Keyword Protocol 2000
Keyword Protocol 2000 (KWP2000) is a communications protocol designed for on-board vehicle diagnostics (OBD), facilitating the exchange of diagnostic data between external tools and electronic control units (ECUs) in automotive systems.[1] Standardized under ISO 14230-4:2000 for its data link layer and vehicle interface, KWP2000 specifies requirements for serial data communication over K-Line networks, supporting initialization, timing management, and diagnostic services.[2] It operates across multiple OSI layers, from physical transmission (e.g., K-Line per ISO 14230-2) to application-level diagnostics, with adaptations for Controller Area Network (CAN) via ISO 15765.[3] Developed in the mid-1990s by a task force involving major automakers such as BMW and Volkswagen, KWP2000 was first released as a recommended practice in October 1997, evolving from earlier protocols like ISO 9141 to address growing needs for ECU diagnostics in multi-processor vehicle architectures.[1] Key features include flexible initialization methods—such as the slow 5-baud handshake for address synchronization or fast initialization at up to 10,400 baud—and message structures comprising a header (up to 4 bytes for addressing and length), data payload (up to 255 bytes), and an 8-bit checksum for error detection.[4] Essential services encompass StartCommunication (to initiate sessions with priority levels), StopCommunication (to terminate links), AccessTimingParameters (to adjust response times like P2 defaults at 25 ms), and optional data transmission functions for reading/clearing diagnostic trouble codes, input/output control, and ECU programming.[1][3] Primarily deployed in European and Asian vehicles from the late 1990s through the 2000s—particularly in brands like Suzuki, Honda, and Kawasaki—KWP2000 supports both single-wire K-Line and dual-wire L-Line buses, with gateway compatibility for broader networks like CAN or SAE J1850.[4] While it enabled efficient fault detection, real-time data access, and software flashing in legacy systems, its limitations in handling large data packets (up to 4 GB via CAN extensions) have led to gradual replacement by the Unified Diagnostic Services (UDS) protocol under ISO 14229, though KWP2000 remains prevalent in heavy-duty diesel applications and older models.[3][4]Overview
Definition and Purpose
The Keyword Protocol 2000 (KWP2000) is a bidirectional serial communication protocol designed for on-board vehicle diagnostics (OBD), enabling standardized data exchange between external diagnostic tools and vehicle electronic control units (ECUs).[5] It forms the basis for diagnostic interactions in automotive systems, supporting request-response messaging to facilitate vehicle health monitoring and maintenance.[3] The primary purpose of KWP2000 is to allow diagnostic tools to access ECU-stored data, read and clear diagnostic trouble codes (DTCs) that indicate faults, and execute real-time actuator tests to verify component functionality.[6] This protocol ensures efficient troubleshooting by providing structured access to vehicle parameters and status information, reducing diagnostic time and improving accuracy in identifying issues such as engine malfunctions or emissions irregularities.[7] KWP2000 is standardized for deployment over both controller area network (CAN) and K-line physical layers, with widespread adoption in European and Asian vehicles starting from the late 1990s to meet regulatory requirements.[3] Its key benefits include enhanced fault diagnosis capabilities, support for ECU reconfiguration during service, and essential compliance with emissions standards such as European On-Board Diagnostics (EOBD), which mandates standardized OBD functionality for environmental monitoring.[6] KWP2000 is defined within the ISO 14230 standard series, which outlines its layered implementation for diagnostic services.[2]OSI Model Mapping
The Keyword Protocol 2000 (KWP2000), standardized as ISO 14230, structures its diagnostic communication according to the OSI reference model (ISO/IEC 7498-1), dividing responsibilities across relevant layers while leaving some higher layers undefined or handled externally.[8] Specifically, the protocol defines the physical layer (Layer 1) in ISO 14230-1, which supports serial interfaces such as K-line for bidirectional communication.[9] The data link layer (Layer 2) is detailed in ISO 14230-2, managing framing, error detection, and basic addressing mechanisms.[10] For network (Layer 3) and transport (Layer 4) functionalities, KWP2000 provides partial implementation, primarily through segmentation and reassembly of messages exceeding single-frame limits, especially in CAN-based deployments using ISO 15765-2 (ISO-TP).[4] This enables handling of larger diagnostic payloads up to several kilobytes by breaking them into network protocol data units (N-PDUs) for transmission over the underlying bus.