Understanding OBD2 Protocols: A Comprehensive Guide for Automotive Diagnostics

Need a clear and in-depth explanation of Obd2 Protocols?

This guide provides a comprehensive overview of On-Board Diagnostics 2 (OBD2) protocols, essential for anyone involved in vehicle diagnostics, repair, or data analysis. We will delve into the intricacies of OBD2 communication, covering everything from the OBD2 connector and communication standards to Parameter IDs (PIDs) and the role of protocols like CAN bus.

Whether you are a seasoned automotive technician or just beginning to explore vehicle diagnostics, this article will equip you with the knowledge to understand and utilize OBD2 protocols effectively.

You can also refer to our OBD2 introduction video or download our comprehensive PDF guide for offline access.

What are OBD2 Protocols?

OBD2 protocols are the standardized communication rules that govern how diagnostic tools interact with a vehicle’s On-Board Diagnostic system. OBD2 itself is a vehicle’s self-diagnostic and reporting capability. When you see the malfunction indicator light (MIL), often called the “check engine light,” illuminate on your dashboard, it’s a sign that the OBD2 system has detected an issue.

To diagnose these issues, mechanics and technicians use OBD2 scanners. These scanners connect to the vehicle’s 16-pin OBD2 connector, typically located under the dashboard near the steering wheel. The scanner communicates with the vehicle’s computer systems using specific OBD2 protocols. These protocols define the language and method of communication, enabling the scanner to send requests and receive responses containing valuable data such as:

Diagnostic Trouble Codes (DTCs): Codes that pinpoint specific faults within the vehicle systems.
Real-time Parameter Data: Live readings from sensors throughout the vehicle, like speed, engine RPM, coolant temperature, and fuel level.

Essentially, OBD2 protocols are the foundation for efficient and standardized vehicle diagnostics, allowing for quicker troubleshooting and repair.

OBD2 Protocol Compliance: Is Your Car Supported?

The likelihood of your car supporting OBD2 protocols is very high, especially if it’s a newer, non-electric vehicle. OBD2 has become a near-universal standard for vehicles across the globe. While most modern cars with a 16-pin connector do support OBD2, older vehicles with the same connector might not be fully compliant.

To confirm OBD2 compliance, consider the vehicle’s origin and year of purchase:

A Brief History of OBD2 Protocol Development

The story of OBD2 protocols begins in California, driven by the California Air Resources Board (CARB). In the early 1990s, CARB mandated on-board diagnostics for all new vehicles sold in California starting from 1991, primarily for emission control.

The Society of Automotive Engineers (SAE) played a crucial role in standardizing these diagnostic systems, leading to the development of the OBD2 standard. SAE standardized Diagnostic Trouble Codes (DTCs) and the physical OBD connector itself (SAE J1962), ensuring consistency across different vehicle manufacturers.

The adoption of OBD2 protocols expanded globally in stages:

1996: OBD2 became mandatory in the USA for all cars and light trucks.
2001: The European Union mandated OBD2 (EOBD) for gasoline cars.
2003: EOBD requirements extended to diesel cars in the EU.
2005: OBD2 was required in the US for medium-duty vehicles.
2008: US vehicles were mandated to use ISO 15765-4 (CAN bus) as the foundation for OBD2 protocols.
2010: OBD2 compliance became mandatory for heavy-duty vehicles in the US.

The Future of OBD2 Protocols: Trends and Innovations

While OBD2 protocols are well-established, the automotive landscape is evolving, leading to new trends and potential changes in how OBD2 is implemented and utilized.

Initially designed for emissions testing, legislated OBD2 faces challenges in the age of electric vehicles. Notably, electric vehicles are not legally bound to support OBD2 protocols in the same way as internal combustion engine vehicles. In practice, many modern EVs do not support standard OBD2 requests, opting instead for OEM-specific UDS (Unified Diagnostic Services) communication. This OEM-specific approach often makes accessing data from EVs challenging without reverse engineering the communication protocols. However, there are successful cases of reverse engineering and data access for brands like Tesla, Hyundai/Kia, Nissan, and VW/Skoda EVs.

Recognizing the limitations of current OBD2 implementations in terms of data richness and underlying protocols, advancements like WWH-OBD (World Wide Harmonized OBD) and OBDonUDS (OBD on UDS) have emerged. These aim to modernize OBD communication by using the UDS protocol as a foundation, offering improved efficiency and capabilities. For a deeper understanding of UDS, refer to our introduction to UDS.

