As a car owner or automotive technician, you’ve likely heard of OBD2. But to truly tap into the power of On-Board Diagnostics II (OBD2), you need the right tool: the Obd2 Diagnostic Cable. This seemingly simple cable is your gateway to understanding your vehicle’s health, performance, and potential issues.
In this in-depth guide, we’ll explore everything you need to know about the OBD2 diagnostic cable. We’ll demystify the OBD2 protocol, explain the cable’s crucial role, and show you how it connects you to a wealth of vehicle data.
Consider this your ultimate resource for understanding the OBD2 diagnostic cable and its vital function in modern automotive diagnostics.
You can also watch our OBD2 intro video above – or get the PDF
In this article
Author: Martin Falch (updated January 2025)
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What is OBD2 and Why Do You Need a Diagnostic Cable?
OBD2 is essentially your car’s internal doctor, a standardized system that monitors and reports on your vehicle’s various systems. Since the mid-1990s, OBD2 has been a standard feature in almost all cars, providing access to diagnostic trouble codes (DTCs) and real-time data. This access point is made possible through the OBD2 diagnostic cable, which connects your vehicle’s OBD2 port to a diagnostic tool.
Think of the malfunction indicator light (MIL), often called the “check engine light,” on your dashboard. When this light illuminates, it’s your car signaling a problem. To understand what’s wrong, a mechanic uses an OBD2 scanner. This scanner, equipped with an OBD2 diagnostic cable, plugs into the 16-pin OBD2 connector, typically found under the dashboard near the steering wheel.
The OBD2 diagnostic cable facilitates communication between the scanner and your car’s computer. The scanner sends ‘OBD2 requests’ through the cable, and the car responds with ‘OBD2 responses’. These responses can include vital information like speed, fuel level, and, most importantly, Diagnostic Trouble Codes (DTCs). This real-time data flow, enabled by the OBD2 diagnostic cable, is crucial for efficient and accurate troubleshooting.
The malfunction indicator light (MIL) is a key indicator that prompts the use of an OBD2 diagnostic cable for vehicle diagnostics.
Is Your Car OBD2 Compatible? And Cable Considerations
The good news is, if you own a relatively modern car, it almost certainly supports OBD2. Most non-electric cars manufactured in recent decades are OBD2 compliant and often utilize the CAN bus protocol for communication. However, older vehicles, even if they have a 16-pin connector resembling an OBD2 port, might not actually support the OBD2 protocol. It’s important to verify compatibility, especially when choosing an OBD2 diagnostic cable.
A simple way to check for OBD2 compliance is to consider the vehicle’s origin and year of purchase. Generally:
Compliance timelines help determine if your vehicle is OBD2 compatible, influencing the type of OBD2 diagnostic cable needed.
When selecting an OBD2 diagnostic cable, ensure it is compatible with your vehicle’s OBD2 port type (Type A or Type B – discussed later) and the communication protocols your car uses. A mismatch can prevent proper data transfer and hinder diagnostics.
A Brief History of OBD2 and its Cable Evolution
The story of OBD2 begins in California, driven by the California Air Resources Board (CARB)’s need to regulate vehicle emissions. In 1991, CARB mandated OBD systems in all new cars sold in California for emission control. This marked the genesis of standardized vehicle diagnostics.
The Society of Automotive Engineers (SAE) played a crucial role in standardizing OBD, leading to the OBD2 standard. SAE standardized DTCs and the OBD connector itself (SAE J1962), ensuring compatibility across different car manufacturers. This standardization is what allows a single OBD2 diagnostic cable to work with a wide range of vehicles.
The OBD2 standard was progressively implemented across the US and Europe:
- 1996: OBD2 became mandatory in the USA for cars and light trucks.
- 2001: The EU required OBD2 for gasoline cars.
- 2003: The EU extended the requirement to diesel cars (EOBD).
- 2005: OBD2 was mandated in the US for medium-duty vehicles.
- 2008: US vehicles were required to use ISO 15765-4 (CAN) as the foundation for OBD2 communication.
- 2010: OBD2 became compulsory for heavy-duty vehicles in the US.
