Free OBD2 Connector Explained: Your Guide to On-Board Diagnostics

Want to understand your car’s health without breaking the bank?

This guide provides a practical introduction to the On-Board Diagnostic (OBD2) system, focusing on the accessible and standardized OBD2 connector. We’ll demystify the OBD2 protocol, including the connector itself, OBD2 Parameter IDs (PIDs), and its connection to the CAN bus network in your vehicle.

This is more than just an introduction; it’s a hands-on guide to understanding and utilizing OBD2 data. You’ll learn how to request and interpret OBD2 information, explore key applications for data logging, and gain practical tips to get started – all while understanding the concept of a “Free Obd2 Connector” in terms of accessibility and readily available information.

Discover why this is becoming a go-to resource for anyone looking to dive into the world of OBD2 diagnostics.

You can also watch our OBD2 intro video above – or get the PDF guide

Understanding the OBD2 System and Your Free OBD2 Connector Access Point

OBD2 is essentially your car’s built-in health monitor. It’s a standardized system designed to provide access to diagnostic trouble codes (DTCs) and real-time vehicle data through what we can consider a “free OBD2 connector” – free in the sense that it’s a standard, openly specified port readily available in almost all modern vehicles for diagnostic purposes.

You’re likely already familiar with OBD2 without realizing it:

Ever seen the check engine light, officially known as the malfunction indicator light, illuminate on your dashboard?

That’s your car signaling a potential issue. When you take your vehicle to a mechanic, they use an OBD2 scanner to pinpoint the problem. This process begins with connecting the OBD2 reader to the OBD2 16 pin connector, typically located within easy reach near the steering wheel. This “free OBD2 connector” acts as the gateway, allowing diagnostic tools to send ‘OBD2 requests’ to the car’s computer. The car then responds with ‘OBD2 responses’, which can include a wealth of information like speed, fuel level, and those crucial Diagnostic Trouble Codes (DTCs). This streamlined communication drastically speeds up troubleshooting and repair processes.

Understanding OBD2: The malfunction indicator light (MIL) on your dashboard signals issues, diagnosed via the OBD2 port.

Is There a Free OBD2 Connector in My Car? Vehicle Compatibility Explained

The short answer is: Almost certainly, yes!

The beauty of OBD2 is its widespread adoption. Nearly all modern gasoline and diesel cars (non-electric) are equipped with OBD2 support, and most of these systems operate on the CAN bus communication protocol. While older vehicles might feature a 16-pin connector resembling an OBD2 port, it’s important to note that the presence of a 16-pin “look-alike” doesn’t guarantee true OBD2 compliance. To confirm if your vehicle truly supports OBD2, consider its origin and year of purchase:

OBD2 Compatibility Guide: Check your vehicle’s origin and purchase year to determine OBD2 compliance.

The History of OBD2: From Emission Control to Free Access to Vehicle Data

The OBD2 story begins in California, driven by the California Air Resources Board (CARB). Starting in 1991, CARB mandated OBD systems in all new vehicles sold in California for the purpose of rigorous emission control.

The Society of Automotive Engineers (SAE) played a crucial role by recommending the OBD2 standard, which standardized both DTCs and, importantly, the OBD connector itself across all vehicle manufacturers (SAE J1962). This standardization is key to the idea of a “free OBD2 connector” – it’s a universally accessible point, not locked behind proprietary systems.

The OBD2 standard was implemented globally in stages:

1996: OBD2 became mandatory in the USA for all cars and light trucks.
2001: The European Union mandated OBD2 for gasoline cars.
2003: The EU extended the mandate to diesel cars as well (known as EOBD in Europe).
2005: OBD2 was required 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 mandatory for heavy-duty vehicles in the US.

OBD2 Historical Timeline: From emission control origins to global standardization for vehicle diagnostics.

OBD2 Evolution: A visual timeline of the on-board diagnostics history and standardization milestones.

The Future of OBD: Exploring OBD3 trends, remote diagnostics, and integration with cloud and IoT technologies.

