Understanding OBD2 Live Data: The Expert Guide & PDF

Want to truly understand your car’s health through OBD2 live data?

This comprehensive guide dives deep into the world of On-Board Diagnostics II (OBD2) live data. We’ll break down everything from the OBD2 connector and Parameter IDs (PIDs) to practical applications and how to access and interpret this valuable information. Whether you’re a seasoned mechanic or a curious car owner, this guide will empower you to effectively use OBD2 live data for diagnostics and performance monitoring.

For easy offline access, we also offer this guide in PDF format, perfect for workshops and on-the-go learning.

What is OBD2 Live Data?

OBD2 Live Data refers to the stream of real-time information broadcast by your vehicle’s computer system. This data, accessible through the standardized OBD2 port, provides a window into your car’s operational status. It includes crucial parameters like engine speed (RPM), coolant temperature, oxygen sensor readings, fuel trim, and much more.

Think of it as a live health monitor for your car. Just like a doctor uses vital signs to assess a patient, mechanics and car enthusiasts use OBD2 live data to understand a vehicle’s condition in real-time. This dynamic data stream is invaluable for:

Diagnosing Issues: Identifying the root cause of problems, often before they escalate into costly repairs.
Performance Monitoring: Tracking engine performance, fuel efficiency, and other key metrics.
Preventive Maintenance: Spotting potential issues early, allowing for timely maintenance and preventing breakdowns.
Vehicle Health Checks: Gaining a comprehensive understanding of your car’s overall health.

You’ve likely already encountered the OBD2 system through the “check engine light” or Malfunction Indicator Light (MIL) on your dashboard. This light signals that your car’s self-diagnostic system has detected an issue. Mechanics utilize OBD2 scanners to retrieve Diagnostic Trouble Codes (DTCs) and, crucially, analyze OBD2 live data to pinpoint the problem.

Alt text: OBD2 system interface with malfunction indicator light and scan tool displayed, illustrating on-board diagnostics.

By connecting an OBD2 reader to the 16-pin OBD2 connector, typically located near the steering wheel, you can tap into this wealth of real-time data. The scanner sends requests, and your car responds with data packets containing parameters like speed, fuel level, and DTCs, enabling efficient and accurate troubleshooting.

Is OBD2 Live Data Available for My Car?

The answer is almost certainly yes, especially if you own a non-electric vehicle manufactured in recent decades.

OBD2 has become a globally adopted standard. For gasoline cars in the US, OBD2 became mandatory in 1996, and for light trucks in the same year. The European Union followed suit, requiring OBD2 for gasoline cars in 2001 and diesel cars in 2003 (EOBD). By 2008, the US mandated ISO 15765-4 (CAN) as the foundation for OBD2 in all cars.

While most modern cars are OBD2 compliant, older vehicles with a 16-pin connector might not fully support the OBD2 protocol. To confirm OBD2 compliance, consider the vehicle’s origin and purchase date:

Does My Car Have OBD2?
Alt text: OBD2 compliance timeline chart for US and EU regions, illustrating vehicle age and regulatory compliance.

OBD2 Compliance Timeline:

USA:
- 1996: Mandatory for cars and light trucks
- 2005: Required for medium-duty vehicles
- 2010: Required for heavy-duty vehicles
EU:
- 2001: Required for gasoline cars (EOBD)
- 2003: Required for diesel cars (EOBD)

A Brief History of OBD2 and its Evolution

The story of OBD2 begins in California. The California Air Resources Board (CARB) pioneered the concept, mandating OBD systems in all new cars from 1991 onwards to monitor and control vehicle emissions.

The Society of Automotive Engineers (SAE) played a pivotal role in standardizing OBD, leading to the OBD2 standard. This standardization included Diagnostic Trouble Codes (DTCs) and the OBD connector itself, ensuring consistency across different vehicle manufacturers (SAE J1962).

The OBD2 standard’s rollout was gradual but impactful:

1991: OBD mandated in California for emission control.
1996: OBD2 mandatory in the USA for cars and light trucks.
2001: OBD2 required in the EU for gasoline vehicles.
2003: OBD2 extended to diesel vehicles in the EU (EOBD).
2005: OBD2 became mandatory for medium-duty vehicles in the US.
2008: US vehicles must use ISO 15765-4 (CAN) as the OBD2 communication basis.
2010: OBD2 required for heavy-duty vehicles in the US.

