Understanding the CAN Bus to OBD2 Adapter: Your Guide to Vehicle Diagnostics

Need a straightforward guide to Can Bus To Obd2 Adapters? You’ve come to the right place.

This article will demystify the CAN bus to OBD2 adapter, explaining its crucial role in modern vehicle diagnostics. We’ll explore the OBD2 protocol, the CAN bus system, and how these adapters bridge the gap between them, enabling access to valuable vehicle data.

Whether you’re a seasoned mechanic or a car enthusiast, understanding the CAN bus to OBD2 adapter is essential in today’s automotive landscape. This guide will provide you with the knowledge to effectively utilize these adapters for diagnostics, data logging, and more.

You can also explore our comprehensive resources on vehicle networking protocols for deeper insights.

What is OBD2 and Why is CAN Bus Important?

OBD2 (On-Board Diagnostics II) is your car’s built-in diagnostic system. It’s a standardized protocol that allows you to retrieve diagnostic trouble codes (DTCs) and real-time data from your vehicle through the OBD2 connector. This standardization is critical for mechanics and vehicle owners alike, enabling efficient troubleshooting and maintenance.

You’re likely already familiar with OBD2 in some form. The check engine light, or malfunction indicator light (MIL), on your dashboard is a direct output of the OBD2 system. When this light illuminates, it signals that your car has detected an issue. To diagnose this issue, a mechanic uses an OBD2 scanner.

This scanner connects to the OBD2 16-pin connector, typically located near the steering wheel. The scanner transmits ‘OBD2 requests’ to the car’s computer, and the car responds with ‘OBD2 responses’. These responses contain vital information such as speed, fuel level, and, importantly, Diagnostic Trouble Codes (DTCs). This streamlined communication drastically reduces diagnostic time and improves repair accuracy.

Understanding OBD2: The malfunction indicator light (MIL) signals issues diagnosed via the OBD2 system.

OBD2 and CAN Bus: A Powerful Partnership

While OBD2 is the diagnostic language, CAN bus (Controller Area Network) is often the communication network it uses, especially in modern vehicles. CAN bus is a robust and efficient communication standard that allows different parts of your car to talk to each other. Think of it as the nervous system of your vehicle, relaying messages between various electronic control units (ECUs).

Since 2008, CAN bus has become the mandatory lower-layer protocol for OBD2 in all cars sold in the US, as per ISO 15765 standards. This means that when you use an OBD2 scanner on a modern car, the communication is very likely happening over the CAN bus network.

This is where the CAN bus to OBD2 adapter becomes indispensable. It acts as a translator, allowing devices that speak the OBD2 protocol to communicate with vehicles using the CAN bus network. Without this adapter, direct communication would be impossible in most modern vehicles.

Does Your Car Use OBD2 and CAN Bus?

The answer is likely yes, especially if you own a non-electric car manufactured in the last two decades. OBD2 has been widely adopted globally, and CAN bus is the dominant communication protocol in modern automotive systems.

For older cars, even if a 16-pin OBD2 connector is present, it might not fully support the OBD2 protocol. Compliance depends on the vehicle’s manufacturing location and year. Here’s a general guideline:

OBD2 Compliance Guide: Check your vehicle’s origin and manufacturing date to determine OBD2 compliance.

A Brief History of OBD2 and CAN Bus Integration

OBD2’s origins trace back to California, where the California Air Resources Board (CARB) mandated OBD in all new cars from 1991 onwards for emission control.

The Society of Automotive Engineers (SAE) played a crucial role in standardizing OBD2, establishing standardized DTCs and the OBD connector (SAE J1962). This standardization ensured that diagnostic tools could be universally applied across different manufacturers.

The rollout of OBD2 was gradual but comprehensive:

1996: OBD2 became mandatory in the USA for cars and light trucks.
2001: Required in the EU for gasoline cars.
2003: Required in the EU for diesel cars (EOBD – European On-Board Diagnostics).
2005: OBD2 required in the US for medium-duty vehicles.
2008: US cars mandated to use ISO 15765-4 (CAN) as the foundation for OBD2 communication, solidifying the CAN bus to OBD2 adapter’s importance.
2010: OBD2 required in US heavy-duty vehicles.

