When Was OBD2 Mandatory? Understanding the OBD-II Mandate and Its Impact on Vehicle Diagnostics

Need a simple, practical intro to OBD2?

In this guide, we delve into the On-Board Diagnostics (OBD2) protocol, focusing on when OBD2 became mandatory and its significance for vehicle owners and technicians. We’ll cover the OBD2 connector, OBD2 Parameter IDs (PIDs), and its connection to the CAN bus system.

Note: This is a practical intro designed to help you understand the OBD2 mandate and its implications. You’ll also learn about requesting and decoding OBD2 data, key use cases for data logging, and valuable practical tips.

Discover why this guide is considered a top resource for understanding OBD2, particularly regarding the crucial question: “When Was Obd2 Mandatory?”

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

Decoding OBD2: Your Vehicle’s Diagnostic Window

OBD2, or On-Board Diagnostics version 2, is essentially your car’s internal health monitoring system. It’s a standardized protocol that allows access to crucial diagnostic trouble codes (DTCs) and real-time vehicle data through the OBD2 connector. This standardization is key to understanding when OBD2 became mandatory, as it was government regulations that drove this unified approach.

You’ve likely encountered OBD2 in action without even realizing it. Think about the malfunction indicator light, commonly known as the “check engine light,” on your dashboard.

This light is your vehicle’s way of signaling that something is amiss. When you take your car to a mechanic, they use an OBD2 scanner to pinpoint the problem.

This process involves connecting the OBD2 reader to the OBD2 16-pin connector, typically located beneath the steering wheel. The scanner transmits ‘OBD2 requests’ to the car’s computer system, and the car responds with ‘OBD2 responses’. These responses can include vital information such as speed, fuel level, and Diagnostic Trouble Codes (DTCs), significantly speeding up the troubleshooting and repair process. The standardization of this system is directly linked to when OBD2 was mandated, ensuring consistent diagnostic procedures across different vehicle makes and models.

Understanding OBD2: On-Board Diagnostics system featuring the Malfunction Indicator Light (MIL) and a scan tool interface.

OBD2 Compatibility: Is Your Car Equipped?

The question “when was OBD2 mandatory?” is closely tied to vehicle compatibility. For most modern vehicles, the answer is a resounding Probably, yes!

Nearly all newer gasoline and diesel cars, with the exception of electric vehicles in some regions, are equipped with OBD2 and often operate on the Controller Area Network (CAN) bus. However, for older vehicles, the presence of a 16-pin OBD2 connector doesn’t automatically guarantee OBD2 compliance. As scantool.net explains, older connectors might not fully support the OBD2 protocol. A key indicator of compliance is the vehicle’s manufacturing date and the market for which it was originally intended:

OBD2 Compliance Guide: Visual representation of OBD2 adoption timelines in the EU and US markets, highlighting the years when compliance became standard.

The History of OBD2: Driven by Emissions Standards

To fully answer “when was OBD2 mandatory?”, we need to delve into its historical roots. OBD2’s story begins in California, driven by the stringent emission control regulations of the California Air Resources Board (CARB). Recognizing the need for standardized vehicle diagnostics for emission monitoring, CARB mandated OBD in all new cars sold in California starting from 1991. This initial mandate was a precursor to the nationwide adoption we see today.

Building upon this Californian initiative, the Society of Automotive Engineers (SAE) played a crucial role in standardizing the diagnostic landscape. SAE recommended the OBD2 standard, which included standardized Diagnostic Trouble Codes (DTCs) and a universal OBD connector. This standardization was formalized through SAE J1962, laying the groundwork for consistent diagnostics across all vehicle manufacturers. This was a critical step towards making OBD2 mandatory on a larger scale.