The Future of OBD2: Trends and the Evolving Role of the Free OBD2 Connector

OBD2 is firmly established, but its future form is subject to change. Let’s explore some key trends:

Originally, legislated OBD2 was primarily for emissions control and testing. Interestingly, this means electric vehicles (EVs) are not obligated to support OBD2 in any form. In fact, most modern EVs deviate from standard OBD2 requests, opting for OEM-specific UDS communication protocols instead. This shift often makes it challenging to access data from EVs unless decoding methods are reverse-engineered. However, there are successful cases of reverse engineering, as demonstrated in studies for electric cars like Tesla, Hyundai/Kia, Nissan, and VW/Skoda EVs.

OBD2 implementations today are diverse and face limitations in data richness and lower-layer protocols. To address these, modern alternatives like WWH-OBD (World Wide Harmonized OBD) and OBDonUDS (OBD on UDS) have emerged. Both aim to improve OBD communication by using the UDS protocol as a foundation. Learn more about these protocols in our introduction to UDS.

In our increasingly connected world, traditional OBD2 emission tests can feel outdated. Manual checks are time-consuming and costly. The proposed solution? OBD3 – integrating telematics into all vehicles.

OBD3 envisions adding a small radio transponder (similar to those used for bridge tolls) to every car. This would enable the car’s vehicle identification number (VIN) and DTCs to be transmitted wirelessly via WiFi to a central server for automated checks.

Many existing devices already facilitate CAN or OBD2 data transfer via WiFi/cellular, such as the CANedge2 WiFi CAN logger and the CANedge3 3G/4G CAN logger. While this offers cost savings and convenience, it also raises political and privacy concerns related to increased surveillance.

The original purpose of the OBD2 protocol was for stationary emission controls. However, third-party use of OBD2 for real-time data generation has become widespread, utilizing OBD2 dongles, CAN loggers and similar tools. This growing third-party access has sparked debate, particularly within the German car industry, which seeks to regain control over vehicle data access:

OBD was intended for car servicing in repair shops, not for third parties to build a data-driven economy based on this interface.

– Christoph Grote, SVP Electronics, BMW (2017)

The proposal is to potentially disable OBD2 functionality during driving and instead centralize data collection within manufacturer servers. This would place car manufacturers in control of the burgeoning ‘automotive big data’.

Arguments for this shift often cite security concerns, such as mitigating the risk of car hacking. However, critics view this as a commercially motivated move to control valuable data, potentially disrupting the market for third-party OBD2 services. Whether this trend gains traction remains to be seen, but it could significantly reshape the landscape of OBD2 and the concept of a “free OBD2 connector” as an open access point.

OBD2 Access Restrictions: The trend of electric vehicles limiting data access via the OBD2 connector.

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OBD2 Standards: Defining the “Free OBD2 Connector” and Communication Protocols

On-board diagnostics, or OBD2, operates as a higher layer protocol – think of it as a language spoken by your car’s computers. CAN (Controller Area Network) bus, on the other hand, is the communication method, like a telephone line. This places OBD2 in the same category as other CAN-based higher-layer protocols such as J1939, CANopen, and NMEA 2000.

OBD2 standards rigorously define the “free OBD2 connector” specifications, lower-layer communication protocols, OBD2 Parameter IDs (PIDs), and much more. These standards ensure interoperability and the ability to freely access diagnostic information using standardized tools.

These standards can be visualized using the 7-layer OSI model. Notably, both SAE (primarily US standards) and ISO (international standards, often adopted in the EU) cover various layers. Many standards are technically very similar, for example, SAE J1979 is closely related to ISO 15031-5, and SAE J1962 mirrors ISO 15031-3.

OBD2 and CAN Bus in the OSI Model: Illustrating the layers defined by ISO and SAE standards for vehicle communication.

OBD2 Connector Pinout: Diagram of a Type A OBD2 connector (Data Link Connector – DLC) socket and pin assignments.

The OBD2 Connector [SAE J1962 / ISO 15031-3]: Your Free Access Point

The standardized 16-pin OBD2 connector, detailed in SAE J1962 and ISO 15031-3, provides straightforward access to your vehicle’s data. This “free OBD2 connector” in terms of open specification, is designed for easy access and diagnostic tool connection.

The illustration above shows a typical Type A OBD2 pin connector (sometimes called the Data Link Connector, or DLC).