OBD2 History for Emission Control: From emission standards to standardized diagnostics.

OBD2 Timeline: Key milestones in the standardization and adoption of OBD2.

OBD2 Future Trends: Remote diagnostics and the evolution towards OBD3.

The Future of OBD2: Adapting to Modern Vehicles

OBD2 is expected to remain relevant, though its form and function are evolving.

Originally designed for emission control, legislated OBD2 faces new challenges with the rise of electric vehicles (EVs). Interestingly, most modern EVs do not support standard OBD2 requests. Instead, they often use OEM-specific UDS (Unified Diagnostic Services) communication. This makes accessing data from EVs more complex, often requiring reverse engineering to decode proprietary protocols. However, for traditional combustion engine vehicles, OBD2 over CAN bus, and thus CAN bus to OBD2 adapters, will continue to be the standard for the foreseeable future.

Emerging standards like WWH-OBD (World Wide Harmonized OBD) and OBDonUDS are being developed to enhance OBD communication, leveraging UDS as a foundation. These advancements aim to address the limitations of current OBD2 implementations, especially in data richness and protocol flexibility.

The future of OBD2 also points towards increased connectivity. OBD3 concepts propose integrating telematics into all cars, enabling remote emission control checks and data monitoring. Devices like the CANedge2 WiFi CAN logger and CANedge3 3G/4G CAN logger already facilitate data transfer via WiFi/cellular networks.

However, the increasing use of OBD2 for third-party data access is facing pushback from car manufacturers. Concerns about data security and control are leading to proposals to limit OBD2 functionality during driving, potentially shifting data access control back to manufacturers. This could significantly impact the market for third-party OBD2 services and highlight the ongoing debate around automotive data ownership.

OBD2 in EVs: The shift away from standard OBD2 in electric vehicles and towards proprietary systems.

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OBD2 Standards: The Technical Foundation

OBD2 operates as a higher-layer protocol, functioning like a language built upon a communication method. CAN bus is that method, similar to a phone line for communication. This places OBD2 alongside other CAN-based higher-layer protocols such as J1939, CANopen, and NMEA 2000.

OBD2 standards define the OBD2 connector, lower-layer protocols, OBD2 parameter IDs (PIDs), and more. These standards are often represented using the 7-layer OSI model. Notably, both SAE (US standards) and ISO (EU standards) contribute to various layers, reflecting the global standardization effort. Many SAE and ISO standards are technically equivalent, such as SAE J1979 vs. ISO 15031-5 and SAE J1962 vs. ISO 15031-3.

OBD2 and CAN Bus in the OSI Model: Illustrating the layered standards for OBD2 communication over CAN.

OBD2 Connector Pinout: Diagram of a Type A OBD2 connector, highlighting pin functions.

The OBD2 Connector: SAE J1962 Standard

The 16-pin OBD2 connector, detailed in SAE J1962 / ISO 15031-3, provides easy access to your car’s data. The illustration above shows a Type A OBD2 pin connector, also known as the Data Link Connector (DLC). This is the physical interface where your CAN bus to OBD2 adapter plugs in.

Key features of the OBD2 connector include:

Location: Usually near the steering wheel, though sometimes hidden.
Pin 16: Provides battery power, often active even when the ignition is off.
Pinout: Varies depending on the communication protocol used.
CAN Bus: For CAN bus communication, pins 6 (CAN-H) and 14 (CAN-L) are typically used, which are the pins your CAN bus to OBD2 adapter will interface with.

OBD2 Connector Types: A vs. B

You might encounter both Type A and Type B OBD2 connectors. Type A is common in cars, while Type B is prevalent in medium and heavy-duty vehicles.