The historical focus of OBD2 on emission control highlights the initial purpose behind the technology accessible via the OBD2 diagnostic cable.
The timeline of OBD2 adoption shows the increasing importance of standardized diagnostics and the role of the OBD2 diagnostic cable in accessing vehicle data.
Future trends in OBD anticipate more advanced diagnostics and remote capabilities, potentially impacting the future of the OBD2 diagnostic cable and its functionalities.
The Future of OBD2 and the Diagnostic Cable in a Connected World
OBD2 is firmly established, but its future is evolving. While initially designed for emission control, OBD2’s capabilities are being stretched and adapted in the age of connected cars.
Interestingly, electric vehicles (EVs), primarily focused on electric powertrains and not emissions in the traditional sense, are not always required to support OBD2 in the same way. In practice, many modern EVs don’t support standard OBD2 requests. Instead, they often utilize OEM-specific UDS communication protocols. This makes accessing data from EVs more complex, often requiring reverse engineering efforts, as seen in case studies for brands like Tesla, Hyundai/Kia, Nissan, and VW/Skoda. This shift in EV diagnostics may necessitate specialized diagnostic cables and tools beyond standard OBD2.
To address the limitations of current OBD2 implementations, newer standards like WWH-OBD (World Wide Harmonized OBD) and OBDonUDS (OBD on UDS) are emerging. These aim to enhance OBD communication by using the UDS protocol as a foundation, promising richer data and streamlined diagnostics. These advancements might influence the design and capabilities of future OBD2 diagnostic cables, potentially requiring them to handle more complex protocols.
The rise of connected cars also raises questions about the future of manual OBD2 checks. OBD3 concepts are being explored, envisioning telematics integration. OBD3 could involve incorporating a radio transponder in vehicles to wirelessly transmit Vehicle Identification Numbers (VINs) and DTCs to a central server for automated emission checks and diagnostics. Devices like the CANedge2 WiFi CAN logger and CANedge3 3G/4G CAN logger already demonstrate the feasibility of wireless OBD2 data transfer. While convenient, such advancements also spark debates about data privacy and surveillance. The OBD2 diagnostic cable in this scenario might become less about direct physical connection for basic diagnostics and more about specialized connections for advanced data access or system reprogramming.
Another significant trend is the automotive industry’s push to control access to vehicle data. Historically, OBD2 has been used by third parties for various services, creating a data-driven economy around vehicle information. However, some manufacturers are proposing to restrict OBD2 functionality during driving, centralizing data collection and potentially limiting third-party access. This move, argued in terms of security and hacking risks, is also seen by many as a commercial strategy to control valuable automotive data. This potential shift could significantly impact the aftermarket OBD2 services and the role of the OBD2 diagnostic cable in those services.
The increasing complexity of vehicle systems, especially in EVs, might lead to changes in how the OBD2 diagnostic cable is used and what data it can access.
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OBD2 Standards and the Diagnostic Cable Specifications
OBD2 operates as a higher-layer protocol, like a language, while CAN bus is the communication method, similar to a phone line. This is analogous to other CAN-based protocols like J1939, CANopen, and NMEA 2000. OBD2 standards define various aspects, including the OBD2 connector, lower-layer protocols, and OBD2 parameter IDs (PIDs). The OBD2 diagnostic cable is built to comply with these connector and protocol standards to ensure proper communication.
These standards can be visualized using the 7-layer OSI model, with SAE and ISO standards covering different layers, reflecting US (SAE) and EU (ISO) specifications. Many standards are technically similar, such as SAE J1979 vs. ISO 15031-5 and SAE J1962 vs. ISO 15031-3. Adherence to these standards is crucial for ensuring that an OBD2 diagnostic cable from one manufacturer can reliably connect to and communicate with an OBD2 port on a vehicle from a different manufacturer.
Understanding the OSI model helps clarify how OBD2 and CAN bus interact and how the OBD2 diagnostic cable fits into the communication architecture.
The OBD2 connector pinout is standardized, ensuring compatibility with OBD2 diagnostic cables and tools.