Key features of the OBD2 connector to note:

It’s usually located near the steering wheel, although it may be somewhat hidden behind a panel.
Pin 16 provides battery power, often even when the ignition is off, allowing diagnostic tools to function.
The specific 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 connected for data communication.

OBD2 Connector Types: A vs. B

In practical applications, you might encounter both Type A and Type B OBD2 connectors. Type A is the standard in most passenger cars and light vehicles, while Type B is more common in medium and heavy-duty vehicles.

As the illustration shows, both types share a similar OBD2 pinout structure, but they differ in power supply output: Type A typically provides 12V, while Type B provides 24V. Baud rates can also vary, with cars usually using 500K and heavy-duty vehicles often using 250K (though 500K support is increasing).

A distinguishing physical feature is that the Type B OBD2 connector has an interrupted groove in the center. This means a Type B OBD2 adapter cable will be compatible with both Type A and Type B sockets, whereas a Type A adapter will only fit into a Type A socket.

OBD2 Connector Types A and B: Illustrating the differences in pin configuration, voltage, and application.

OBD2 and CAN Bus Interrelation: Depicting the relationship between OBD2 protocol and the underlying CAN bus communication.

OBD2 and CAN Bus [ISO 15765-4]: Communication Standards for Your Free OBD2 Connector

Since 2008, CAN bus has been the mandated lower-layer protocol for OBD2 in all vehicles sold in the US, as per ISO 15765. This standard ensures consistent communication through the “free OBD2 connector”.

ISO 15765-4 (also known as Diagnostics over CAN, or DoCAN) specifies a set of constraints applied to the CAN standard (ISO 11898) for diagnostic purposes.

Specifically, it standardizes the CAN interface for diagnostic equipment, focusing on the physical, data link, and network layers:

CAN bus bit-rate must be either 250K or 500K.
CAN IDs can be 11-bit or 29-bit.
Specific CAN IDs are designated for OBD requests and responses.
The diagnostic CAN frame data length is fixed at 8 bytes.
The OBD2 adapter cable must be a maximum of 5 meters in length.

OBD2 CAN Identifiers (11-bit, 29-bit)

All OBD2 communication involves a request-response message exchange.

In most passenger vehicles, 11-bit CAN IDs are used for OBD2 communication. The ‘Functional Addressing’ ID is 0x7DF, which is used to query all OBD2-compatible ECUs (Electronic Control Units) to see if they have data relevant to the requested parameter (as defined in ISO 15765-4). In contrast, CAN IDs in the range 0x7E0-0x7E7 can be used for ‘Physical Addressing’ requests, targeting specific ECUs (though this is less common).

ECUs respond using 11-bit IDs in the range 0x7E8-0x7EF. The most common response ID is 0x7E8 (from the ECM, Engine Control Module), followed by 0x7E9 (from the TCM, Transmission Control Module).

In some vehicle types, especially vans and medium to heavy-duty vehicles, OBD2 communication might use extended 29-bit CAN identifiers instead of the 11-bit format.

Here, the ‘Functional Addressing’ CAN ID is 0x18DB33F1.

Responses in 29-bit CAN ID systems are typically found in the range 0x18DAF100 to 0x18DAF1FF (common examples are 18DAF110 and 18DAF11E). This response ID is sometimes represented in the ‘J1939 PGN’ format, specifically PGN 0xDA00 (55808), which in the J1939-71 standard is marked as ‘Reserved for ISO 15765-2’.

OBD2 Request and Response Frames: Illustrating the structure of OBD2 communication frames with PID data parameters.

OBD2 vs. Proprietary CAN Bus: Contrasting standardized OBD2 data with OEM-specific CAN bus information.

OBD2 vs. Proprietary CAN Protocols: Understanding Data Access Beyond the Free OBD2 Connector

It’s crucial to understand that your car’s electronic control units (ECUs) do not rely on OBD2 for their primary functions. Instead, each Original Equipment Manufacturer (OEM) develops and implements its own proprietary CAN protocols for internal vehicle communication. These proprietary CAN protocols are often specific to the vehicle brand, model, and production year. For individuals outside the OEM, interpreting this proprietary data is typically not possible without significant effort in reverse engineering.