Alt text: OBD2 history infographic highlighting emission control, exhaust regulations, and the role of CAN bus in data communication.

Alt text: OBD2 history timeline diagram showcasing the evolution of on-board diagnostics from inception to standardization.

Alt text: OBD3 future concept art depicting remote diagnostics, emissions testing, cloud connectivity, and IoT integration for vehicles.

The Future of OBD2: Trends and Challenges

While OBD2 remains relevant, the automotive landscape is evolving rapidly, leading to shifts in how OBD2 is implemented and utilized.

Originally designed for emission control, legislated OBD2 faces new challenges with the rise of electric vehicles (EVs). Interestingly, EVs are not mandated to support OBD2 in its traditional form. Many modern EVs largely bypass standard OBD2 requests, opting for OEM-specific UDS communication. This OEM-specific approach can make accessing EV data challenging without reverse engineering efforts. However, there are successful cases of reverse engineering and data access for brands like Tesla, Hyundai/Kia, Nissan, and VW/Skoda, as detailed in case studies focusing on electric car data analysis.

To address the limitations of OBD2 in terms of data richness and lower-layer protocols, newer standards have emerged, including WWH-OBD (World Wide Harmonized OBD) and OBDonUDS (OBD on UDS). These protocols aim to modernize OBD communication by using the UDS protocol as a foundation. For a deeper understanding of these advancements, resources on the UDS protocol are available.

In the age of connected cars, traditional OBD2 testing methods can seem outdated. Manual emission checks are time-consuming and costly. OBD3 proposes a solution: integrating telematics into all vehicles.

OBD3 envisions adding a small radio transponder to cars, enabling wireless transmission of the Vehicle Identification Number (VIN) and DTCs to a central server for automated checks. Technologies like WiFi and cellular data transfer, already utilized in devices like the CANedge2 WiFi CAN logger and CANedge3 3G/4G CAN logger, can facilitate this.

While OBD3 offers convenience and cost savings, it also raises privacy concerns related to vehicle surveillance, creating political and social challenges.

Furthermore, the intended use of OBD2 is shifting. Originally designed for stationary emission controls in repair shops, OBD2 is now extensively used by third parties to generate real-time data through OBD2 dongles, CAN loggers, and similar devices. This trend has sparked debate within the automotive industry. Concerns have been raised by manufacturers, particularly in Germany, about third-party access to vehicle data through OBD2. The argument is that OBD2 was not intended to enable a data-driven economy for external entities, and proposals to “turn off” OBD2 functionality during driving are being considered. This would centralize data collection with manufacturers, potentially giving them control over “automotive big data”.

While framed as a security measure to reduce car hacking risks, many perceive this shift as a commercially motivated move to control data access and potentially disrupt the market for third-party OBD2 services. The future direction of OBD2 and data access remains uncertain and is a topic of ongoing discussion.

Alt text: OBD2 connector removal illustration in an electric vehicle context, symbolizing restricted data access in EVs.

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Understanding OBD2 Standards: A Layered Approach

On-board diagnostics, OBD2, operates as a higher-layer protocol – essentially a language for communication. CAN bus, in contrast, is the communication method, akin to a phone line. This places OBD2 alongside other CAN-based higher-layer protocols like J1939, CANopen, and NMEA 2000.

OBD2 standards comprehensively define the OBD2 connector, lower-layer protocols, OBD2 Parameter IDs (PIDs), and other critical aspects of the system.

To visualize these standards, we can use the 7-layer OSI model. The following sections will focus on the most relevant standards within this model.

Notice that both SAE (Society of Automotive Engineers) and ISO (International Organization for Standardization) standards cover multiple layers. This reflects the development of OBD standards in both the USA (SAE) and EU (ISO). Many of these standards are technically very similar, for example, SAE J1979 and ISO 15031-5, and SAE J1962 and ISO 15031-3.

Alt text: OBD2 and CAN Bus OSI 7-layer model diagram, highlighting ISO 15765 and ISO 11898 standards across different layers.