From these foundations, the OBD2 standard was progressively implemented across the United States and Europe:

1996: OBD2 Mandate in the USA for Cars and Light Trucks: This marked the first major step in nationwide OBD2 adoption. 1996 is the year OBD2 became mandatory for all new cars and light trucks sold in the United States. This mandate was a direct result of federal legislation aimed at improving air quality and reducing vehicle emissions.
2001: OBD2 Requirement in the EU for Gasoline Cars: The European Union followed suit, mandating OBD2 (specifically EOBD, European On-Board Diagnostics) for all new gasoline passenger cars sold within the EU starting in 2001. This was a significant expansion of the OBD2 mandate beyond North America.
2003: OBD2 Requirement in the EU for Diesel Cars (EOBD): Extending the European mandate further, OBD2 (EOBD) became mandatory for all new diesel passenger cars sold in the EU from 2003 onwards. This ensured comprehensive emissions monitoring for both gasoline and diesel vehicles in Europe.
2005: OBD2 Mandate in the US for Medium-Duty Vehicles: The US mandate broadened to include medium-duty vehicles, ensuring that a wider range of commercial vehicles also adhered to OBD2 standards for emissions control.
2008: US Cars to Use ISO 15765-4 (CAN) as OBD2 Basis: A technological shift occurred with the mandate that all US vehicles must use ISO 15765-4 (CAN – Controller Area Network) as the communication protocol for OBD2. This standardized the communication layer, enhancing reliability and data exchange speed.
2010: OBD2 Mandate in US Heavy-Duty Vehicles: Finally, the OBD2 mandate in the US reached its full scope, encompassing heavy-duty vehicles. By 2010, OBD2 was mandatory for virtually all new vehicles sold in the United States, from passenger cars to heavy-duty trucks.

This step-by-step rollout clearly answers the question “when was OBD2 mandatory?” by showing the progressive expansion of the mandate across vehicle types and geographical regions, driven primarily by the need for effective emissions control.

OBD2 History Timeline: Graphical representation of the key milestones in OBD2 history, highlighting the evolution of emission control standards and OBD2 adoption.

OBD2 History Timeline Overview: A detailed timeline providing a visual summary of the historical progression of On-Board Diagnostics, emphasizing key dates and regulatory changes.

Future of OBD: Conceptual image representing OBD3 and the trend towards remote diagnostics, emissions testing, cloud connectivity, and IoT integration.

The Future of OBD2: Evolution and Adaptation

While we’ve established when OBD2 became mandatory, the story of OBD2 is far from over. It continues to evolve, adapting to the changing automotive landscape.

Initially designed for emissions control and testing, legislated OBD2 faces new challenges and opportunities, particularly with the rise of electric vehicles. Interestingly, electric vehicles are not currently required to support OBD2 in the same way as internal combustion engine vehicles. This is reflected in the fact that most modern EVs do not support standard OBD2 requests. Instead, they often utilize OEM-specific UDS (Unified Diagnostic Services) communication protocols. This OEM-specific approach makes it challenging to access and decode data from EVs, except in cases where reverse engineering efforts have successfully decoded the proprietary protocols. However, initiatives are underway to standardize diagnostics for EVs as well, which may impact the future of OBD2 mandates.

Despite these challenges, OBD2 remains relevant and is implemented in diverse ways. However, its limitations in data richness and lower-layer protocols have spurred the development of modern alternatives like WWH-OBD (World-Wide Harmonized OBD) and OBDonUDS (OBD on UDS). Both of these advancements aim to enhance and streamline OBD communication by utilizing the UDS protocol as a foundation. For a deeper understanding of these protocols, our intro to UDS provides valuable insights.

In our increasingly connected world, traditional OBD2 testing methods can seem outdated. Manually performing emission control checks is both time-consuming and costly.

The proposed solution for the future is OBD3: Integrating Telematics into Vehicles.

OBD3 envisions equipping all vehicles with a small radio transponder, similar to those used for electronic toll collection. This technology would enable vehicles to transmit their vehicle identification number (VIN) and DTCs wirelessly via WiFi to a central server for automated checks.

Many devices already facilitate the wireless transmission of CAN or OBD2 data, such as the CANedge2 WiFi CAN logger and the CANedge3 3G/4G CAN logger.

While this offers convenience and cost savings, it also raises political and privacy concerns related to surveillance. The implementation of OBD3 and its associated telematics features will likely be influenced by ongoing debates about data privacy and vehicle data access.