When you connect a CAN bus data logger to your car’s “free OBD2 connector,” you might observe OEM-specific CAN data being broadcast, often at a high rate of 1000-2000 frames per second. However, many newer vehicles incorporate a ‘gateway’ module that restricts access to this proprietary CAN data via the OBD2 port, allowing only standardized OBD2 communication.

In essence, think of OBD2 as a separate, ‘add-on’ higher-layer protocol running parallel to the OEM-specific communication network. While the physical connector may be “free” and standardized, access to the deeper, proprietary vehicle data remains controlled by the manufacturer.

Bit-rate and ID Validation for Reliable OBD2 Communication

As mentioned, OBD2 communication can operate at two different bit rates (250K, 500K) and use either 11-bit or 29-bit CAN IDs. This results in four potential combinations. In modern cars, 500K bit-rate and 11-bit IDs are the most common, but external tools should systematically verify the correct combination for reliable communication.

ISO 15765-4 provides guidelines for a systematic initialization sequence to determine the correct communication parameters. This method relies on the fact that OBD2-compliant vehicles must respond to a specific mandatory OBD2 request (see the OBD2 PID section for details) and that transmitting data at an incorrect bit-rate will generate CAN error frames.

Newer versions of ISO 15765-4 acknowledge that vehicles may support OBD communication via OBDonUDS (OBD on Unified Diagnostic Services) rather than the more traditional OBDonEDS (OBD on Emission Diagnostic Service). This article primarily focuses on OBD2/OBDonEDS (as per ISO 15031-5/SAE J1979) as opposed to WWH-OBD/OBDonUDS (as per ISO 14229, ISO 27145-3/SAE J1979-2).

To differentiate between OBDonEDS and OBDonUDS protocols, a diagnostic tool can send additional request messages, specifically UDS requests with 11-bit/29-bit functional address IDs for service 0x22 and data identifier (DID) 0xF810 (protocol identification). Vehicles supporting OBDonUDS should have ECUs that respond to this DID.

In practice, OBDonEDS (also known as OBD2, SAE OBD, EOBD, or ISO OBD) is predominantly used in non-EV cars today, while WWH-OBD is more common in EU trucks and buses.

OBD2 Bit-rate and CAN ID Validation Flowchart: Illustrating the process for automatically determining the correct communication parameters.

Five Lower-Layer OBD2 Protocols: Diagram showing the different communication protocols used in OBD2 systems.

Five Lower-Layer OBD2 Protocols: Beyond CAN Bus

While CAN bus (ISO 15765) is now the dominant lower-layer protocol for OBD2 in most vehicles, especially post-2008 models, older cars may utilize other protocols. Understanding these alternative protocols can be useful, particularly when working with older vehicles. The pinout of the “free OBD2 connector” can sometimes provide clues about the protocol in use.

Here are the five primary lower-layer protocols used for OBD2:

ISO 15765 (CAN bus): Mandatory in US vehicles since 2008 and widely used in modern vehicles.
ISO14230-4 (KWP2000): Keyword Protocol 2000, common in 2003+ vehicles, particularly in Asia.
ISO 9141-2: Used in EU, Chrysler, and Asian vehicles from approximately 2000-2004.
SAE J1850 (VPW – Variable Pulse Width Modulation): Primarily used in older General Motors (GM) vehicles.
SAE J1850 (PWM – Pulse Width Modulation): Primarily used in older Ford vehicles.

Transporting OBD2 Messages via ISO-TP [ISO 15765-2]: Handling Larger Data Payloads

All OBD2 data transmitted over CAN bus utilizes a transport protocol called ISO-TP (ISO 15765-2). This protocol is essential because it enables the communication of data payloads larger than the 8-byte limit of a standard CAN frame. This capability is necessary in OBD2 for tasks like retrieving the Vehicle Identification Number (VIN) or Diagnostic Trouble Codes (DTCs), which often require more than 8 bytes of data. ISO 15765-2 handles data segmentation, flow control, and reassembly to manage these larger messages. For a deeper dive, see our introduction to UDS.

