Kbps VPW
						SAE J2178‑1	41.6 Kbps PWM
						ISO 9141‑2	ISO 9141‑2
						ISO 14230‑2	ISO 14230‑1
UDS	ISO 14229‑1	ISO 14229‑1	ISO 14229‑2	ISO 15765‑2	ISO 15765‑2	ISO 11898‑1		SAE J1962 ISO 15031‑3
				ISO 20794‑3	ISO 20794‑3	ISO 20794‑4
						SAE J3054
UDSonCAN	ISO 14229‑3	ISO 14229‑3	ISO 14229‑2			ISO 11898‑1
UDSonCAN	ISO 14229‑3	ISO 14229‑3	ISO 14229‑2	ISO 20794‑3	ISO 20794‑3	ISO 20794‑4
UDSonCXPI	ISO 14229‑8	ISO 14229‑8	ISO 14229‑8	ISO 20794‑3	ISO 20794‑3	ISO 20794‑4
DoIP	ISO 14229‑1		ISO 14229‑2	ISO 13400‑2	ISO 13400‑2	ISO 13400‑3	IEEE 802.3	ISO 13400‑4
WWH‑OBD	ISO 27145‑3	ISO 27145‑2	ISO 14229‑2	ISO 13400‑2	ISO 13400‑2	ISO 13400‑3	IEEE 802.3	ISO 13400‑4
GM LAN	GMW 3110				OSEK‑COM (USDT/UUDT Protocol)	ISO 11898‑1	GMW 3122 (DW‑CAN) GMW 3089 (SW‑CAN)	GMW 3173