The OBD2 Connector: Physical Interface to Live Data [SAE J1962]

The 16-pin OBD2 connector is your physical gateway to accessing your vehicle’s data. Specified in the SAE J1962 / ISO 15031-3 standard, this connector provides a standardized interface for diagnostic tools and data loggers.

The illustration below shows a typical Type A OBD2 pin connector, also known as a Data Link Connector (DLC).

Alt text: OBD2 connector pinout diagram, Type A female socket DLC, illustrating pin assignments for data communication.

Key points about the OBD2 connector:

Location: Usually found near the steering wheel, but its exact location can sometimes be hidden.
Pin 16: Provides battery power, often even when the ignition is off.
Pinout Variability: The specific pinout configuration depends on the communication protocol used by the vehicle.
CAN Bus Dominance: CAN bus is the most prevalent lower-layer protocol, meaning pins 6 (CAN-H) and 14 (CAN-L) are commonly used for data transmission.

OBD2 Connector Types: A vs. B

In practice, you might encounter both Type A and Type B OBD2 connectors. Type A is commonly found in cars, while Type B is more prevalent in medium and heavy-duty vehicles.

While both types share similar pinouts, they differ primarily in power supply output (12V for Type A, 24V for Type B) and often baud rates (500K for cars, 250K or 500K for heavy-duty vehicles).

Visually, a Type B OBD2 connector can be identified by an interrupted groove in the middle of the connector. This physical difference means that a Type B OBD2 adapter cable is generally compatible with both Type A and Type B sockets, while a Type A adapter might not fit into a Type B socket.

Alt text: OBD2 Connector Type A versus Type B comparison, highlighting SAE J1962 standards, voltage differences for car, van, and truck applications.

OBD2 Communication over CAN Bus [ISO 15765-4]

Since 2008, CAN bus has been the mandatory lower-layer protocol for OBD2 in all US vehicles, as defined by ISO 15765.

ISO 15765-4, also known as Diagnostics over CAN (DoCAN), builds upon the CAN standard (ISO 11898) by adding specific constraints for diagnostic communication.

Key ISO 15765-4 specifications for OBD2 over CAN:

Bit-rate: Must be either 250K or 500K.
CAN IDs: Supports both 11-bit and 29-bit CAN identifiers.
Specific CAN IDs: Defines specific CAN IDs for OBD requests and responses.
Data Length: Diagnostic CAN frames must have a data length of 8 bytes.
Cable Length: OBD2 adapter cables are limited to a maximum length of 5 meters.

Alt text: OBD2 versus CAN bus relationship diagram, emphasizing ISO15765 standard for diagnostics over CAN.

OBD2 CAN Identifiers: 11-bit and 29-bit

OBD2 communication relies on a request-response message structure.

In most passenger cars, 11-bit CAN IDs are used for OBD2. The ‘Functional Addressing’ ID, 0x7DF, is used to query all OBD2-compatible Electronic Control Units (ECUs) for data related to the requested parameter (as per ISO 15765-4). ‘Physical Addressing’ requests, using CAN IDs 0x7E0-0x7E7, target specific ECUs but are less commonly used.

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

Some vehicles, particularly vans and medium/heavy-duty vehicles, might use extended 29-bit CAN identifiers for OBD2 communication.

In 29-bit implementations, the ‘Functional Addressing’ CAN ID is 0x18DB33F1.

Responses in 29-bit systems use CAN IDs ranging from 0x18DAF100 to 0x18DAF1FF, with common IDs being 0x18DAF110 and 0x18DAF11E. These response IDs are sometimes represented in the J1939 PGN (Parameter Group Number) format, specifically PGN 0xDA00 (55808), which is designated as ‘Reserved for ISO 15765-2’ in the J1939-71 standard.

Alt text: OBD2 protocol request and response frame diagram, illustrating PID data parameter exchange.

OBD2 OBD CAN bus Identifiers 7DF 7E8 7E0

OBD2 vs. OEM-Specific CAN Protocols: Understanding the Difference

It’s crucial to understand that your vehicle’s ECUs operate using proprietary CAN protocols developed by the Original Equipment Manufacturer (OEM), independent of OBD2. These OEM-specific protocols are essential for the car’s core functions and can vary significantly between brands, models, and years. Unless you have OEM documentation or can successfully reverse engineer these protocols, interpreting this raw CAN data is usually not possible. Tools and techniques for CAN bus reverse engineering are available for those who wish to delve deeper.