However, much of the routine OBD2 data transmission fits within a single CAN frame. In these cases, ISO 15765-2 specifies the use of ‘Single Frame’ (SF) messages. In a Single Frame, the first data byte (known as the PCI or Protocol Control Information field) indicates the payload length (excluding any padding bytes), leaving 7 bytes available for the actual OBD2 communication data.

ISO-TP Frame Types for OBD2: Illustrating the different frame formats used in ISO 15765-2 for OBD2 communication.

The OBD2 Diagnostic Message [SAE J1979, ISO 15031-5]: Decoding the Data from Your Free OBD2 Connector

To better understand how OBD2 functions over CAN, let’s examine the structure of a raw ‘Single Frame’ OBD2 CAN message. In simple terms, an OBD2 message consists of a CAN identifier, a data length indicator (PCI field), and the data itself. The data portion is further broken down into a Mode byte, a Parameter ID (PID), and the actual data bytes.

OBD2 Message Structure: Breakdown of a raw OBD2 CAN frame, showing Mode, PID, and data byte components.

Example: OBD2 Request and Response – Getting Vehicle Speed Data

Before diving into the details of each part of an OBD2 message, let’s look at a practical example: requesting and receiving vehicle speed data.

In this scenario, an external diagnostic tool sends a request message to the vehicle with CAN ID 0x7DF and a 2-byte payload: Mode 0x01 and PID 0x0D. The vehicle responds with a message using CAN ID 0x7E8 and a 3-byte payload. This payload includes the vehicle speed value in the 4th byte of the CAN data frame, represented as 0x32 (which is 50 in decimal).

By consulting the OBD2 PID specifications for PID 0x0D, we can determine that this value represents vehicle speed in km/h. Thus, 0x32 corresponds to a speed of 50 km/h. This demonstrates how data accessed through the “free OBD2 connector” is structured and interpreted.

OBD2 Request/Response Example: Requesting vehicle speed (PID 0x0D) and the corresponding response.

OBD2 PID 0D – Vehicle Speed: Detailed explanation of PID 0x0D and its data interpretation for vehicle speed.

OBD2 Services (Modes): Overview of the 10 standardized OBD2 service modes and their diagnostic functions.

The 10 OBD2 Services (Modes): Accessing Different Types of Diagnostic Information

The OBD2 standard defines 10 diagnostic services, often referred to as modes. Each mode provides access to different categories of diagnostic information. Mode 0x01, for example, is used to retrieve current real-time data parameters, while other modes are used to access and clear diagnostic trouble codes (DTCs), or to retrieve freeze frame data (snapshots of data taken when a DTC was set).

It’s important to note that vehicles are not required to support all 10 OBD2 modes. Manufacturers can also implement modes beyond these 10 standardized ones, known as OEM-specific OBD2 modes, for accessing more specialized diagnostic information.

In OBD2 messages, the mode is indicated in the second byte of the data payload. In a request message, the mode is included directly (e.g., 0x01 for Mode 1). In a response message, 0x40 is added to the requested mode (e.g., a response to Mode 0x01 will have a mode byte of 0x41).

OBD2 Parameter IDs (PIDs): Specifying the Data You Need

Within each OBD2 mode, Parameter IDs (PIDs) are used to specify the particular data parameter being requested or reported.

For example, Mode 0x01, which deals with real-time data, includes approximately 200 standardized PIDs. These PIDs cover a wide range of parameters, such as vehicle speed, engine RPM, and fuel level. However, a vehicle does not have to support all of these PIDs within Mode 0x01. In practice, most vehicles support only a subset of the standardized PIDs.

Among the PIDs, one stands out as particularly important: PID 0x00 in Mode 0x01. If an emissions-related ECU supports any OBD2 services, it must support Mode 0x01 PID 0x00. When queried with this PID, the vehicle’s ECU responds with a bitmask indicating which PIDs in the range 0x01-0x20 it supports. This makes PID 0x00 a fundamental tool for “OBD2 compatibility testing.” Similarly, PIDs 0x20, 0x40, 0x60, 0x80, 0xA0, and 0xC0 are used to determine support for subsequent ranges of Mode 0x01 PIDs (0x21-0x40, 0x41-0x60, and so on).