[4] Layers 5 (session) and 6 (presentation) are not explicitly defined in the ISO 14230 suite, with session establishment and maintenance handled through application layer services such as start and stop communication, coordinated by the data link layer's timing parameters to ensure reliable diagnostic sessions.[8] These timing requirements, including minimum and maximum delays for responses (e.g., 25-50 ms for normal addressing), span Layers 1-4 to coordinate message flow without dedicated higher-layer protocols.[10] The application layer (Layer 7) is the core of KWP2000's diagnostic capabilities, as specified in ISO 14230-3, where services like read data by identifier and routine control are implemented.[8] Overall, Layers 1-4 form the foundational core for KWP2000's operation in vehicle networks, with higher-layer abstractions (Layers 5-7) largely managed by external diagnostic tools or gateways rather than the protocol itself.[4] Addressing in KWP2000 operates within this layered framework, distinguishing between physical addressing—which targets specific electronic control units (ECUs) via unique identifiers at the data link layer—and functional addressing, which broadcasts requests to multiple ECUs fulfilling a common role, routed through network/transport segmentation when needed.[1] This dual approach ensures efficient layered communication, with physical addressing used for direct ECU interactions and functional addressing for network-wide diagnostics, all constrained by the protocol's timing and error controls across the lower layers.[10]Physical Layers
K-Line Implementation
The K-Line serves as a single-wire bidirectional serial interface for the physical layer in Keyword Protocol 2000 (KWP2000), standardized under ISO 9141-2 for vehicle diagnostics communication.[11] It enables asynchronous serial transmission between diagnostic testers and electronic control units (ECUs) via the SAE J1962 OBD-II connector, where the K-Line connects to pin 7.[12] An optional L-Line on pin 15 supports slow initialization by providing a unidirectional wake-up signal from the tester to the ECU, though many systems operate solely on the K-Line.[13] This setup aligns with ISO 14230-1, which defines the physical layer for KWP2000 over K-Line. Signaling on the K-Line uses asynchronous serial protocol with voltage levels up to 12 V, starting at a low 5 baud rate for initialization to ensure reliable ECU wake-up and protocol detection.[11] Post-initialization, the baud rate increases to a maximum of 10.4 kbps for data exchange, supporting UART-based communication tailored to automotive environments. The protocol employs idle-high signaling, where the line is pulled high when inactive, and data bits are transmitted with start and stop bits for frame synchronization.[11] Initialization begins with a keyword search sequence: the tester transmits the address byte 0x33 at 5 baud over approximately 2 seconds, prompting the ECU to respond with the 0x55 keyword pattern if compatible, followed by key bytes (such as 0x08 0x08 or 0x94 0x94) to confirm the protocol.[11] For KWP2000 fast initialization, a 50 ms wake-up pattern at 10.4 kbps precedes a StartCommunication request (e.g., 0xC1 0x33 0xF1 0x81 0x66), with the ECU replying via a positive response.[11] This low-cost implementation suits older ECUs in European and Asian vehicles due to minimal hardware needs, but it is limited by the 10.4 kbps speed ceiling, making it slower than multi-wire alternatives for high-volume data transfer.[11]CAN Implementation
The CAN implementation of Keyword Protocol 2000 (KWP2000) integrates with the ISO 15765 standards to enable diagnostic communication over Controller Area Network (CAN) buses in vehicles, where ISO 15765-2 specifies the transport layer and ISO 15765-4 defines the application layer for road vehicle diagnostics. This setup allows KWP2000 services to operate atop the CAN physical and data link layers, facilitating high-speed, multi-node networking for electronic control unit (ECU) interactions without the need for dedicated wakeup sequences required in serial implementations.[4] The CAN bus employs differential signaling between the CAN_H (high) and CAN_L (low) lines, connected to pins 6 and 14 on the standard 16-pin OBD-II diagnostic connector, ensuring robust noise immunity in automotive environments. Common baud rates for diagnostic applications under ISO 15765 range from 250 kbps to 500 kbps, with support for up to 1 Mbps in high-speed variants, enabling efficient data transfer across vehicle networks.[14][15][16] Addressing in KWP2000 over CAN utilizes either 11-bit standard identifiers for simpler networks or 29-bit extended identifiers to target specific ECUs with greater precision and priority arbitration during bus contention. These identifiers form part of the CAN frame structure, allowing functional or physical addressing of diagnostic requests and responses.[15][17] The transport protocol follows ISO 15765-2 (ISO-TP), supporting single-frame messages for payloads up to 8 bytes, which suffice for basic KWP2000 services like read data by identifier. For longer messages, multi-frame segmentation assembles consecutive CAN frames into complete diagnostic packets, with flow control mechanisms to manage transmission rates and prevent bus overload.[17][18] Adoption of KWP2000 over CAN became prevalent in vehicles starting around 2003, coinciding with European mandates for CAN-based EOBD systems and the phase-in of high-speed networks in North American models, enhancing diagnostic capabilities for complex, multi-ECU architectures.[19][20]Data Link Layer