The rise of connected cars and the need for remote diagnostics are pushing the evolution towards OBD3. OBD3 envisions incorporating telematics into vehicles, potentially adding a small radio transponder to transmit Vehicle Identification Numbers (VINs) and DTCs wirelessly to central servers for automated emission checks and diagnostics. Devices like the CANedge2 WiFi CAN logger and CANedge3 3G/4G CAN logger already facilitate data transfer via WiFi or cellular networks, paving the way for OBD3-like functionalities. However, concerns surrounding data privacy and surveillance pose political challenges to widespread OBD3 adoption.

Another significant trend is the automotive industry’s consideration of limiting third-party access to OBD2 data. Originally intended for repair shop diagnostics, OBD2 is now widely used by third-party services for data-driven applications. Some manufacturers are exploring the idea of restricting OBD2 functionality during driving, centralizing data collection instead. This approach, driven by security concerns and the desire to control automotive big data, could potentially disrupt the market for third-party OBD2-based services.

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Key OBD2 Protocol Standards

OBD2 protocols are built upon a layered communication model, similar to the 7-layer OSI model used in networking. Think of OBD2 as a “language” for diagnostics, while CAN bus acts as the “phone line” for communication. OBD2 protocols are comparable to other CAN-based higher-layer protocols like J1939, CANopen, and NMEA 2000.

OBD2 standards define various aspects, including the OBD2 connector, lower-layer communication protocols, and OBD2 Parameter IDs (PIDs). These standards are crucial for ensuring interoperability and consistent diagnostic access across different vehicles and tools.

The standardization landscape for OBD2 involves both SAE (primarily US standards) and ISO (international standards). Many SAE and ISO standards are technically equivalent, such as SAE J1979 and ISO 15031-5 (defining diagnostic services) and SAE J1962 and ISO 15031-3 (defining the OBD2 connector).

The OBD2 Connector: SAE J1962 Standard

The 16-pin OBD2 connector, standardized under SAE J1962 / ISO 15031-3, provides a standardized physical interface for accessing vehicle data. This connector, often called the Data Link Connector (DLC), is typically located within easy reach near the steering wheel, though it might be hidden behind a panel in some vehicles.

Key features of the OBD2 connector include:

Accessibility: Designed for easy access, usually near the steering wheel.
Pin 16: Provides battery power, often active even when the ignition is off, to power diagnostic tools.
Protocol-Dependent Pinout: The function of other pins varies based on the specific communication protocol used by the vehicle.
CAN Bus Integration: In vehicles using CAN bus as the lower-layer protocol (common in modern cars), pins 6 (CAN-High) and 14 (CAN-Low) are used for CAN communication.

OBD2 Connector Types: Type A vs. Type B

You may encounter two main types of OBD2 connectors: Type A and Type B. Type A is predominantly used in cars and light-duty vehicles, while Type B is more common in medium and heavy-duty vehicles.

While both types share a similar pin layout, they differ in:

Power Supply: Type A typically provides 12V power, while Type B provides 24V, reflecting the different electrical systems in cars versus larger vehicles.
Baud Rate: Cars often use a CAN bus baud rate of 500 kbps, whereas heavy-duty vehicles commonly use 250 kbps (though 500 kbps is increasingly supported).

Visually, Type B connectors have a distinguishing interrupted groove in the middle. This physical difference ensures that a Type B OBD2 adapter cable is compatible with both Type A and Type B sockets, while a Type A adapter will only fit into a Type A socket.

OBD2 Protocols and CAN Bus: ISO 15765-4

Since 2008, CAN bus has become the mandatory lower-layer protocol for OBD2 in all vehicles sold in the US, as specified by ISO 15765. This standard, formally known as ISO 15765-4 (Diagnostics over CAN or DoCAN), outlines specific constraints and guidelines for implementing OBD2 communication over a CAN network (ISO 11898).

ISO 15765-4 standardizes the CAN interface for diagnostic equipment at the physical, data link, and network layers, specifying:

CAN Bus Bit-rate: Must be either 250 kbps or 500 kbps.
CAN IDs: Supports both 11-bit (standard) and 29-bit (extended) CAN identifiers.
Specific CAN IDs for OBD2: Defines dedicated CAN IDs for OBD2 request and response messages.
Diagnostic CAN Frame Data Length: Mandates a data payload of 8 bytes per CAN frame.
OBD2 Adapter Cable Length: Limits the maximum length of the OBD2 adapter cable to 5 meters.