OBD2 Request and Response Frames: Reiterating the structure for PID-based data requests and responses.

OBD2 PID Overview Tool: Screenshot of a tool designed to help navigate and understand OBD2 PIDs for service 0x01.

Tip: Utilizing an OBD2 PID Overview Tool for Easy Access to Data

The appendices of SAE J1979 and ISO 15031-5 provide detailed scaling and conversion information for standard OBD2 PIDs. This information is essential for accurately decoding the raw data received from your “free OBD2 connector” into meaningful physical values (as explained in our CAN bus introduction).

If you need to quickly look up a specific Mode 0x01 PID, our OBD2 PID overview tool is a valuable resource. It simplifies the process of constructing OBD2 request frames and dynamically decoding the responses you receive from your vehicle.

OBD2 PID overview tool

How to Log and Decode OBD2 Data: Practical Steps for Using Your Free OBD2 Connector

This section provides a practical guide on logging OBD2 data using a CANedge CAN bus data logger. The CANedge is configurable to transmit custom CAN frames, making it ideal for OBD2 data logging.

Once configured, you can easily connect the CANedge to your vehicle’s “free OBD2 connector” using our OBD2-DB9 adapter cable.

OBD2 Data Logger Setup: Connecting an OBD2 data logger to request PIDs and capture vehicle data.

OBD2 Bit Rate Validation: Testing the CAN bit rate for successful communication with the vehicle’s OBD2 system.

Supported PIDs Validation: Reviewing responses in asammdf to identify supported OBD2 PIDs.

Step #1: Validate Bit-rate, CAN IDs, and Supported PIDs

As previously discussed, ISO 15765-4 outlines how to determine the correct bit-rate and CAN IDs for a specific vehicle. You can use the CANedge to perform these validation steps as follows (see the CANedge Intro for detailed instructions):

Bit-rate Test: Send a CAN frame at 500K bit-rate and check for successful transmission. If unsuccessful, try 250K bit-rate.
Bit-rate Confirmation: Use the validated bit-rate for all subsequent OBD2 communication.
Supported PIDs Discovery: Send multiple ‘Supported PIDs’ requests (Mode 0x01 PID 0x00, PID 0x20, etc.) and examine the responses.
CAN ID Type Determination: Based on the response IDs received, determine whether the vehicle uses 11-bit or 29-bit CAN IDs for OBD2.
Supported PID List: Analyze the response data to create a list of PIDs supported by your vehicle.

We provide ready-to-use configuration files for CANedge to automate these initial tests.

Most non-electric vehicles manufactured in 2008 or later typically support 40-80 PIDs, using a 500K bit-rate, 11-bit CAN IDs, and the OBD2/OBDonEDS protocol.

As shown in the asammdf GUI screenshot, it’s common to receive multiple responses to a single OBD request, especially when using the functional request ID 0x7DF, which polls all ECUs. Since all OBD2/OBDonEDS-compliant ECUs must support service 0x01 PID 0x00, many ECUs often respond to this initial request. As you proceed with requests for subsequent ‘Supported PIDs’ ranges, you’ll typically see fewer ECUs responding. Note that the ECM (0x7E8) often supports all PIDs supported by other ECUs in the vehicle. Therefore, to reduce bus load and streamline communication, you can switch to ‘Physical Addressing’ using CAN ID 0x7E0 for subsequent requests, targeting the ECM specifically.

Step #2: Configure OBD2 PID Requests for Data Logging

Once you’ve identified the supported OBD2 PIDs for your vehicle and determined the correct bit-rate and CAN IDs, you can configure your data logger to request specific PIDs of interest.

Consider these points when configuring your OBD2 PID requests:

CAN Addressing: Switch to ‘Physical Addressing’ request IDs (e.g., 0x7E0) to target specific ECUs and avoid redundant responses.
Request Spacing: Introduce a delay of 300-500 milliseconds between consecutive OBD2 requests. Overly rapid requests can overwhelm ECUs and lead to non-responses.
Power Management: Implement triggers to stop PID requests when the vehicle is inactive. This prevents unnecessary battery drain and avoids ‘waking up’ ECUs when the vehicle is off.
Data Filtering: Set up filters to record only OBD2 response messages, especially if your vehicle also broadcasts OEM-specific CAN data on the same network.