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

Type B connectors have an interrupted groove in the middle, distinguishing them from Type A. A Type B CAN bus to OBD2 adapter cable is generally compatible with both Type A and B sockets, while a Type A adapter may not fit into a Type B socket.

OBD2 Connector Types A and B: Comparison of connector types based on SAE J1962 standards.

OBD2 vs CAN Bus: Illustrating the relationship and standards governing OBD2 over CAN.

OBD2 and CAN Bus: ISO 15765-4 Details

ISO 15765-4, also known as Diagnostics over CAN (DoCAN), standardizes the CAN interface for OBD2 communication. It specifies requirements for the physical, data link, and network layers of the CAN bus when used for OBD2. This standard is crucial for ensuring interoperability between vehicles and diagnostic tools, and it directly impacts the design and functionality of CAN bus to OBD2 adapters.

Key specifications of ISO 15765-4 include:

CAN bus bit-rate: Must be either 250K or 500K.
CAN IDs: Can be 11-bit or 29-bit.
CAN IDs for OBD2: Specific CAN IDs are designated for OBD requests and responses.
Data Length: Diagnostic CAN frames must have a data length of 8 bytes.
Adapter Cable Length: The OBD2 adapter cable should not exceed 5 meters.

OBD2 CAN Identifiers: 11-bit and 29-bit

OBD2 communication over CAN bus relies on request/response message pairs. The CAN bus to OBD2 adapter is designed to handle these specific identifiers to facilitate communication.

In most cars, 11-bit CAN IDs are used for OBD2. Functional addressing, using CAN ID 0x7DF, broadcasts requests to all OBD2-compatible ECUs. Physical addressing, using CAN IDs 0x7E0-0x7E7, targets specific ECUs but is less commonly used.

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

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

OBD2 Request and Response Frames: Illustrating the structure of OBD2 communication frames.

OBD2 vs Proprietary CAN: Differentiating between standardized OBD2 data and OEM-specific CAN data.

OBD2 vs. Proprietary CAN Protocols

It’s important to understand that OBD2 is an additional protocol layer on top of the vehicle’s internal communication network. Vehicle ECUs primarily function using OEM-specific proprietary CAN protocols. These protocols are unique to each manufacturer and often to specific vehicle models and years. Without reverse engineering, this OEM-specific CAN data is generally inaccessible to third parties.

When you connect a CAN bus data logger to your car’s OBD2 connector, you might observe both OEM-specific CAN data and OBD2 data. However, many newer vehicles employ a ‘gateway’ that restricts access to OEM-specific CAN data through the OBD2 port, allowing only OBD2 communication. Therefore, the CAN bus to OBD2 adapter primarily facilitates access to the standardized OBD2 data, not the deeper OEM-specific network.

Think of OBD2 as a standardized diagnostic interface that runs alongside the manufacturer’s proprietary communication system. Your CAN bus to OBD2 adapter is specifically designed to tap into this standardized interface.

Bit-Rate and ID Validation for Reliable Connection

OBD2 over CAN bus can use two bit-rates (250K, 500K) and two CAN ID lengths (11-bit, 29-bit), resulting in four possible combinations. Modern cars commonly use 500K and 11-bit IDs. Robust external tools and CAN bus to OBD2 adapters should systematically validate these parameters to ensure reliable communication.

ISO 15765-4 outlines a systematic initialization sequence to determine the correct combination. This process leverages the fact that OBD2-compliant vehicles must respond to a mandatory OBD2 request. Incorrect bit-rate transmissions will result in CAN error frames, which can be detected to identify the correct bit-rate.

Newer versions of ISO 15765-4 address vehicles supporting OBD communication via OBDonUDS (OBD on Unified Diagnostic Services) instead of OBDonEDS (OBD on Emission Diagnostic Service). While this article primarily focuses on OBD2/OBDonEDS, it’s important to note the evolving landscape. Tools testing for OBDonEDS vs. OBDonUDS may send additional UDS requests to identify protocol support. In practice, OBDonEDS (also known as OBD2, SAE OBD, EOBD, or ISO OBD) is prevalent in most non-EV cars, while WWH-OBD is mainly used in EU trucks and buses.