OBD2 CAN Identifiers: 11-bit and 29-bit

OBD2 communication over CAN bus relies on a request-response messaging system. Vehicles typically use either 11-bit or 29-bit CAN identifiers for these messages.

In most cars, 11-bit CAN IDs are used for OBD2 communication. The functional addressing ID 0x7DF is commonly used to send a request to all OBD2-compliant Electronic Control Units (ECUs). This ID essentially asks any ECU that has the requested data to respond. Physical addressing IDs in the range 0x7E0-0x7E7 can be used to target specific ECUs, although this is less common.

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

Some vehicles, particularly vans and medium to heavy-duty vehicles, may use 29-bit extended CAN identifiers for OBD2. In these cases, the functional addressing CAN ID is 0x18DB33F1. Responses are sent with CAN IDs ranging from 0x18DAF100 to 0x18DAF1FF, with common examples being 0x18DAF110 and 0x18DAF11E. These 29-bit IDs are sometimes represented in the J1939 PGN (Parameter Group Number) format, specifically PGN 0xDA00 (55808), which is reserved for ISO 15765-2 in the J1939-71 standard.

OBD2 Protocols vs. Proprietary CAN Protocols

It’s crucial to understand that a vehicle’s internal systems and Electronic Control Units (ECUs) operate using proprietary CAN protocols defined by the Original Equipment Manufacturer (OEM). OBD2 protocols are an additional layer built on top of these OEM-specific networks for diagnostic purposes. OEM protocols are highly specific to vehicle brand, model, and year and are generally not publicly documented. Interpreting this proprietary CAN data typically requires reverse engineering.

When you connect a CAN bus data logger to the OBD2 connector, you might observe both OEM-specific CAN data (often transmitted at high rates of 1000-2000 frames/second) and OBD2 communication. However, in many newer vehicles, a ‘gateway’ module might restrict access to the OEM CAN data through the OBD2 port, allowing only OBD2 communication.

In essence, OBD2 protocols function as a parallel, higher-layer communication system alongside the vehicle’s primary OEM-specific CAN network.

Bit-rate and CAN ID Validation for OBD2 Protocols

OBD2 protocols over CAN bus can utilize two bit-rates (250 kbps or 500 kbps) and two CAN ID lengths (11-bit or 29-bit), resulting in four potential protocol combinations. Modern vehicles commonly use 500 kbps with 11-bit IDs, but diagnostic tools should systematically validate the correct combination for each vehicle.

ISO 15765-4 provides a recommended initialization sequence to automatically determine the correct protocol combination. This process relies on the fact that OBD2-compliant vehicles must respond to a specific mandatory OBD2 request (related to OBD2 PIDs) and that using an incorrect bit-rate will generate CAN error frames, signaling a communication mismatch.

Newer versions of ISO 15765-4 also account for vehicles that might support OBD communication via OBDonUDS (OBD on Unified Diagnostic Services) instead of the more traditional OBDonEDS (OBD on Emission Diagnostic Services). While this article primarily focuses on OBD2/OBDonEDS (defined by ISO 15031-5/SAE J1979), WWH-OBD/OBDonUDS (defined by ISO 14229, ISO 27145-3/SAE J1979-2) is becoming increasingly relevant, especially in EU trucks and buses.

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

Currently, OBDonEDS (also known as OBD2, SAE OBD, EOBD, or ISO OBD) is prevalent in most non-electric vehicles, while WWH-OBD is mainly found in EU trucks and buses.

Alternative Lower-Layer OBD2 Protocols

While CAN bus (ISO 15765) is the dominant lower-layer protocol for OBD2 today, especially in vehicles manufactured after 2008, older vehicles might utilize one of four other lower-layer protocols. Understanding these alternatives is helpful when working with pre-2008 vehicles. The OBD2 connector pinout can sometimes provide clues about the protocol in use.

ISO 15765 (CAN bus): Mandatory in US cars from 2008 onwards and now the most common protocol.
ISO 14230-4 (KWP2000): Keyword Protocol 2000, prevalent in cars from 2003 onwards, especially in Asia.
ISO 9141-2: Used in European, Chrysler, and Asian cars from around 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.