The OBD2 Connector: The Interface for Your Diagnostic Cable [SAE J1962]
The 16-pin OBD2 connector is the physical interface that allows you to access your car’s data. Standardized under SAE J1962 / ISO 15031-3, this connector is designed for easy access using an OBD2 diagnostic cable. The illustration shows a typical Type A OBD2 pin connector, also known as the Data Link Connector (DLC).
Key points about the OBD2 connector:
- It’s usually located near the steering wheel, though sometimes it may be hidden behind a panel.
- Pin 16 provides battery power, often even when the ignition is off, which is important for some diagnostic functions.
- The OBD2 pinout configuration depends on the communication protocol used by the vehicle.
- CAN bus is the most prevalent lower-layer protocol, meaning pins 6 (CAN-H) and 14 (CAN-L) are commonly used for data communication when using an OBD2 diagnostic cable in modern vehicles.
OBD2 Connector Types: A vs. B and Cable Compatibility
In practice, you might encounter Type A and Type B OBD2 connectors. Type A is standard in cars, while Type B is more common in medium and heavy-duty vehicles. When choosing an OBD2 diagnostic cable, you need to be aware of these differences.
Both connector types share similar pinouts but differ in power supply outputs: Type A typically provides 12V, while Type B provides 24V. Baud rates can also vary, with cars often using 500K and heavy-duty vehicles frequently using 250K (though 500K support is increasing).
Visually, Type B connectors have an interrupted groove in the middle, distinguishing them from Type A. A Type B OBD2 adapter cable is generally compatible with both Type A and Type B sockets, while a Type A cable will only fit into a Type A socket. This is a crucial consideration when selecting the right OBD2 diagnostic cable for your needs.
Understanding the difference between OBD2 connector types A and B is essential for selecting a compatible OBD2 diagnostic cable.
The relationship between OBD2 and CAN bus highlights the communication protocols supported by the OBD2 diagnostic cable.
OBD2, CAN Bus, and Your Diagnostic Cable [ISO 15765-4]
Since 2008, CAN bus has been the mandatory lower-layer protocol for OBD2 in US vehicles, as per ISO 15765. This means that your OBD2 diagnostic cable often needs to be CAN bus compatible to effectively communicate with modern cars.
ISO 15765-4 (Diagnostics over CAN or DoCAN) defines specific restrictions for using CAN with OBD2 (ISO 11898). It standardizes the CAN interface for diagnostic equipment, focusing on the physical, data link, and network layers. These standards ensure that an OBD2 diagnostic cable designed for CAN bus communication will function correctly with compliant vehicles.
Key ISO 15765-4 specifications include:
- CAN bus bit-rate: Must be 250K or 500K.
- CAN IDs: Can be 11-bit or 29-bit.
- Specific CAN IDs are designated for OBD requests and responses.
- Diagnostic CAN frame data length: Must be 8 bytes.
- OBD2 adapter cable maximum length: 5 meters (to ensure signal integrity).
OBD2 CAN Identifiers and Diagnostic Cable Communication (11-bit, 29-bit)
OBD2 communication relies on request/response message exchanges facilitated by the OBD2 diagnostic cable.
Most cars utilize 11-bit CAN IDs for OBD2 communication. The ‘Functional Addressing’ ID, 0x7DF, is used to query all OBD2-compatible ECUs for data on a requested parameter (ISO 15765-4). ‘Physical Addressing’ requests, using CAN IDs 0x7E0-0x7E7 to target specific ECUs, are less common. The OBD2 diagnostic cable needs to be capable of transmitting and receiving data on these CAN IDs.
ECUs respond with 11-bit IDs in the range of 0x7E8-0x7EF. The most frequent response ID is 0x7E8 (ECM, Engine Control Module), followed by 0x7E9 (TCM, Transmission Control Module). A quality OBD2 diagnostic cable ensures reliable data transfer for these critical responses.
In some vehicles, especially vans and medium/heavy-duty vehicles, OBD2 communication might use extended 29-bit CAN identifiers instead of 11-bit IDs. The ‘Functional Addressing’ CAN ID in this case is 0x18DB33F1. Responses will use CAN IDs ranging from 0x18DAF100 to 0x18DAF1FF (typically 18DAF110 and 18DAF11E). These response IDs are sometimes represented in the J1939 PGN format, specifically PGN 0xDA00 (55808), which is reserved for ISO 15765-2 in the J1939-71 standard. For vehicles using 29-bit CAN IDs, the OBD2 diagnostic cable and connected tools must support this extended addressing scheme.