Framing and Addressing
The data link layer in Keyword Protocol 2000 (KWP2000) structures diagnostic messages into frames to ensure reliable transmission between a tester and electronic control units (ECUs). A frame begins with a start of frame (SOF) marked by the physical layer's start bit, followed by an optional length byte indicating the total number of data bytes (1 to 255). The header then includes a format byte that specifies addressing mode and short message length (up to 63 bytes if no length byte is present), along with optional target and source address bytes. The data field starts with the service identifier (SID), which identifies the requested diagnostic service, followed by variable parameters specific to that service; the frame ends with an 8-bit checksum byte (sum of all preceding bytes modulo 256) and an end of frame (EOF) via the stop bit.[4][1] Addressing in KWP2000 operates in two modes to support targeted or group communications: physical addressing directs messages to a specific ECU using unique identifier bytes (e.g., derived from ISO 9141 5-baud initialization), while functional addressing broadcasts to all capable ECUs for parallel processing, with the format byte's upper bits set to 11 for requests and 10 for responses to avoid collisions. In functional mode, the tester typically uses address 0x33 for initiating requests, enabling synchronization during communication startup. These mechanisms are transmitted over physical layers such as K-line or CAN for serial or bus-based delivery.[4][1][21] Message lengths in KWP2000 are constrained to 1-255 bytes for the data field (SID plus parameters). This fixed-length approach simplifies parsing while accommodating variable diagnostic content. Timing parameters govern frame transmission, including inter-byte delays (P1: 0-20 ms) to allow ECU processing between bytes and response timeouts (P2: 25-50 ms in normal mode, extendable to 1000 ms), which can be negotiated post-initialization to optimize data link performance.[4][1]Error Detection and Control
In the Keyword Protocol 2000 (KWP2000), error detection at the data link layer primarily relies on a single-byte checksum appended to each message frame to verify data integrity. The checksum is calculated as the sum of all bytes in the frame excluding the checksum itself, taken modulo 256, ensuring that the receiving electronic control unit (ECU) can detect transmission errors such as bit flips or byte losses.[10] This mechanism is positioned at the end of the frame structure, immediately following the data bytes, and the ECU discards any message with an invalid checksum without generating a response.[10] Error responses are handled through negative responses (NR) issued by the ECU when a diagnostic request cannot be processed, formatted as a service identifier (SID) of 0x7F followed by the original request SID and a specific error code. Common error codes include 0x21 for "busy-repeatRequest," indicating the ECU is temporarily unable to respond and the tester should retry after a delay, and 0x22 for "conditionsNotCorrect," signaling that prerequisites such as vehicle state or session mode are not met.[22] These responses enable the tester to diagnose and adapt to issues without full session termination.[22] Flow control in KWP2000 is achieved through timing parameters and periodic messaging rather than explicit acknowledgments in the basic mode, with the tester sending a "Tester Present" message (SID 0x3E) at regular intervals to maintain the diagnostic session and prevent ECU timeout.[22] The positive response to this service is SID 0x7E, confirming session continuity, while the absence of ACK/NAK in standard exchanges relies on the ECU's P2max timer for response expectations.[22] Recovery procedures following errors emphasize reinitialization, where the tester resends the StartCommunication keyword (SID 0x81) after a wait period of W5 (typically 300 ms) to reestablish the link, or retries up to three times on timeout or invalid responses before escalating to full session reset.[10] This approach minimizes downtime while ensuring robust fault tolerance across K-line and CAN implementations.[10]Application Layer
Diagnostic Services