The original purpose of OBD2 was for stationary emission controls. However, today, OBD2 is extensively used by third parties to generate real-time vehicle data through OBD2 dongles, CAN loggers and other devices. This expanded use is now being reconsidered by some automotive manufacturers. The German car industry, for example, is exploring ways to limit third-party access to OBD2 data, as reported by eenewsautomotive.com:

OBD has been designed to service cars in repair shops. In no way has it been intended to allow third parties to build a form of data-driven economy on the access through this interface.

– Christoph Grote, SVP Electronics, BMW (2017)

The proposal suggests deactivating OBD2 functionality while driving and instead collecting vehicle data on a central server controlled by the manufacturer. This would give manufacturers control over the burgeoning field of ‘automotive big data’.

Arguments for this change often cite security concerns, such as reducing the risk of car hacking. However, many industry observers view this as a commercially motivated move to control vehicle data, as Navixy.com discusses. Whether this trend gains traction remains to be seen, but it could significantly disrupt the market for OBD2-based third-party services. The ongoing evolution of OBD2, driven by technological advancements and data privacy considerations, means the answer to “when was OBD2 mandatory?” is not just a historical point, but a starting point for understanding the future of vehicle diagnostics.

OBD2 Future in EVs: Illustration depicting the potential future where electric vehicles may restrict access to data via the OBD2 connector, highlighting challenges in data accessibility.

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OBD2 Standards: Defining the Diagnostic Framework

Understanding when OBD2 became mandatory also requires knowledge of the standards that underpin it. On-Board Diagnostics, OBD2, operates as a higher-layer protocol – like a language – while CAN functions as the communication method – analogous to a phone line. This makes OBD2 comparable to other CAN-based higher-layer protocols such as J1939, CANopen, and NMEA 2000.

Specifically, OBD2 standards define the OBD2 connector, lower-layer protocols, OBD2 Parameter IDs (PIDs), and more. These standards are organized within a 7-layer OSI model, and the following sections will focus on the most critical aspects.

In the OSI model context, you’ll notice that both SAE and ISO standards cover multiple layers. This reflects the standards developed for OBD in the USA (SAE) and Europe (ISO). Many of these standards are technically very similar, for instance, SAE J1979 and ISO 15031-5, and SAE J1962 and ISO 15031-3. These overlapping standards highlight the global effort to standardize vehicle diagnostics following the initial OBD2 mandates.

OBD2 vs CAN Bus OSI Model: Diagram illustrating the 7-layer OSI model, contrasting OBD2 and CAN Bus standards, and referencing ISO 15765 and ISO 11898.

OBD2 Connector Pinout: Diagram showing the pin configuration for a Type A female OBD2 connector, also known as a Data Link Connector (DLC).

The OBD2 Connector: SAE J1962 Standard

The 16-pin OBD2 connector is your physical interface for accessing vehicle data. It’s standardized under SAE J1962 / ISO 15031-3, ensuring uniformity across vehicles, which is a direct benefit of when OBD2 became mandatory.

The illustration shows a Type A OBD2 pin connector, also known as a Data Link Connector (DLC). Key points to note:

The connector is usually near the steering wheel, but its exact location can be discreetly hidden in some vehicles.
Pin 16 provides battery power, often even when the ignition is off, allowing for diagnostics without the engine running.
The OBD2 pinout configuration varies depending on the communication protocol used by the vehicle.
CAN bus, the most prevalent lower-layer protocol, typically uses pins 6 (CAN-High) and 14 (CAN-Low) for data transmission.

OBD2 Connector Types: A vs. B

In practical applications, you might encounter both Type A and Type B OBD2 connectors. Type A is typically found in passenger cars, while Type B is more common in medium and heavy-duty vehicles. Understanding these differences is important, especially when considering OBD2 compliance across different vehicle categories.

As shown in the illustration, both types have similar OBD2 pinouts but differ in power supply outputs: 12V for Type A and 24V for Type B. Baud rates can also vary; cars typically use 500K, while heavy-duty vehicles often use 250K (with increasing support for 500K in newer models).

A key physical distinction is that the Type B OBD2 connector has an interrupted groove in the middle, unlike Type A. This means a Type B OBD2 adapter cable is compatible with both Type A and B sockets, while a Type A adapter will not fit into a Type B socket. This physical incompatibility underscores the importance of using the correct adapter for the vehicle type, especially in commercial settings where Type B connectors are common due to the OBD2 mandates for medium and heavy-duty vehicles.