ISO-TP: Transporting OBD2 Messages [ISO 15765-2]

OBD2 communication relies on the ISO-TP (ISO 15765-2) transport protocol to handle messages exceeding the 8-byte payload limit of a single CAN frame. ISO-TP is essential for transmitting larger OBD2 data like Vehicle Identification Numbers (VINs) or Diagnostic Trouble Codes (DTCs), which require segmentation, flow control, and reassembly of messages. For a detailed explanation of ISO-TP, refer to our introduction to UDS.

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. In a Single Frame, the first data byte (PCI field) indicates the payload length (excluding padding), leaving 7 bytes for OBD2-specific data.

Anatomy of an OBD2 Diagnostic Message: SAE J1979, ISO 15031-5

To understand OBD2 protocols at a deeper level, let’s examine the structure of a raw ‘Single Frame’ OBD2 CAN message. Simplified, an OBD2 message consists of a CAN identifier, a data length indicator (PCI field), and the data payload. The payload is further structured into:

Mode (Service): Defines the type of diagnostic request (e.g., request current data, request DTCs).
Parameter ID (PID): Specifies the particular parameter being requested within a given mode (e.g., vehicle speed, engine RPM).
Data Bytes: Contain the actual data related to the requested parameter.

OBD2 Request/Response Example: Vehicle Speed

Consider a practical example of requesting and receiving vehicle speed data using OBD2 protocols.

A diagnostic tool sends a request message with CAN ID 0x7DF and a 2-byte payload: Mode 0x01 (Show current data) and PID 0x0D (Vehicle Speed). The vehicle responds with a message on CAN ID 0x7E8 and a 3-byte payload. The vehicle speed value is encoded in the fourth data byte, which in this example is 0x32 (decimal 50).

By consulting the OBD2 PID specifications for PID 0x0D, we can determine that the value 0x32 represents a vehicle speed of 50 km/h. This demonstrates the fundamental request-response mechanism and data encoding within OBD2 protocols.

The 10 Standardized OBD2 Services (Modes)

OBD2 protocols define 10 standardized diagnostic services, also referred to as modes. Each mode corresponds to a specific category of diagnostic information or action.

Mode 0x01 (Show current data): Requests real-time sensor data and vehicle parameters.
Mode 0x02 (Show freeze frame data): Retrieves data captured when a DTC was set.
Mode 0x03 (Show stored DTCs): Requests currently active Diagnostic Trouble Codes.
Mode 0x04 (Clear DTCs): Clears stored DTCs and related diagnostic information.
Mode 0x05 (Oxygen sensor monitoring test results): Retrieves results from oxygen sensor tests.
Mode 0x06 (On-board monitoring test results for non-continuously monitored systems): Accesses test results for specific systems.
Mode 0x07 (Show pending DTCs): Requests DTCs that are not yet confirmed but have been detected.
Mode 0x08 (Control operation of on-board system, test or component): Allows for actuating certain vehicle components for testing.
Mode 0x09 (Request vehicle information): Used to request vehicle-specific information like VIN or calibration IDs.
Mode 0x0A (Show permanent DTCs): Retrieves DTCs that cannot be cleared by normal means.

It’s important to note that vehicles are not required to support all 10 OBD2 modes. Furthermore, manufacturers may implement additional, OEM-specific OBD2 modes beyond these standardized services.

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

OBD2 Parameter IDs (PIDs)

Within each OBD2 mode, Parameter IDs (PIDs) are used to specify the exact data being requested. For example, within Mode 0x01 (Show current data), there are approximately 200 standardized PIDs that represent various real-time parameters like vehicle speed, engine RPM, intake air temperature, and fuel level.

However, vehicles are not obligated to support all standardized PIDs within a given mode. In practice, most vehicles only support a subset of the available PIDs.

One PID holds special significance: 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 provides a bitmask indicating which PIDs in the range 0x01-0x20 it supports. This makes PID 0x00 a fundamental tool for verifying OBD2 compatibility and discovering supported PIDs. 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).

Practical Tip: OBD2 PID Overview Tool

The appendices of SAE J1979 and ISO 15031-5 contain detailed scaling and decoding information for standard OBD2 PIDs. This information is crucial for converting raw OBD2 data into meaningful physical values.