OBD2 Bit-Rate and CAN ID Validation Flowchart: Steps to establish correct communication parameters according to ISO 15765-4.

Five Lower-Layer OBD2 Protocols: Overview of different protocols used for OBD2, with CAN (ISO 15765) being the most prevalent today.

Five Lower-Layer OBD2 Protocols: A Historical Perspective

While CAN bus (ISO 15765) is now the dominant lower-layer protocol for OBD2, particularly in vehicles manufactured post-2008, older cars may utilize other protocols. Understanding these historical protocols can be helpful when working with older vehicles. Note the pinouts of your OBD2 connector, as they can sometimes indicate the protocol in use.

The five lower-layer OBD2 protocols include:

ISO 15765 (CAN bus): Mandatory in US cars since 2008 and widely used today. This is the protocol your CAN bus to OBD2 adapter is designed for.
ISO14230-4 (KWP2000): Keyword Protocol 2000, common in 2003+ cars, especially in Asia.
ISO 9141-2: Used in EU, Chrysler, and Asian cars from 2000-2004.
SAE J1850 (VPW): Primarily used in older GM vehicles.
SAE J1850 (PWM): Primarily used in older Ford vehicles.

ISO-TP: Transporting OBD2 Messages Over CAN (ISO 15765-2)

All OBD2 data transmitted over CAN bus utilizes ISO-TP (ISO 15765-2), a transport protocol. This protocol allows for the transmission of data payloads exceeding the 8-byte limit of a standard CAN frame. ISO-TP is essential for OBD2 functions like retrieving the Vehicle Identification Number (VIN) or Diagnostic Trouble Codes (DTCs), which often require more than 8 bytes of data. ISO-TP provides mechanisms for segmentation, flow control, and reassembly of these larger messages. For a deeper dive, 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 message, the first data byte (PCI field) indicates the payload length (excluding padding), leaving 7 bytes for OBD2-related communication. Your CAN bus to OBD2 adapter and associated software will handle these ISO-TP details transparently.

ISO-TP Frame Types for OBD2: Illustrating Single Frame, First Frame, Consecutive Frame, and Flow Control frame types used in ISO-TP.

Decoding the OBD2 Diagnostic Message (SAE J1979, ISO 15031-5)

To effectively use a CAN bus to OBD2 adapter, understanding the structure of OBD2 messages is crucial. A simplified OBD2 CAN message consists of an identifier, a data length indicator (PCI field), and the data itself. The data field is further broken down into Mode, parameter ID (PID), and data bytes.

OBD2 Message Structure: Breakdown of an OBD2 message, showing Mode, PID, and data bytes within the CAN frame.

Example: OBD2 Request and Response in Action

Let’s examine a practical example: requesting ‘Vehicle Speed’.

An external tool, via a CAN bus to OBD2 adapter, sends a request message to the car with CAN ID 0x7DF and a 2-byte payload: Mode 0x01 and PID 0x0D. The car responds with a message on CAN ID 0x7E8 and a 3-byte payload. The vehicle speed value is encoded in the 4th byte of the CAN data field (byte 3 of the payload), in this case, 0x32 (decimal 50).

By consulting the OBD2 PID documentation for PID 0x0D, we can determine that the value 0x32 corresponds to a physical speed of 50 km/h. This simple example highlights the fundamental request-response mechanism and the role of PIDs in OBD2 communication.

OBD2 Request and Response Example: Request for Vehicle Speed (PID 0x0D) and the corresponding response.

OBD2 PID 0x0D – Vehicle Speed: Details on how PID 0x0D is used to retrieve vehicle speed data.

OBD2 Services (Modes): Overview of the 10 standardized OBD2 diagnostic services or modes.