OBD2 Connector Type A vs B: Comparison diagram of OBD2 Connector Type A and Type B as per SAE J1962, highlighting differences in 12V and 24V power supply for cars, vans, and trucks.

OBD2 vs CAN bus ISO15765: Diagram illustrating the relationship between OBD2 and CAN bus, emphasizing the ISO 15765 standards for communication protocols.

OBD2 and CAN Bus: ISO 15765-4 Protocol

Since 2008, CAN bus has been the mandated lower-layer protocol for OBD2 in all vehicles sold in the US, as per ISO 15765. This standardization is a direct outcome of the OBD2 mandate and the need for reliable, high-speed communication for vehicle diagnostics.

ISO 15765-4 (also known as Diagnostics over CAN or DoCAN) specifies a set of constraints applied to the CAN standard (ISO 11898). It standardizes the CAN interface for diagnostic equipment, focusing on the physical, data link, and network layers:

CAN bus bit-rate must be either 250K or 500K, providing flexibility while ensuring compatibility.
CAN IDs can be 11-bit or 29-bit, accommodating both standard and extended CAN identifiers.
Specific CAN IDs are designated for OBD requests and responses, ensuring clear communication channels for diagnostic data.
Diagnostic CAN frame data length is fixed at 8 bytes, optimizing data transmission efficiency.
OBD2 adapter cable length is limited to 5 meters, minimizing signal degradation and ensuring reliable communication.

OBD2 CAN Identifiers: 11-bit and 29-bit

OBD2 communication relies on request/response message exchanges. Understanding these identifiers is key to interpreting OBD2 data and appreciating the standardization efforts that followed when OBD2 became mandatory.

In most passenger cars, 11-bit CAN IDs are used for OBD2 communication. The ‘Functional Addressing’ ID is 0x7DF, which is used to query all OBD2-compatible ECUs (Electronic Control Units) to check if they have data related to the requested parameter, as defined in ISO 15765-4. ‘Physical Addressing’ requests, using CAN IDs ranging from 0x7E0 to 0x7E7, can be directed to specific ECUs but are less commonly used in general OBD2 diagnostics.

ECUs respond using 11-bit IDs in the range of 0x7E8 to 0x7EF. The most common response ID is 0x7E8, typically originating from the ECM (Engine Control Module), with 0x7E9 (TCM, Transmission Control Module) being another frequent response ID.

In some vehicle types, particularly vans and light, medium, and heavy-duty vehicles, OBD2 communication may utilize extended 29-bit CAN identifiers instead of 11-bit IDs. This is more prevalent in commercial vehicles, aligning with the broader scope of OBD2 mandates across different vehicle classes.

For 29-bit CAN identifiers, the ‘Functional Addressing’ CAN ID is 0x18DB33F1.

Responses in this format use CAN IDs ranging from 0x18DAF100 to 0x18DAF1FF, with common response IDs being 0x18DAF110 and 0x18DAF11E. These response IDs are also sometimes represented in the ‘J1939 PGN’ format, specifically PGN 0xDA00 (55808), which is designated as ‘Reserved for ISO 15765-2’ in the J1939-71 standard. This cross-referencing highlights the interconnectedness of different automotive communication standards in the context of OBD2 mandates.

OBD2 Request/Response Frames: Diagram illustrating the structure of OBD2 protocol request and response frames, showing PID data parameters.

OBD2 vs Proprietary CAN bus: Conceptual image contrasting OBD2 and OEM-specific CAN bus data, illustrating the differences in accessibility and standardization.

OBD2 vs. Proprietary CAN Protocols: Understanding the Difference

It’s crucial to understand that your vehicle’s ECUs operate using proprietary CAN protocols defined by the original equipment manufacturer (OEM), independently of OBD2. These OEM-specific CAN protocols are tailored to the particular vehicle brand, model, and year. Unless you are the OEM, interpreting this proprietary CAN data is generally not possible without reverse engineering efforts. OBD2, in contrast, is a standardized layer built on top of these proprietary systems, largely driven by when OBD2 became mandatory for emissions compliance.