When you connect a CAN bus data logger to your OBD2 port, you might see this OEM-specific CAN data, typically broadcast at high frequencies (1000-2000 frames/second). However, many newer vehicles incorporate a ‘gateway’ module that filters CAN traffic through the OBD2 port, allowing only OBD2 communication and blocking access to the underlying OEM-specific CAN data.

Think of OBD2 as a secondary, standardized communication layer that exists alongside and separate from the OEM’s primary CAN communication network.

Alt text: OBD2 versus proprietary CAN bus data comparison, highlighting the distinction between standardized OBD2 and OEM-specific data.

Bit-rate and ID Validation: Ensuring Correct Communication

OBD2 over CAN can utilize 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, but diagnostic tools should systematically verify the correct combination for each vehicle.

ISO 15765-4 provides a recommended initialization sequence to automatically determine the correct bit-rate and CAN ID configuration. This process leverages the fact that OBD2-compliant vehicles must respond to a specific mandatory OBD2 request (detailed in the OBD2 PID section) and that using 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) instead of the more traditional OBDonEDS (OBD on Emission Diagnostic Service). This article primarily focuses on OBDonEDS (OBD2, SAE OBD, EOBD, ISO OBD) as defined by ISO 15031-5/SAE J1979, in contrast to WWH-OBD/OBDonUDS (OBD on Unified Diagnostic Service) as per ISO 14229, ISO 27145-3/SAE J1979-2.

To detect whether a vehicle uses OBDonEDS or OBDonUDS, diagnostic tools can send additional UDS requests with 11-bit/29-bit functional address IDs for service 0x22 and Data Identifier (DID) 0xF810 (protocol identification). Vehicles supporting OBDonUDS must have ECUs that respond to this DID.

Currently, OBDonEDS is the prevalent protocol in most non-electric vehicles, while WWH-OBD is mainly used in EU trucks and buses.

Alt text: OBD2 bit-rate and CAN ID validation flowchart, illustrating ISO 15765-4 compliant process for communication parameter validation.

Five Lower-Layer OBD2 Protocols: Beyond CAN

While CAN bus (ISO 15765) is now the dominant lower-layer protocol for OBD2, particularly in vehicles from 2008 onwards, older cars might utilize one of four other protocols. Understanding these legacy protocols and their corresponding OBD2 connector pinouts can be helpful when working with older vehicles.

Alt text: OBD2 five protocol standards diagram, including CAN ISO 15765, KWP2000, SAE J1850, and ISO9141, highlighting protocol diversity.

Five Lower-Layer OBD2 Protocols:

ISO 15765 (CAN bus): Mandatory in US cars since 2008 and widely used today.
ISO 14230-4 (KWP2000): Keyword Protocol 2000, common in 2003+ vehicles, especially in Asia.
ISO 9141-2: Used in EU, Chrysler, and Asian cars during 2000-2004.
SAE J1850 (VPW): Primarily used in older General Motors (GM) vehicles.
SAE J1850 (PWM): Primarily used in older Ford vehicles.

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

All OBD2 data exchange over CAN bus relies on the ISO-TP (ISO 15765-2) transport protocol. ISO-TP enables the transmission of data payloads exceeding the 8-byte limit of a standard CAN frame. This is essential for OBD2 operations like retrieving the Vehicle Identification Number (VIN) or Diagnostic Trouble Codes (DTCs), which often require larger data packets. ISO-TP handles segmentation, flow control, and reassembly of these larger messages. More details on ISO-TP can be found in resources explaining the UDS protocol.

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 the actual OBD2 communication.

Alt text: ISO 15765-2 ISO-TP OBD2 frame types diagram, illustrating Single Frame, First Frame, Consecutive Frame, and Flow Control Frame.

Decoding the OBD2 Diagnostic Message [SAE J1979, ISO 15031-5]

To understand OBD2 communication at the message level, let’s examine a raw ‘Single Frame’ OBD2 CAN message. In its simplest form, an OBD2 message comprises a CAN identifier, a data length indicator (PCI field), and the data payload. The payload is further structured into Mode, Parameter ID (PID), and data bytes.