To simplify working with Mode 0x01 PIDs, we offer a free OBD2 PID overview tool. This tool helps you construct OBD2 request frames and dynamically decode OBD2 responses, streamlining the process of accessing and interpreting OBD2 data.

OBD2 PID overview tool

Logging and Decoding OBD2 Protocol Data: A Practical Guide

Let’s walk through a practical example of logging OBD2 data using a CANedge CAN bus data logger. The CANedge allows for custom CAN frame transmission, making it ideal for OBD2 data logging.

To connect the CANedge to your vehicle, use our OBD2-DB9 adapter cable.

You can send a CAN frame at e.g. 500K, then check if it is successfully sent

The responses to ‘Supported PIDs’ can be reviewed in asammdf

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

As per ISO 15765-4, the first step is to determine the correct bit-rate, CAN IDs, and supported PIDs for your specific vehicle. The CANedge can be configured to automate this process. Refer to the CANedge Intro for detailed configuration instructions. The general steps are:

Bit-rate Test: Send a CAN frame at 500 kbps and check for successful transmission. If unsuccessful, try 250 kbps.
Protocol Determination: Use the identified bit-rate for subsequent communication.
Supported PIDs Discovery: Send multiple ‘Supported PIDs’ requests (Mode 0x01 PID 0x00, 0x20, 0x40, etc.) and analyze the responses.
CAN ID Identification: Response IDs will indicate whether the vehicle uses 11-bit or 29-bit CAN IDs for OBD2.
PID Support Analysis: Examine the response data to determine the range of PIDs supported by the vehicle.

We provide plug-and-play CANedge configurations to streamline these initial tests. Most post-2008 non-EV cars typically support 40-80 PIDs using a 500 kbps bit-rate, 11-bit CAN IDs, and the OBD2/OBDonEDS protocol.

Analyzing the responses in software like asammdf GUI often reveals multiple responses to a single OBD2 request, especially when using the functional address ID 0x7DF. This is because the 0x7DF ID polls all OBD2-compliant ECUs. Since Mode 0x01 PID 0x00 is mandatory, multiple ECUs may respond. Note that the ECM (0x7E8) often supports all PIDs supported by other ECUs in the vehicle. To reduce bus load, consider using physical addressing (e.g., CAN ID 0x7E0) to target specific ECUs for subsequent requests.

Step #2: Configure OBD2 PID Requests for Logging

Once you have identified the supported PIDs, bit-rate, and CAN IDs, configure your CANedge to transmit requests for the PIDs you wish to log. Consider these best practices:

Physical Addressing: Use physical addressing request IDs (e.g., 0x7E0) to minimize redundant responses and bus traffic.
Request Spacing: Introduce a delay of 300-500 ms between consecutive OBD2 requests. Aggressive polling can overwhelm ECUs and lead to dropped responses.
Power Management: Implement triggers to stop OBD2 requests when the vehicle is inactive to prevent battery drain, especially if the CANedge remains connected when the vehicle is off.
Data Filtering: Apply filters to record only OBD2 response messages, especially if the vehicle also broadcasts OEM-specific CAN data, to keep log files focused and efficient.

With these configurations in place, your CANedge is ready to log raw OBD2 data directly from your vehicle!

An example list of CANedge OBD2 PID requests

asammdf lets you DBC decode and visualize OBD2 data

Step #3: DBC Decode Raw OBD2 Data for Analysis

To analyze and visualize your logged OBD2 data, you need to convert the raw data into human-readable physical values (e.g., km/h, °C, RPM). This decoding process uses information from ISO 15031-5/SAE J1979 and publicly available resources like Wikipedia.

For convenience, we provide a free OBD2 DBC file that simplifies DBC decoding of raw OBD2 data in most CAN bus software tools. OBD2 DBC file

Decoding OBD2 data is more complex than standard CAN signal decoding. Different OBD2 PIDs are transmitted using the same CAN ID (e.g., 0x7E8). Therefore, the CAN ID alone is insufficient to identify the signals within the payload.

OBD2 decoding requires considering the CAN ID, OBD2 mode, and OBD2 PID to correctly identify and interpret the signals. This technique is known as ‘extended multiplexing‘ and can be implemented in DBC files to handle the multi-layered decoding logic.