When you connect a CAN bus data logger to your car’s OBD2 connector, you might observe OEM-specific CAN data, typically broadcast at high rates (1000-2000 frames/second). However, many newer vehicles incorporate a ‘gateway’ that restricts access to this raw CAN data through the OBD2 port, allowing only standardized OBD2 communication.

In essence, think of OBD2 as an ‘additional’ higher-layer protocol that runs parallel to the OEM-specific protocol. OBD2 provides a standardized diagnostic interface, primarily for emissions-related data and basic vehicle parameters, while the OEM protocol manages the vehicle’s core functions and may include a much wider range of data points, although these are typically proprietary and not accessible through the standard OBD2 port. The separation between these protocols is important to consider when thinking about the implications of when OBD2 was mandated and what it practically means for vehicle data access.

Bit-Rate and ID Validation for OBD2 Communication

As mentioned, OBD2 may use either 250K or 500K bit rates and 11-bit or 29-bit CAN IDs, leading to four possible protocol combinations. Modern cars commonly use 500K and 11-bit IDs, but diagnostic tools should systematically verify these parameters to ensure correct communication. This validation process is essential for reliable diagnostics and is part of the standardized procedures that developed alongside the OBD2 mandates.

ISO 15765-4 provides guidelines for a systematic initialization sequence to determine the correct combination, as illustrated in the flowchart. The method leverages the requirement that OBD2-compliant vehicles must respond to a specific mandatory OBD2 request (see the OBD2 PID section for details). It also accounts for the fact that transmitting data at an incorrect bit rate will result in CAN error frames, which can be detected by diagnostic tools.

Newer versions of ISO 15765-4 acknowledge that vehicles may support OBD communication via OBDonUDS (OBD on Unified Diagnostic Services) rather than OBDonEDS (OBD on Emission Diagnostic Service). This article primarily focuses on OBD2/OBDonEDS (as per ISO 15031-5/SAE J1979) as it is the most widely used standard in non-EV vehicles today. WWH-OBD/OBDonUDS (as per ISO 14229, ISO 27145-3/SAE J1979-2) is more commonly found in EU trucks and buses.

To test for OBDonEDS vs. OBDonUDS protocol support, advanced diagnostic tools may send additional request messages, specifically UDS requests with 11-bit/29-bit functional address IDs for service 0x22 and data identifier (DID) 0xF810 (protocol identification). Vehicles supporting OBDonUDS should have ECUs that respond to this DID.

In practice, OBDonEDS (also referred to as OBD2, SAE OBD, EOBD, or ISO OBD) is the predominant protocol in most non-electric vehicles today, while WWH-OBD is primarily used in European trucks and buses. The distinction between these protocols and the validation processes are crucial for ensuring effective diagnostics, particularly in diverse vehicle fleets that must comply with OBD2 mandates.

OBD2 bit-rate and CAN ID validation: Flowchart illustrating the process of OBD2 bit-rate and CAN ID validation according to ISO 15765-4 standards.

OBD2 Standards KWP2000 SAE J1850 ISO9141 ISO 15765: Diagram outlining the five lower-layer OBD2 protocols, including CAN, KWP2000, SAE J1850, and ISO 9141, highlighting ISO 15765.

Five Lower-Layer OBD2 Protocols: A Historical Perspective

While CAN is now the dominant lower-layer protocol for OBD2 as per ISO 15765, especially in vehicles manufactured after OBD2 became mandatory in 2008 in the US, older vehicles (pre-2008) may use one of four other lower-layer protocols. Understanding these legacy protocols is helpful when working with older vehicles. The OBD2 connector pinouts can sometimes indicate which protocol is in use.

ISO 15765 (CAN bus): Mandatory in US cars since 2008 and now the most common protocol globally. Its adoption is a direct consequence of the evolving OBD2 mandates.
ISO14230-4 (KWP2000): Keyword Protocol 2000 was frequently used in 2003+ vehicles, particularly in Asia and Europe, before the widespread adoption of CAN.
ISO 9141-2: Used in European, Chrysler, and Asian cars manufactured between 2000 and 2004, representing an earlier phase of OBD2 implementation.
SAE J1850 (VPW – Variable Pulse Width Modulation): Primarily used in older General Motors (GM) vehicles in North America.
SAE J1850 (PWM – Pulse Width Modulation): Predominantly used in older Ford vehicles in North America.