Alt text: OBD2 PIDs message structure breakdown, explaining OBD-II frame components like Mode, PID, ID, and data bytes.

Example: OBD2 Request and Response for Vehicle Speed

Consider a practical example: requesting and receiving vehicle speed data.

A diagnostic tool sends a request message with CAN ID 0x7DF and a 2-byte payload: Mode 0x01 and PID 0x0D. Mode 0x01 signifies “Show current data,” and PID 0x0D specifically requests “Vehicle Speed.”

The vehicle responds with a message using CAN ID 0x7E8 and a 3-byte payload. This payload includes the response to Mode 0x01 (indicated by 0x41, which is 0x01 + 0x40) and the vehicle speed value in the 4th byte, in this case, 0x32 (decimal 50).

By consulting the OBD2 PID documentation for PID 0x0D, we find that the value 0x32 represents a vehicle speed of 50 km/h. This process of converting raw data bytes into meaningful physical values is crucial for interpreting OBD2 live data.

Alt text: OBD2 request 7DF and response 7E8 sequence diagram, illustrating PID communication for vehicle speed retrieval.

Alt text: OBD2 PID example for Vehicle Speed 0D, detailing the parameter identification for speed data.

The 10 Standard OBD2 Services (Modes)

OBD2 defines 10 diagnostic services, often referred to as modes. Mode 0x01 is used to access current real-time data, while other modes handle functions like retrieving and clearing Diagnostic Trouble Codes (DTCs) or accessing freeze frame data (snapshots of data captured when a DTC was set).

Not all OBD2 modes are mandatory for vehicle manufacturers to implement. Vehicles may also support OEM-specific modes beyond the 10 standardized modes.

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

Alt text: OBD2 services modes diagram, outlining 10 PID modes for diagnostic services including current data, freeze frame, and DTC clearing.

OBD2 Parameter IDs (PIDs): Accessing Specific Data Points

Within each OBD2 mode, Parameter IDs (PIDs) are used to request specific data points.

For instance, Mode 0x01 contains approximately 200 standardized PIDs providing real-time data on parameters like vehicle speed, engine RPM, and fuel level. However, vehicles are not required to support all PIDs within a given mode. In practice, most vehicles support only a subset of the available PIDs.

One PID holds special significance:

Mode 0x01 PID 0x00 is mandatory for all emissions-related ECUs that support any OBD2 services. When queried with PID 0x00, the ECU responds with a bitmask indicating which PIDs in the range 0x01-0x20 it supports. This makes PID 0x00 a fundamental tool for testing OBD2 compatibility and discovering supported PIDs. Similarly, PIDs 0x20, 0x40, 0x60, 0x80, 0xA0, and 0xC0 can be used to determine support for subsequent ranges of Mode 0x01 PIDs.

Alt text: OBD2 protocol request and response frames, reinforcing PID data parameter communication flow.

OBD2 PID overview tool
Alt text: OBD2 PID overview tool interface screenshot, showcasing service 01 for parameter identification and data access.

Tip: Utilizing an OBD2 PID Overview Tool

SAE J1979 and ISO 15031-5 appendices detail the scaling and conversion formulas for standard OBD2 PIDs, enabling you to translate raw data bytes into physical values.

For quick lookup of Mode 0x01 PIDs, consider using an online OBD2 PID overview tool. These tools can assist in constructing OBD2 request frames and dynamically decoding OBD2 responses. Our free OBD2 PID overview tool is readily available.

OBD2 PID overview tool

Practical Guide: Logging and Decoding OBD2 Live Data

Let’s walk through a practical example of logging OBD2 live data using the CANedge CAN bus data logger.

The CANedge allows you to define custom CAN frames for transmission, making it ideal for sending OBD2 requests and logging responses.

Once configured, the CANedge can be easily connected to your vehicle’s OBD2 port using an OBD2-DB9 adapter cable.

Alt text: OBD2 PID data logger setup diagram, illustrating request 7DF and response 7E8 in a data logging scenario.

OBD2 bit rate test You can send a CAN frame at e.g. 500K, then check if it is successfully sent

OBD2 Supported PIDs Test The responses to ‘Supported PIDs’ can be reviewed in asammdf

Review supported PIDs via OBD2 lookup tool
Alt text: OBD2 supported PIDs review via lookup tool, demonstrating PID result decoding.