The request-response framework of OBD2, transmitted through the OBD2 diagnostic cable, is fundamental to vehicle diagnostics.
The distinction between OBD2 and proprietary CAN protocols highlights the standardized data accessible via the OBD2 diagnostic cable versus manufacturer-specific data.
OBD2 vs. Proprietary CAN Protocols and Cable Access
It’s important to remember that your car’s Electronic Control Units (ECUs) operate primarily on OEM-specific proprietary CAN protocols, not OBD2. OBD2 is an additional protocol layered on top for diagnostic purposes. These OEM-specific protocols are often unique to the vehicle brand, model, and year. Unless you are the OEM or have reverse-engineered these protocols, this data is generally inaccessible. A standard OBD2 diagnostic cable typically won’t provide access to this proprietary data unless specifically designed or adapted for that purpose.
When you connect a CAN bus data logger or scanner via an OBD2 diagnostic cable to your car’s OBD2 connector, you might see the OEM-specific CAN data, often broadcast at high rates (1000-2000 frames/second). However, many newer vehicles have a ‘gateway’ that blocks access to this proprietary CAN data through the OBD2 port, only allowing OBD2 communication. In these cases, the OBD2 diagnostic cable will only facilitate OBD2 data access, not direct access to the deeper OEM-specific network.
Think of OBD2 as a parallel, standardized higher-layer protocol running alongside the OEM’s proprietary communication network. The OBD2 diagnostic cable is designed to tap into this standardized diagnostic layer.
Bit-Rate, ID Validation, and Diagnostic Cable Reliability
OBD2 over CAN can use two bit-rates (250K, 500K) and two CAN ID lengths (11-bit, 29-bit), resulting in four potential combinations. Modern cars commonly use 500K and 11-bit IDs. Diagnostic tools and OBD2 diagnostic cables should be able to handle these variations and ideally perform systematic validation to determine the correct combination for a given vehicle.
ISO 15765-4 provides guidelines for initialization sequences to determine the correct bit-rate and ID combination. This process relies on the fact that OBD2-compliant vehicles must respond to a mandatory OBD2 request (PID 0x00 in mode 0x01). Using an incorrect bit-rate will result in CAN error frames. A reliable OBD2 diagnostic cable is crucial for accurate bit-rate detection and stable communication during this validation process.
Newer versions of ISO 15765-4 also consider OBD communication via OBDonUDS (OBD on Unified Diagnostic Service) in addition to OBDonEDS (OBD on Emission Diagnostic Service). While OBDonEDS (or OBD2, SAE OBD, EOBD, ISO OBD) is prevalent in most non-EV cars today, WWH-OBD/OBDonUDS is primarily used in EU trucks and buses. Advanced diagnostic tools and potentially specialized OBD2 diagnostic cables might be needed to fully support these evolving protocols.
To differentiate between OBDonEDS and OBDonUDS, diagnostic tools can send UDS requests with specific service and data identifier (DID) combinations. Vehicles supporting OBDonUDS should respond to these requests. The OBD2 diagnostic cable needs to be capable of transmitting these varied request types.
The bit-rate and CAN ID validation process ensures correct communication settings when using an OBD2 diagnostic cable.
Beyond CAN bus, OBD2 has historically utilized other lower-layer protocols, although CAN is now dominant. OBD2 diagnostic cables may need to support these legacy protocols for older vehicles.
Five Lower-Layer OBD2 Protocols and Cable Compatibility
While CAN (ISO 15765) is dominant today, older vehicles (pre-2008) may use one of four other lower-layer protocols for OBD2. Understanding these protocols and their corresponding OBD2 connector pinouts can be helpful when working with older cars and selecting the appropriate OBD2 diagnostic cable or adapter.
The five lower-layer OBD2 protocols include:
- ISO 15765 (CAN bus): Mandatory in US cars since 2008 and most common today. Modern OBD2 diagnostic cables are primarily designed for CAN.