The Keyword Protocol 2000 (KWP2000) employs Service Identifiers (SIDs) in the hexadecimal range 0x01 to 0x3E to specify diagnostic requests at the application layer, enabling communication between a tester and electronic control units (ECUs) in vehicles.[23] These SIDs facilitate standardized interactions for fault diagnosis and vehicle maintenance, with responses structured to confirm success or indicate errors. Positive responses modify the request SID by adding 0x40 (e.g., 0x53 for a 0x13 request), while negative responses use SID 0x7F followed by the original SID and a Negative Response Code (NRC) such as 0x11 for service not supported or 0x33 for security access denied.[23] This dual-response mechanism ensures reliable error handling across various diagnostic scenarios.[24] Key diagnostic services in KWP2000 include reading diagnostic trouble codes (DTCs) via SID 0x13, which retrieves stored fault codes from the ECU memory to identify vehicle issues.[23] Clearing DTCs employs SID 0x14 to reset fault codes and associated data, often requiring confirmation before execution to prevent accidental data loss.[23] SID 0x21 (read data by identifier) allows the tester to query specific data elements, such as sensor values or status flags, using local or common identifiers for targeted information retrieval.[23] Input/output control via SID 0x2F enables manipulation of ECU-controlled devices, like actuators or indicators, supporting functions such as override testing during repairs.[23] Routine control with SID 0x31 initiates, stops, or queries predefined ECU routines, including self-diagnostic tests or calibration procedures.[23] Security access is managed through SID 0x27, which implements a challenge-response authentication using a seed-key mechanism to protect sensitive operations. The tester requests a random seed from the ECU, derives a key via a proprietary algorithm, and submits it for verification; successful authentication grants access to restricted services, with failed attempts triggering delays or locks to prevent brute-force attacks.[23] ECU identification via SID 0x09 retrieves essential vehicle-specific data, including the Vehicle Identification Number (VIN) and calibration identifiers, aiding in part matching and software verification during service.[24] KWP2000 supports multiple session types to adapt to different diagnostic needs, starting with the default session for basic operations like tester presence confirmation without an explicit entry request. Extended sessions and programming sessions are initiated using SID 0x10 (start diagnostic session) with manufacturer-specific parameters, such as 0x02 for extended diagnostics enabling advanced queries or 0x03 for programming mode allowing firmware updates. These sessions layer additional capabilities atop the default while maintaining backward compatibility for standard tools.[23]Data Formats and Responses
In the Keyword Protocol 2000 (KWP2000), as defined in the application layer of ISO 14230-3, requests are structured as a single-byte Service Identifier (SID) followed by an optional sub-function byte and service-specific parameters, such as a Parameter Identifier (PID) or Data Identifier (DID) for data retrieval operations.[25] The SID identifies the diagnostic service, while parameters like PIDs or DIDs specify the data to be accessed, ensuring precise communication between the diagnostic tool and the electronic control unit (ECU).[22] Responses in KWP2000 follow standardized formats to indicate success or failure. A positive response consists of the original SID logically ORed with0x40, followed by the sub-function (if applicable) and the requested data, confirming successful execution of the service.[25] For instance, a request with SID 0x10 (Start Diagnostic Session) yields a positive response starting with 0x50. In contrast, a negative response begins with 0x7F, followed by the original SID and a Negative Response Code (NRC) indicating the error type, such as 0x11 for service not supported; this structure allows the diagnostic tool to handle faults without ambiguity.[22]
Data Identifiers (DIDs) are two-byte hexadecimal codes used to access specific ECU parameters, providing a modular way to query vehicle status; DIDs and their scaling are typically manufacturer-specific.[25][22]
For responses exceeding the single-frame limit—particularly eight bytes on CAN implementations—KWP2000 employs multi-frame handling through concatenation rules, where data is segmented using services like TransferData and reassembled by the receiver.[25] This mechanism supports payloads up to 255 bytes by issuing multiple frames, with the first and last frames flagged accordingly to maintain integrity during transmission.[22]
All data in KWP2000 is encoded as hexadecimal bytes, with physical values derived via scaling factors specified per DID.[25] This encoding ensures compact representation while allowing straightforward conversion to engineering units.[22]