The 10 OBD2 Services (Modes): Accessing Different Diagnostic Data

OBD2 defines 10 diagnostic services, also referred to as modes. Mode 0x01 is used to retrieve current real-time data, while other modes are designed for accessing and clearing diagnostic trouble codes (DTCs), retrieving freeze frame data, and more.

Not all vehicles are required to support all 10 OBD2 modes. Manufacturers may also implement OEM-specific OBD2 modes beyond the standardized set.

In OBD2 messages, the mode is indicated 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., a response to mode 0x01 will have mode 0x41). Your CAN bus to OBD2 adapter and software will manage these mode details.

OBD2 Parameter IDs (PIDs): Requesting Specific Data

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 such as speed, RPM, and fuel level. However, a vehicle might not support all PIDs within a given mode. In practice, most vehicles support only a subset of the standardized PIDs. Determining which PIDs are supported by your vehicle is a crucial step in effective OBD2 data retrieval.

One PID stands out as particularly important: mode 0x01 PID 0x00. If an emissions-related ECU supports any OBD2 services, it must support mode 0x01 PID 0x00. Responding to this PID, the vehicle ECU indicates its support for PIDs 0x01-0x20. This makes PID 0x00 a valuable tool for initial OBD2 compatibility testing. Similarly, PIDs 0x20, 0x40, 0x60, 0x80, 0xA0, and 0xC0 can be used to determine support for subsequent PID ranges within mode 0x01.

OBD2 Request and Response Frames (Repeated): Reinforcing the structure of OBD2 communication frames with PID context.

OBD2 PID Overview Tool: A helpful tool for exploring and understanding OBD2 Parameter IDs.

Tip: Utilizing an OBD2 PID Overview Tool

The appendices of SAE J1979 and ISO 15031-5 provide essential scaling information for standard OBD2 PIDs. This information allows you to convert the raw data received via your CAN bus to OBD2 adapter into meaningful physical values. Our CAN bus introduction explains the process of decoding CAN data in more detail.

For quick lookup of mode 0x01 PIDs, our OBD2 PID overview tool is invaluable. It assists in constructing OBD2 request frames and dynamically decodes OBD2 responses, streamlining your diagnostic workflow.

OBD2 PID overview tool
OBD2 PID Lookup Tool Link: Direct access to the online OBD2 PID tool.

Practical Guide: Logging and Decoding OBD2 Data

Let’s walk through a practical example of logging OBD2 data using a CANedge CAN bus data logger. The CANedge, when paired with a CAN bus to OBD2 adapter, becomes a powerful tool for vehicle data acquisition.

The CANedge allows you to define custom CAN frames for transmission, making it ideal for sending OBD2 requests. Connecting the CANedge to your vehicle is straightforward using our OBD2-DB9 adapter cable. This cable acts as a CAN bus to OBD2 adapter, physically interfacing the CANedge with your vehicle’s OBD2 port.

OBD2 Data Logger Setup: Illustrating the connection of a CAN bus data logger for OBD2 data acquisition.

Supported PIDs Test Results: Reviewing responses to ‘Supported PIDs’ requests using asammdf software.

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

As per ISO 15765-4, it’s essential to determine the correct bit-rate and CAN IDs for your specific vehicle. The CANedge, along with a CAN bus to OBD2 adapter, can be used for this validation process:

Bit-Rate Test: Send a CAN frame at 500K. If successful, proceed. If not, try 250K.
Subsequent Communication: Use the identified bit-rate for all further communication.
Supported PIDs Request: Send multiple ‘Supported PIDs’ requests (Mode 0x01 PID 0x00) and analyze the responses.
CAN ID Determination: Based on response IDs (e.g., 0x7E8, 0x7E9), determine if 11-bit or 29-bit IDs are in use.
Supported PID Identification: Analyze response data to identify supported PIDs for your vehicle.

We offer pre-configured settings for CANedge to simplify these initial tests. Most post-2008 non-EV cars typically support 40-80 PIDs using a 500K bit-rate, 11-bit CAN IDs, and the OBD2/OBDonEDS protocol.