- ISO14230-4 (KWP2000): Keyword Protocol 2000, common in 2003+ cars, particularly in Asia. Some OBD2 diagnostic cables might still support KWP2000.
- ISO 9141-2: Used in EU, Chrysler, and Asian cars in 2000-2004. Legacy OBD2 diagnostic cables might support ISO 9141-2.
- SAE J1850 (VPW): Variable Pulse Width modulation, mainly used in older GM vehicles. Specialized OBD2 diagnostic cables may be needed for J1850 VPW.
- SAE J1850 (PWM): Pulse Width Modulation, mainly used in older Ford vehicles. Specific OBD2 diagnostic cables might be required for J1850 PWM.
Transporting OBD2 Messages via ISO-TP and Your Diagnostic Cable [ISO 15765-2]
All OBD2 data communication over CAN bus utilizes the ISO-TP (ISO 15765-2) transport protocol. This protocol is essential because it allows for transmitting data payloads larger than the 8-byte limit of a single CAN frame. ISO-TP enables segmentation, flow control, and reassembly of messages, which is necessary for OBD2 functions like retrieving the Vehicle Identification Number (VIN) or Diagnostic Trouble Codes (DTCs). Your OBD2 diagnostic cable needs to facilitate this ISO-TP communication seamlessly.
However, many OBD2 data requests and responses fit within a single CAN frame. In these cases, ISO 15765-2 specifies the use of ‘Single Frame’ (SF) messages. The first data byte (PCI field) indicates the payload length, leaving 7 bytes for OBD2-related communication. Even for single-frame messages, a compliant OBD2 diagnostic cable and diagnostic tool are necessary for proper data interpretation.
Understanding ISO-TP frame types is important for interpreting OBD2 data transmitted via the OBD2 diagnostic cable, especially for multi-frame messages.
The OBD2 Diagnostic Message Structure and Your Cable’s Role [SAE J1979, ISO 15031-5]
To understand OBD2 communication using CAN bus, let’s examine the structure of a raw ‘Single Frame’ OBD2 CAN message. In simplified terms, an OBD2 message consists of a CAN identifier, a data length indicator (PCI field), and the data payload. The data payload is further divided into Mode, Parameter ID (PID), and data bytes. The OBD2 diagnostic cable is the conduit through which these messages are transmitted and received.
The OBD2 message structure, carried over the OBD2 diagnostic cable, defines how diagnostic information is organized and transmitted.
Example: OBD2 Request/Response and Cable Data Flow
Consider a practical example: requesting ‘Vehicle Speed’. A diagnostic tool, connected via an OBD2 diagnostic cable, sends a request message with CAN ID 0x7DF and a 2-byte payload: Mode 0x01 and PID 0x0D. The vehicle responds with a message via CAN ID 0x7E8 and a 3-byte payload, including the vehicle speed value in the 4th byte (0x32, which is 50 in decimal). The OBD2 diagnostic cable facilitates this two-way communication, enabling real-time data retrieval.
By referring to OBD2 PID decoding rules, we can determine that 0x32 corresponds to a vehicle speed of 50 km/h. This illustrates how the OBD2 diagnostic cable enables the extraction of meaningful vehicle parameters.
This request-response example demonstrates the data exchange facilitated by the OBD2 diagnostic cable for retrieving specific vehicle parameters.
PID 0x0D for Vehicle Speed is a common example of OBD2 data accessible through the OBD2 diagnostic cable.
OBD2 services (modes) define different diagnostic functionalities, all accessed via the OBD2 diagnostic cable.
The 10 OBD2 Services (Modes) and Cable Functionality
OBD2 defines 10 diagnostic services, also known as modes. Mode 0x01 provides current real-time data, while others are used to access and manage Diagnostic Trouble Codes (DTCs) or retrieve freeze frame data. These services are all accessed through communication via the OBD2 diagnostic cable.
Vehicles are not required to support all 10 OBD2 modes, and manufacturers may implement additional OEM-specific modes beyond the standard set. The OBD2 diagnostic cable is designed to handle the standard modes, and advanced diagnostic tools may offer support for OEM-specific modes.