CANedge: Your OBD2 Data Logging Solution

The CANedge provides a user-friendly solution for recording OBD2 data to SD cards (8-32 GB). Simply connect the CANedge to your vehicle’s OBD2 port to start logging. Utilize our free software and APIs and the OBD2 DBC file for efficient data analysis and visualization.

OBD2 logger intro

CANedge

OBD2 Multi-Frame Communication Examples: ISO-TP in Action

While many OBD2 interactions are single-frame, some operations require multi-frame communication using ISO-TP (ISO 15765-2) to transmit larger payloads. Multi-frame communication involves flow control frames to manage data segmentation and reassembly. Diagnostic tools and CAN software that support ISO-TP, like the CANedge MF4 decoders, are needed to handle these complex exchanges.

Example 1: Requesting the Vehicle Identification Number (VIN) via OBD2

Retrieving the Vehicle Identification Number (VIN) is a common task in telematics and diagnostics. OBD2 Mode 0x09 PID 0x02 is used to request the VIN.

The diagnostic tool initiates the request with a Single Frame message containing the PCI field (0x02), request service ID (0x09), and PID (0x02).

The vehicle responds with a multi-frame response, starting with a First Frame. This frame includes the PCI, total message length (0x014 = 20 bytes), mode (0x49, which is 0x09 + 0x40), and PID (0x02). Following the PID, the Number Of Data Items (NODI) byte (0x01 in this case) indicates that there is one data item (the VIN). The subsequent 17 bytes contain the VIN itself, encoded in HEX, which can be converted to ASCII to obtain the human-readable VIN string.

Example 2: Multi-PID Request (6 PIDs in one request)

OBD2 protocols allow requesting up to 6 Mode 0x01 PIDs in a single request frame. The ECU will respond with data for the supported PIDs in the request, potentially using multi-frame responses if the data exceeds a single CAN frame. This method can improve data acquisition efficiency but introduces complexities in data decoding and standardization. Therefore, it is generally not recommended for practical data logging unless you have specialized tools and decoding solutions.

The multi-frame response format is similar to the VIN example, but the payload includes the requested PIDs themselves, followed by the corresponding data for each PID. The PIDs in the response are often ordered as they were requested, but this is not strictly mandated by the ISO 15031-5 standard.

Decoding multi-PID responses using generic DBC files is challenging due to the variable payload structure and PID ordering. Custom decoding scripts and specialized tools are often needed to reliably process this type of data.

Example 3: Requesting Diagnostic Trouble Codes (DTCs) via OBD2

OBD2 Mode 0x03, “Show stored Diagnostic Trouble Codes,” is used to retrieve emissions-related DTCs. The request frame for Mode 0x03 does not include a PID. The responding ECU(s) will indicate the number of stored DTCs (which could be zero) and then transmit the DTCs, with each DTC occupying 2 bytes. Multi-frame responses are necessary when more than two DTCs are stored.

The 2-byte DTC value is structured according to ISO 15031-5/ISO 15031-6. The first two bits define the DTC category (e.g., Powertrain, Body, Chassis, Network), and the remaining 14 bits represent a 4-digit code (displayed in hexadecimal). Online OBD2 DTC lookup tools, like repairpal.com, can be used to decode these DTC values into descriptive error messages.

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

Real-World Use Cases for OBD2 Protocol Data Logging

OBD2 data logging from cars and light trucks has diverse applications across various industries:

Vehicle Data Logging for Cars:

OBD2 data can be leveraged for various purposes, including fuel efficiency optimization, driver behavior analysis, prototype testing, and insurance telematics.

obd2 logger

Real-time Vehicle Diagnostics:

OBD2 interfaces enable real-time streaming of diagnostic data for immediate vehicle health assessments and troubleshooting.

obd2 streaming

Predictive Maintenance for Fleets:

IoT-enabled OBD2 loggers can monitor vehicle fleets in the cloud, enabling predictive maintenance strategies to minimize downtime and prevent breakdowns.

predictive maintenance

Vehicle Black Box Recording:

OBD2 loggers can serve as ‘black boxes’ in vehicles and equipment, providing crucial data for accident reconstruction, dispute resolution, and diagnostic analysis.

can bus blackbox

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

Explore our guides section for more introductory articles or download our comprehensive ‘Ultimate Guide’ PDF for in-depth knowledge. Ultimate Guide

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