The asammdf GUI screenshot illustrates typical responses to ‘Supported PIDs’ requests. Multiple responses to a single request (using ID 0x7DF) are common as it polls all ECUs. The ECM ECU (0x7E8) often supports all PIDs supported by other ECUs in this example, suggesting that using ‘Physical Addressing’ (ID 0x7E0) for subsequent requests can reduce bus load.

Step #2: Configuring OBD2 PID Requests for Data Logging

Once you’ve identified supported PIDs and communication parameters, configure your CANedge to request the PIDs of interest. This configuration, in conjunction with your CAN bus to OBD2 adapter, will enable targeted data logging.

Consider these points when configuring your OBD2 PID requests:

CAN IDs: Switch to ‘Physical Addressing’ request IDs (e.g., 0x7E0) to minimize multiple responses.
Request Spacing: Introduce a delay of 300-500 ms between OBD2 requests to prevent ECU overload and ensure reliable responses.
Battery Management: Implement triggers to stop requests when the vehicle is inactive to avoid battery drain.
Data Filtering: Set up filters to record only OBD2 responses, especially if OEM-specific CAN data is also present on the bus.

With these configurations, your CANedge, connected via a CAN bus to OBD2 adapter, is ready to log raw OBD2 data efficiently.

CANedge OBD2 Request List Example: A sample configuration of OBD2 PID requests for CANedge data logging.

Decoded OBD2 Data Visualization: asammdf software displaying DBC decoded and visualized OBD2 data.

Step #3: DBC Decoding of Raw OBD2 Data for Analysis

To analyze and visualize the logged raw OBD2 data, you need to decode it into physical values. This decoding process leverages the scaling information provided in ISO 15031-5/SAE J1979 and readily available online resources like Wikipedia.

We offer a free OBD2 DBC file that simplifies DBC decoding of raw OBD2 data in most CAN bus software tools. This DBC file, combined with your data logged via a CAN bus to OBD2 adapter, provides a complete solution for OBD2 data analysis.

Decoding OBD2 data is more complex than standard CAN signal decoding. Because different OBD2 PIDs are transmitted using the same CAN ID (e.g., 0x7E8), the CAN ID alone is insufficient to identify the signal. Instead, decoding requires considering the CAN ID, OBD2 mode, and OBD2 PID. This multiplexing technique, termed ‘extended multiplexing‘, is effectively handled by DBC files and tools that support it. Our OBD2 DBC file is specifically designed to address this complexity.

CANedge: Your OBD2 Data Logging Solution

The CANedge, used with a CAN bus to OBD2 adapter, provides an easy-to-use solution for recording OBD2 data directly to an 8-32 GB SD card. Simply connect it to your vehicle’s OBD2 port to start logging. Free software and APIs are available for data analysis, along with our dedicated OBD2 DBC file.

OBD2 logger intro CANedge
CANedge OBD2 Logger: Links to product information and OBD2 logger introduction.

OBD2 Multi-Frame Examples: ISO-TP in Practice

While many OBD2 interactions are single-frame, some operations, like retrieving VIN or DTCs, require multi-frame communication via ISO-TP. These examples illustrate ISO-TP in OBD2 and the role of a CAN bus to OBD2 adapter in facilitating these complex exchanges.

Multi-frame OBD2 communication involves 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 our CANedge configuration examples. Analyzing multi-frame OBD2 responses requires CAN software and API tools with ISO-TP support, such as the CANedge MF4 decoders.

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

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

The Vehicle Identification Number (VIN) is critical for telematics, diagnostics, and vehicle management. Retrieving the VIN using OBD2 requests (mode 0x09, PID 0x02) often involves multi-frame responses due to the VIN’s length. Your CAN bus to OBD2 adapter must support these multi-frame exchanges to successfully retrieve the VIN.