In OBD2 messages, the mode is typically the second byte. In a request, the mode is included directly (e.g., 0x01). In a response, 0x40 is added to the requested mode (e.g., resulting in 0x41 for a response to mode 0x01). This mode information is part of the data transmitted through the OBD2 diagnostic cable.
OBD2 Parameter IDs (PIDs) and Diagnostic Cable Data Access
Within each OBD2 mode, Parameter IDs (PIDs) specify the particular data being requested or reported. Mode 0x01, for instance, includes approximately 200 standardized PIDs providing real-time data on parameters like speed, RPM, and fuel level. However, vehicles don’t necessarily support all PIDs within a mode. In practice, most vehicles only support a subset of the standardized PIDs. The OBD2 diagnostic cable provides the pathway to request and receive data for these supported PIDs.
One PID stands out: PID 0x00 in mode 0x01. If an emissions-related ECU supports any OBD2 services, it must support mode 0x01 PID 0x00. Responding to this PID, the ECU indicates its support for PIDs 0x01-0x20. PID 0x00 is therefore a fundamental “OBD2 compatibility test.” Similarly, PIDs 0x20, 0x40, and so on, up to 0xC0, can be used to determine support for the remaining mode 0x01 PIDs. Testing PID 0x00 is often the first step when using an OBD2 diagnostic cable to establish communication with a vehicle.
PIDs within OBD2 messages, transmitted via the OBD2 diagnostic cable, specify the exact data parameters being requested or provided.
Tools and resources are available to help understand and utilize OBD2 PIDs when working with an OBD2 diagnostic cable.
Tip: OBD2 PID Overview Tool and Cable-Based Diagnostics
SAE J1979 and ISO 15031-5 appendices provide scaling information for standard OBD2 PIDs, enabling you to convert raw data into physical values. This decoding process is essential for making sense of the data obtained through your OBD2 diagnostic cable.
For quick lookup of mode 0x01 PIDs, online OBD2 PID overview tools are available. These tools can help you construct OBD2 request frames and dynamically decode OBD2 responses, streamlining the diagnostic process when using an OBD2 diagnostic cable.
OBD2 PID overview tool
Utilize OBD2 PID overview tools to efficiently decode data retrieved through your OBD2 diagnostic cable.
How to Log and Decode OBD2 Data Using Your Diagnostic Cable
Let’s look at a practical example of logging OBD2 data using a CAN bus data logger like the CANedge, connected to your vehicle via an OBD2 diagnostic cable.
The CANedge allows you to configure custom CAN frames for transmission, making it suitable for OBD2 logging. Coupled with an OBD2-DB9 adapter cable, it easily connects to your vehicle’s OBD2 port.
An OBD2 data logger, connected via an OBD2 diagnostic cable, allows for capturing and analyzing vehicle data.
Software tools like asammdf help analyze responses and validate supported PIDs when using an OBD2 diagnostic cable.
#1: Test Bit-Rate, IDs & Supported PIDs via Diagnostic Cable Connection
As discussed, ISO 15765-4 outlines how to determine the correct bit-rate and IDs for a specific vehicle. You can perform these tests using a CANedge and an OBD2 diagnostic cable as follows:
- Transmit a CAN frame at 500K bit-rate and check for successful transmission. If unsuccessful, try 250K. The OBD2 diagnostic cable must reliably transmit these test frames.
- Use the identified bit-rate for subsequent communication via the OBD2 diagnostic cable.
- Send multiple ‘Supported PIDs’ requests through the OBD2 diagnostic cable and review the responses.
- Based on response IDs, determine whether the vehicle uses 11-bit or 29-bit CAN IDs. The OBD2 diagnostic cable must support both ID types.
- Analyze response data to identify supported PIDs.
Pre-configured settings are often available to simplify these tests. Most 2008+ non-EV cars support 40-80 PIDs using a 500K bit-rate, 11-bit CAN IDs, and the OBD2/OBDonEDS protocol. The asammdf GUI screenshot illustrates common responses to ‘Supported PIDs’ requests. Multiple responses to a single request (using ID 0x7DF) are common because it polls all ECUs. Since all OBD2/OBDonEDS-compliant ECUs must support service 0x01 PID 0x00, many responses are often seen for this PID. Subsequent ‘Supported PIDs’ requests typically receive fewer responses as fewer ECUs support those PIDs. Note that the ECM ECU (0x7E8) often supports all PIDs supported by other ECUs in the example, suggesting that bus load can be reduced by specifically targeting the ECM for subsequent requests using ‘Physical Addressing’ CAN ID 0x7E0. This optimization is relevant for efficient data logging through the OBD2 diagnostic cable.