With these configurations in place, your data logger is ready to efficiently capture raw OBD2 data from your vehicle’s “free OBD2 connector.”

CANedge OBD2 Request Configuration: Example transmit list for CANedge showing configured OBD2 PID requests.

Decoded OBD2 Data Visualization: asammdf screenshot showing DBC-decoded and visualized OBD2 data.

Step #3: DBC Decode Raw OBD2 Data for Analysis

To effectively analyze and visualize the logged OBD2 data, you need to decode the raw data bytes into ‘physical values’ (e.g., kilometers per hour, degrees Celsius).

The necessary decoding information is defined in ISO 15031-5/SAE J1979 and is also available in resources like Wikipedia. For convenience, we offer a free OBD2 DBC file. This DBC file simplifies the process of DBC decoding raw OBD2 data within most CAN bus software tools.

Decoding OBD2 data is somewhat more complex than decoding standard CAN signals. This complexity arises because different OBD2 PIDs are transmitted using the same CAN ID (e.g., 0x7E8). Therefore, the CAN ID alone is not sufficient to uniquely identify the signals within the payload.

To address this, decoding must consider the CAN ID, the OBD2 mode, and the specific OBD2 PID to correctly identify each signal. This method is a form of multiplexing called ‘extended multiplexing‘, which is effectively implemented in DBC files. Our provided OBD2 DBC file is designed to handle this extended multiplexing and streamline your OBD2 data analysis.

CANedge: Your Dedicated OBD2 Data Logger

The CANedge offers a user-friendly solution for recording OBD2 data directly to a removable 8-32 GB SD card. Simply connect it to your vehicle’s “free OBD2 connector” to begin logging. Analyze and decode your data using free software and APIs in conjunction with our OBD2 DBC file.

OBD2 logger intro
CANedge Product Details

OBD2 Multi-Frame Examples [ISO-TP]: Handling Larger Diagnostic Responses

All OBD2 communication is managed using the ISO-TP (transport protocol) as per ISO 15765-2. While many examples discussed so far involve single-frame communication, this section explores examples of multi-frame communication, which is necessary for larger diagnostic responses.

Multi-frame OBD2 communication requires the use of flow control frames (see our UDS introduction for details on flow control in diagnostic protocols). In practice, a static flow control frame can be transmitted approximately 50 milliseconds after the initial request frame to manage multi-frame responses, as illustrated in the CANedge configuration example.

Analyzing multi-frame OBD2 responses requires CAN software and API tools that support ISO-TP, such as the CANedge MF4 decoders.

OBD2 Multi-Frame Request Example: Requesting Vehicle Identification Number (VIN) using a multi-frame request message.

Example 1: OBD2 Vehicle Identification Number (VIN) Retrieval

The Vehicle Identification Number (VIN) is crucial for various applications, including telematics and vehicle diagnostics (see our UDS introduction for more context). To retrieve the VIN from a vehicle using OBD2 requests, you use Mode 0x09 (Request Vehicle Information) and PID 0x02 (Request VIN):

The diagnostic tool sends a Single Frame request with the PCI field (0x02), request service identifier (0x09), and PID (0x02).

The vehicle responds with a First Frame containing the PCI, total message length (0x014 = 20 bytes), mode (0x49, which is 0x09 + 0x40), and PID (0x02). Following the PID is the byte 0x01, representing the Number Of Data Items (NODI), which is 1 in this case (refer to ISO 15031-5 / SAE J1979 for detailed specifications). The subsequent 17 bytes contain the VIN, which can be translated from hexadecimal to ASCII characters using methods discussed in our UDS introduction.

Example 2: OBD2 Multi-PID Request (Requesting Data for Up to 6 PIDs)

OBD2 allows diagnostic tools to request data for up to 6 Mode 0x01 PIDs in a single request frame. The ECU is expected to respond with data for all supported PIDs from the request (omitting data for any unsupported PIDs), potentially using multi-frame responses via ISO-TP if the data exceeds a single frame.