Step #1: Bit-rate, ID, and Supported PID Validation

As previously discussed, ISO 15765-4 outlines a process for determining the correct bit-rate and CAN IDs for a specific vehicle. You can use the CANedge to perform these tests:

Bit-rate Test: Send a CAN frame at 500K. If successful, proceed. If not, try 250K.
Bit-rate Confirmation: Use the successfully tested bit-rate for subsequent communication.
Supported PID Discovery: Send multiple ‘Supported PIDs’ requests (Mode 0x01 PID 0x00 and subsequent range PIDs) and analyze the responses.
ID Type Determination: Based on the response IDs (0x7E8-0x7EF for 11-bit, 0x18DAF100-0x18DAF1FF for 29-bit), determine the CAN ID length used by the vehicle.
Supported PID Identification: Analyze the response data to identify the specific PIDs supported by the vehicle.

We provide plug-and-play CANedge configuration files to simplify these initial tests.

Most non-EV cars manufactured from 2008 onwards 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, multiple ECUs may respond to a single OBD request, particularly when using the functional address 0x7DF, which queries all ECUs. Since Mode 0x01 PID 0x00 is mandatory for OBD2-compliant ECUs, many ECUs often respond to this request. For subsequent ‘Supported PIDs’ requests, fewer ECUs tend to respond. Notably, the ECM (0x7E8) often supports all PIDs supported by other ECUs in the vehicle. Therefore, to reduce bus load, you can switch to ‘Physical Addressing’ using CAN ID 0x7E0 to target the ECM specifically for subsequent requests.

Step #2: Configuring OBD2 PID Requests for Logging

Once you’ve identified the supported PIDs, bit-rate, and CAN IDs for your vehicle, you can configure the CANedge to request specific PIDs for data logging.

Configuration considerations:

CAN IDs: Switch to ‘Physical Addressing’ request IDs (e.g., 0x7E0) to minimize redundant responses.
Request Spacing: Introduce a delay of 300-500 ms between OBD2 requests to prevent overwhelming ECUs.
Power Management: Implement triggers to stop data transmission when the vehicle is inactive to avoid battery drain.
Data Filtering: Set up filters to record only OBD2 responses, especially if your vehicle also outputs OEM-specific CAN data.

With these configurations in place, your CANedge is ready to log raw OBD2 live data.

obd2-transmit-list-example-canedge An example list of CANedge OBD2 PID requests

OBD2 data decoded visual plot asammdf CAN bus DBC file asammdf lets you DBC decode and visualize OBD2 data

Step #3: DBC Decoding of Raw OBD2 Data

To analyze and visualize your logged OBD2 data, you need to decode the raw data bytes into meaningful physical values.

Decoding information is available in ISO 15031-5/SAE J1979 and online resources like Wikipedia. For convenience, we offer a free OBD2 DBC file to simplify DBC decoding in most CAN bus analysis software tools.

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

To correctly decode OBD2 data, you must consider the CAN ID, OBD2 mode, and OBD2 PID together. This multiplexing technique, known as ‘extended multiplexing‘, can be effectively implemented using DBC files.

CANedge: Your OBD2 Live Data Logging Solution

The CANedge provides an easy and efficient way to record OBD2 live data onto an 8-32 GB SD card. Simply connect the CANedge to your vehicle’s OBD2 port to start logging. Analyze and decode your data using our free software and APIs and our OBD2 DBC file.

OBD2 logger intro
CANedge

OBD2 Multi-Frame Examples: Handling Larger Data Sets [ISO-TP]

OBD2 communication, as mandated by ISO 15765-2, utilizes the ISO-TP transport protocol for all data exchange. While many examples involve single-frame messages, multi-frame communication is necessary for larger data sets.

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, as demonstrated 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-message-vehicle-identification-number
Alt text: OBD2 multi-frame request message example for Vehicle Identification Number retrieval, showcasing ISO-TP communication.

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

The Vehicle Identification Number (VIN) is essential for telematics, diagnostics, and vehicle identification. To retrieve the VIN using OBD2, you use Mode 0x09 and PID 0x02.