#2: Configure OBD2 PID Requests for Logging via Diagnostic Cable
Once you know the supported PIDs, bit-rate, and CAN IDs for your vehicle, you can configure your data logger to request specific PIDs of interest via the OBD2 diagnostic cable.
Consider these factors when configuring PID requests:
- CAN IDs: Switch to ‘Physical Addressing’ request IDs (e.g., 0x7E0) to avoid multiple responses per request, optimizing data logging efficiency through the OBD2 diagnostic cable.
- Spacing: Introduce a delay of 300-500 ms between OBD2 requests. Overly frequent requests can overwhelm ECUs and lead to non-responses. Proper request spacing ensures reliable communication via the OBD2 diagnostic cable.
- Battery drain: Implement triggers to stop transmitting requests when the vehicle is inactive to prevent battery drain. This is particularly important for long-term data logging using an OBD2 diagnostic cable.
- Filters: Apply filters to record only OBD2 responses, especially if your vehicle also outputs OEM-specific CAN data. Filtering helps focus data logging on relevant OBD2 information transmitted through the OBD2 diagnostic cable.
With these configurations in place, your data logger is ready to record raw OBD2 data transmitted through the OBD2 diagnostic cable!
An example list of CANedge OBD2 PID requests for data logging via an OBD2 diagnostic cable.
asammdf allows DBC decoding and visualization of OBD2 data logged via an OBD2 diagnostic cable.
#3: DBC Decode Raw OBD2 Data from Your Diagnostic Cable Logs
To analyze and visualize logged OBD2 data, you need to decode the raw data into physical values (e.g., km/h, °C). This decoding process is applied to data captured via the OBD2 diagnostic cable.
Decoding information is found in ISO 15031-5/SAE J1979 and online resources like Wikipedia. A free OBD2 DBC file is available to simplify DBC decoding of raw OBD2 data in most CAN bus software tools. This DBC file aids in interpreting data collected through your OBD2 diagnostic cable.
Decoding OBD2 data is more complex than decoding regular CAN signals. Different OBD2 PIDs are transmitted using the same CAN ID (e.g., 0x7E8). Therefore, the CAN ID alone isn’t sufficient to identify the signals in the payload. Both the CAN ID, OBD2 mode, and OBD2 PID are needed for unique signal identification. This multiplexing method, termed ‘extended multiplexing’, can be implemented in DBC files. Using a DBC file tailored for OBD2 data significantly simplifies the process of interpreting logs obtained through your OBD2 diagnostic cable.
CANedge: OBD2 Data Logger and Diagnostic Cable Solution
The CANedge, when used with an OBD2 diagnostic cable, provides an easy way to record OBD2 data to an SD card (8-32 GB). Simply connect it to a car or truck using the OBD2 diagnostic cable to start logging. Free software and APIs, along with an OBD2 DBC file, are available for data decoding. The combination of CANedge and an OBD2 diagnostic cable offers a complete solution for OBD2 data logging and analysis.
OBD2 logger intro CANedge
The CANedge OBD2 data logger, used with an OBD2 diagnostic cable, provides a comprehensive solution for vehicle data acquisition.
OBD2 Multi-Frame Examples and Diagnostic Cable Data Transfer [ISO-TP]
All OBD2 data, including multi-frame messages, is communicated using ISO-TP (ISO 15765-2) and transmitted through the OBD2 diagnostic cable. While previous examples focused on single-frame communication, let’s examine multi-frame scenarios.
Multi-frame OBD2 communication requires flow control frames. A common approach is to transmit a static flow control frame approximately 50 ms after the initial request frame. This configuration is often used with tools like CANedge. The OBD2 diagnostic cable must reliably handle these multi-frame exchanges.