This multi-PID request feature can improve data collection efficiency, allowing you to gather more data at a higher frequency. However, it also introduces complexities in signal encoding, making the use of generic OBD2 DBC files more challenging for such requests. We generally do not recommend using multi-PID requests for standard data logging purposes due to these complexities. Below is an example trace of a multi-PID request:

The multi-frame response structure is similar to the VIN example, but with the added complexity that the payload includes both the requested PIDs themselves and the corresponding data for each PID. In the example, the PIDs in the response are ordered similarly to the order in which they were requested, which is common practice but not strictly mandated by the ISO 15031-5 standard.

Decoding these multi-PID responses using generic DBC files is very difficult and generally not recommended for practical data logging unless you are using a tool specifically designed to handle this type of response. You would be dealing with a complex case of extended multiplexing, where the DBC file would need to account for the specific payload position of each PID, making it challenging to create a generalized DBC file applicable across different vehicles with varying PID support. Furthermore, managing this becomes exceedingly difficult if you send multiple such multi-PID requests, as you would lack a straightforward method to differentiate between these messages based solely on CAN IDs.

Workarounds might involve custom scripting and recording both the request and response messages, allowing a script to interpret the response based on the preceding request. However, such approaches are complex to scale and manage for large-scale data analysis.

Example 3: OBD2 Diagnostic Trouble Codes (DTCs) Retrieval

You can use OBD2 to request emissions-related Diagnostic Trouble Codes (DTCs) using Mode 0x03, ‘Show stored Diagnostic Trouble Codes’. No PID is included in the request for this mode. The targeted ECU(s) will respond with the number of DTCs currently stored (which could be zero if no DTCs are active), with each DTC being represented by 2 data bytes. Multi-frame responses are necessary when more than two DTCs are stored due to the data payload size.

The 2-byte DTC value is typically structured into two parts, as defined by ISO 15031-5/ISO 15031-6. The first two bits indicate the DTC ‘category’ (e.g., Powertrain, Chassis, Body, Network), and the remaining 14 bits form a 4-digit code (displayed in hexadecimal format), as shown in the visual. Decoded DTC values can be looked up using various online OBD2 DTC lookup tools, such as repairpal.com.

The example below illustrates a request to an ECU that has 6 DTCs stored.

OBD2 DTC Decoding Example: Illustrating the structure and interpretation of Diagnostic Trouble Code data bytes.

OBD2 Data Logging – Real-World Use Case Examples

OBD2 data, easily accessible through the “free OBD2 connector” in cars and light trucks, has numerous practical applications:

Vehicle Data Logging for Cars

OBD2 data logging in passenger cars can be used to achieve various benefits, including reducing fuel consumption, improving driving habits, testing prototype components, and optimizing insurance premiums based on driving behavior.

OBD2 Logger Solutions

Real-time Vehicle Diagnostics

OBD2 interfaces facilitate real-time streaming of vehicle data in a human-readable format. This is invaluable for on-the-spot vehicle diagnostics, allowing technicians and enthusiasts to quickly identify and troubleshoot vehicle issues.

OBD2 Real-time Streaming Interfaces

Predictive Maintenance Applications

Cloud-connected IoT OBD2 loggers enable continuous monitoring of vehicle health, allowing for predictive maintenance strategies. By analyzing OBD2 data in the cloud, potential breakdowns can be predicted and proactively addressed, minimizing downtime and repair costs.

Predictive Maintenance Solutions

Vehicle Black Box Recording

An OBD2 data logger can serve as a ‘black box’ for vehicles or equipment, continuously recording critical vehicle parameters. This recorded data can be invaluable in resolving disputes, investigating accidents, or providing detailed diagnostics information for warranty claims.

CAN Bus Black Box Loggers

Do you have a specific OBD2 data logging application in mind? Contact us for a free consultation and expert advice!

For more in-depth introductions to related topics, explore our guides section or download the comprehensive ‘Ultimate Guide’ PDF.

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Recommended Resources for Further Learning

OBD2 DATA LOGGER: EASILY LOG & CONVERT OBD2 DATA

CANEDGE2 – PRO CAN IoT LOGGER

CAN BUS INTERFACE: STREAMING OBD2 DATA WITH SAVVYCAN