VIN Vehicle Identification Number OBD2 Example multi-frame

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

The vehicle responds with a First Frame containing PCI, total message length (0x014 = 20 bytes), mode (0x49 = 0x09 + 0x40), and PID (0x02). Following the PID is the Number Of Data Items (NODI) byte (0x01, indicating one VIN). The subsequent 17 bytes contain the VIN itself, which can be converted from HEX to ASCII characters.

Example 2: Multi-PID Request (6x PIDs)

OBD2 allows diagnostic tools to request up to six Mode 0x01 PIDs in a single request frame. The ECU will respond with data for the supported PIDs from the request, omitting data for unsupported PIDs. If necessary, the response may span multiple frames using ISO-TP.

This multi-PID request feature can increase data acquisition efficiency but introduces complexities in data decoding. The signal encoding becomes specific to the request method, making generic OBD2 DBC files less suitable for decoding. We generally advise against using multi-PID requests for practical data logging due to these complexities. However, for illustrative purposes, an example trace is shown below:

Requesting multiple PIDs in one request

The multi-frame response structure is similar to the VIN example, but the payload includes both the requested PIDs and their corresponding data values. The PIDs are often ordered in the response similar to their order in the request, but this is not strictly mandated by ISO 15031-5.

Decoding multi-PID responses using generic DBC files is challenging due to the complex multiplexing. Custom scripts and tools that correlate request and response messages may be necessary for reliable decoding.

Example 3: Retrieving Diagnostic Trouble Codes (DTCs)

OBD2 Mode 0x03, “Show stored Diagnostic Trouble Codes,” is used to request emissions-related DTCs. No PID is included in the request. The ECU responds with the number of stored DTCs (which can be zero) and the DTC codes themselves. Each DTC is represented by 2 data bytes. Multi-frame responses are required 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 indicate the DTC category, and the remaining 14 bits form a 4-digit hexadecimal code. Decoded DTC values can be looked up using online OBD2 DTC lookup tools.

The example below shows a request to an ECU with 6 stored DTCs.

Alt text: OBD2 DTC Diagnostic Trouble Code DBC interpretation example, detailing DTC decoding process and structure.

OBD2 Diagnostic Trouble Codes DTC CAN Bus Request Response Example

Real-World Applications of OBD2 Live Data Logging

OBD2 live data from cars and light trucks has diverse applications:

Alt text: OBD2 data logger application in on-board diagnostics, visualizing data logging in a car.

Vehicle Data Logging for Cars

OBD2 data logging in cars can be used for:

Fuel Efficiency Optimization: Analyzing driving habits and vehicle parameters to reduce fuel consumption.
Driving Behavior Improvement: Monitoring driving patterns to promote safer and more efficient driving.
Prototype Testing: Validating and testing new automotive components and systems.
Insurance Telematics: Providing data for usage-based insurance models.

obd2 logger

Alt text: OBD2 real-time streaming diagnostics via USB, illustrating live data streaming for vehicle diagnostics.

Real-time Car Diagnostics

OBD2 interfaces enable real-time streaming of human-readable OBD2 data, facilitating:

Vehicle Issue Diagnosis: Quickly identifying and diagnosing vehicle malfunctions.
Live Parameter Monitoring: Observing critical vehicle parameters in real-time for troubleshooting.

obd2 streaming

Alt text: OBD2 data logger for predictive maintenance, depicting telematics and IoT integration for preventive car care.

Predictive Maintenance for Vehicles

Cloud-connected IoT OBD2 loggers enable:

Remote Vehicle Monitoring: Tracking vehicle health remotely.
Predictive Maintenance: Analyzing data to predict potential breakdowns and schedule preventative maintenance.

predictive maintenance

Alt text: Black box CAN logger for insurance and warranty, visualizing data logging for vehicle event recording.

Vehicle Black Box Functionality

OBD2 loggers can serve as vehicle “black boxes”:

Event Recording: Capturing vehicle data during events like accidents or malfunctions.
Dispute Resolution: Providing objective data for accident investigations or warranty claims.
Diagnostic Data Logging: Recording data for in-depth diagnostics and troubleshooting.

can bus blackbox

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

Explore our extensive guides section for more in-depth introductions to CAN bus and related technologies, or download our ‘Ultimate Guide’ in PDF format.

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