The tester tool initiates the process with a Single Frame request containing the PCI field (0x02), request service identifier (0x09), and PID (0x02).

The vehicle responds with a First Frame, indicating a total length of 20 bytes (0x014). This First Frame includes the mode (0x49), PID (0x02), and Number Of Data Items (NODI), which is 1 in this case. The subsequent 17 bytes contain the VIN itself, encoded in HEX, which can be converted to ASCII as described in our UDS introduction.

Example 2: OBD2 Multi-PID Request (6x) – Advanced Data Acquisition

OBD2 allows for requesting up to six mode 0x01 PIDs in a single request frame. The ECU will respond with data for the supported PIDs, potentially across multiple frames via ISO-TP. This advanced technique can increase data acquisition efficiency. However, it also complicates signal decoding, making generic OBD2 DBC files less effective. While a CAN bus to OBD2 adapter will handle the communication, decoding the data requires specialized tools or custom scripts.

We generally advise against using multi-PID requests for routine data logging due to the decoding complexities. However, for advanced users, it can be a powerful technique.

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

Decoding these responses via generic DBC files is challenging. It involves extended multiplexing with multiple instances within the payload. DBC files would need to account for the specific payload position of each PID, making generalization across different vehicles difficult. For complex multi-PID requests, custom scripts that interpret responses in conjunction with request messages may be necessary.

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

OBD2 mode 0x03, ‘Show stored Diagnostic Trouble Codes’, is used to retrieve emissions-related DTCs. The request frame for this mode does not include a PID. The ECU responds with the number of stored DTCs, followed by the DTC codes themselves, each DTC occupying 2 data bytes. Multi-frame responses are common when more than two DTCs are stored. Your CAN bus to OBD2 adapter facilitates this DTC retrieval process.

The 2-byte DTC value is structured according to ISO 15031-5/ISO 15031-6. The first two bits define 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 like repairpal.com.

The example below shows a response from an ECU with six stored DTCs.

OBD2 DTC Decoding Example: Breakdown of DTC data bytes and their interpretation according to OBD2 standards.

Real-World Applications of OBD2 Data Logging

OBD2 data, accessed via a CAN bus to OBD2 adapter and logged with tools like CANedge, has numerous practical applications in vehicle diagnostics, maintenance, and data analysis.

Car Data Logging for Performance and Efficiency

OBD2 data logging in cars can be used to optimize fuel consumption, improve driving habits, validate prototype parts, and even for insurance telematics. By tracking parameters like speed, RPM, throttle position, and fuel consumption, drivers and fleet managers can gain valuable insights into vehicle performance and efficiency.

obd2 logger
OBD2 Logger Link: Access to OBD2 data logger product information.

Real-Time Car Diagnostics and Troubleshooting

OBD2 interfaces, when used with software like SavvyCAN, enable real-time streaming of human-readable OBD2 data. This is invaluable for diagnosing vehicle issues as they occur, providing mechanics and technicians with live data for pinpointing problems and verifying repairs.

obd2 streaming
OBD2 Streaming Interface Link: Access to OBD2 streaming interface product information.

Predictive Maintenance and Fleet Management

Cloud-connected IoT OBD2 loggers facilitate predictive maintenance for cars and light trucks. By continuously monitoring OBD2 data and transmitting it to the cloud, potential breakdowns can be predicted and avoided. This is particularly beneficial for fleet management, minimizing downtime and maintenance costs.

predictive maintenance
Predictive Maintenance Solutions Link: Access to predictive maintenance and IoT solutions.

Vehicle Black Box Recording for Accountability and Analysis

An OBD2 logger can function as a ‘black box’ for vehicles or equipment. Recording OBD2 data provides objective evidence in case of disputes, accidents, or warranty claims. This black box functionality is valuable for insurance companies, fleet operators, and vehicle manufacturers.

can bus blackbox
Black Box CAN Logger Link: Access to black box CAN logger product information.

Do you have an OBD2 data logging application in mind? Contact us for expert guidance and support!

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

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