Analyzing multi-frame OBD2 responses requires CAN software and API tools that support ISO-TP, such as CANedge MF4 decoders. These tools are designed to interpret the segmented data transmitted via the OBD2 diagnostic cable in multi-frame messages.
Multi-frame requests, transmitted via the OBD2 diagnostic cable, are needed for retrieving larger datasets like the VIN.
Example 1: OBD2 Vehicle Identification Number (VIN) and Diagnostic Cable Data
Retrieving the Vehicle Identification Number (VIN) via OBD2 requests (mode 0x09, PID 0x02) often involves multi-frame communication. The OBD2 diagnostic cable is used to initiate this request and receive the multi-frame response.
The diagnostic tool sends a Single Frame request. The vehicle responds with a First Frame containing the total data length (20 bytes in this example), mode (0x49), and PID (0x02). Following the PID is the Number Of Data Items (NODI) and then the 17-byte VIN. The OBD2 diagnostic cable facilitates the transfer of this segmented VIN data. The VIN, in HEX format, can then be converted to ASCII characters.
Example 2: OBD2 Multi-PID Request and Diagnostic Cable Limitations
OBD2 allows requesting up to 6 mode 0x01 PIDs in a single request frame. The ECU responds with data for supported PIDs, potentially using multi-frame responses as per ISO-TP. While efficient, this approach complicates data decoding and may limit the usability of generic OBD2 DBC files. The OBD2 diagnostic cable is capable of handling these complex requests, but data interpretation becomes more challenging.
The multi-frame response is similar to the VIN example but includes requested PIDs and their corresponding data. The PIDs are often ordered as requested, but this is not strictly mandated by the ISO 15031-5 standard. Decoding such responses using generic DBC files is difficult due to the complex multiplexing and variable payload structure. While technically feasible via the OBD2 diagnostic cable, multi-PID requests are generally not recommended for practical data logging unless specialized tools and custom DBCs are used.
Example 3: OBD2 Diagnostic Trouble Codes (DTCs) and Your Diagnostic Cable
Requesting emissions-related Diagnostic Trouble Codes (DTCs) using mode 0x03 also utilizes multi-frame communication when more than a few DTCs are stored. The OBD2 diagnostic cable is used to send the DTC request and receive the potentially multi-frame response containing the DTC information.
DTC decoding involves understanding the structure of the 2-byte DTC values transmitted via the OBD2 diagnostic cable.
The 2-byte DTC value is categorized and contains a 4-digit hexadecimal code. Decoded DTC values can be looked up using OBD2 DTC lookup tools. The example shows a request to an ECU with 6 stored DTCs, requiring a multi-frame response transmitted via the OBD2 diagnostic cable.
OBD2 Data Logging Use Cases and Your Diagnostic Cable Applications
OBD2 data logging, enabled by the OBD2 diagnostic cable and logging tools, has numerous applications for cars and light trucks:
Logging data from cars and light trucks
OBD2 data logs, captured via an OBD2 diagnostic cable, can be used for fuel efficiency analysis, driving behavior improvement, prototype testing, and insurance telematics.
obd2 logger
OBD2 data logging via a diagnostic cable enables various applications, from fuel efficiency to driver behavior analysis.
Real-time car diagnostics
OBD2 interfaces, connected via an OBD2 diagnostic cable, enable real-time streaming of human-readable OBD2 data for immediate vehicle issue diagnosis.
obd2 streaming
Real-time OBD2 data streaming, facilitated by an OBD2 diagnostic cable, is crucial for efficient vehicle diagnostics.
Predictive maintenance
IoT-enabled OBD2 loggers, connected via an OBD2 diagnostic cable, allow for remote vehicle monitoring to predict and prevent breakdowns.
predictive maintenance
Predictive maintenance leverages OBD2 data, accessed via a diagnostic cable and IoT connectivity, to anticipate vehicle issues.
Vehicle black box logger
An OBD2 logger, connected via an OBD2 diagnostic cable, can serve as a ‘black box’ for vehicles or equipment, providing data for accident analysis, disputes, or diagnostics.
can bus blackbox
As a vehicle black box, an OBD2 logger and diagnostic cable can record crucial data for various purposes, including insurance and diagnostics.
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