ISO-TP: Transporting OBD2 Messages via ISO 15765-2

All OBD2 data communication over CAN bus relies on a transport protocol called ISO-TP (ISO 15765-2). This protocol is essential because it enables the transmission of data payloads larger than the 8-byte limit of a standard CAN frame. ISO-TP is crucial for OBD2 functions that require larger data packets, such as retrieving the Vehicle Identification Number (VIN) or Diagnostic Trouble Codes (DTCs). ISO 15765-2 handles segmentation, flow control, and reassembly of these larger messages, ensuring reliable data transfer for comprehensive diagnostics, which became increasingly important as OBD2 mandates expanded to cover more complex vehicle systems. For a detailed explanation of ISO-TP, refer to our intro to UDS.

However, much of the real-time data exchanged in OBD2 fits within a single CAN frame. In these cases, ISO 15765-2 specifies the use of a ‘Single Frame’ (SF) format. In a Single Frame, the first data byte (known as the PCI field or Protocol Control Information) indicates the payload length (excluding padding). This leaves 7 bytes within the CAN frame for the actual OBD2-related communication. This efficient use of single frames for smaller data packets optimizes communication overhead, especially for frequently requested parameters, contributing to the overall effectiveness of OBD2 diagnostics, which has been a key objective since OBD2 became mandatory.

ISO 15765-2 ISO-TP OBD2 frame types: Diagram illustrating different frame types in ISO 15765-2 ISO-TP protocol used for OBD2 communication, including Single Frame, First Frame, Consecutive Frame, and Flow Control Frame.

The OBD2 Diagnostic Message: SAE J1979, ISO 15031-5 Standards

To gain a deeper understanding of OBD2 communication over CAN, let’s examine the structure of a raw ‘Single Frame’ OBD2 CAN message. In simplified terms, an OBD2 message comprises a CAN identifier, a data length indicator (PCI field), and the actual data payload. The data payload is further structured into a Mode byte, a Parameter ID (PID) byte, and subsequent data bytes. Understanding this structure is essential for anyone working with OBD2 data and appreciating the standardization that followed when OBD2 became mandatory.

OBD2 PIDs OBD-ii Message Structure Breakdown Explained: Diagram breaking down the structure of an OBD2 message frame, explaining the roles of Mode, PID, and Data Bytes.

OBD2 Request/Response Example: Retrieving Vehicle Speed

Before diving into the specifics of OBD2 message components, let’s consider a practical example: requesting and receiving vehicle speed data. This example illustrates the request-response mechanism fundamental to OBD2 communication and how standardized PIDs (Parameter IDs) are used to access specific vehicle parameters, a system put in place following the OBD2 mandate.

In this scenario, an external diagnostic tool initiates a request by sending a CAN message to the vehicle. This request message uses CAN ID 0x7DF and includes a 2-byte payload: Mode 0x01 and PID 0x0D. Mode 0x01 signifies “Show current data,” and PID 0x0D is the Parameter ID for “Vehicle Speed.”

The vehicle’s ECU responds to this request with a CAN message using CAN ID 0x7E8 and a 3-byte payload. This response includes the vehicle speed value in the 4th byte of the CAN data frame, represented as 0x32 in hexadecimal. Converting 0x32 from hexadecimal to decimal gives 50.

By consulting the OBD2 PID documentation for PID 0x0D, we can determine the decoding rules for vehicle speed. In this case, the value 50 directly corresponds to a physical speed of 50 km/h. This example demonstrates the simplicity and effectiveness of OBD2 in accessing real-time vehicle data, a capability that has become increasingly important since OBD2 became mandatory for emissions monitoring and diagnostics.

OBD2 request 7DF response 7e8: Example illustrating an OBD2 request with CAN ID 7DF and a response with CAN ID 7E8, demonstrating a typical OBD2 communication sequence.

OBD2 PID example Vehicle Speed 0D: Example focusing on OBD2 PID 0D for Vehicle Speed, showing how to interpret and decode the PID value.

OBD2 services modes current data freeze frame clear dtc: Overview of the 10 OBD2 service modes, including modes for current data, freeze frame, and clearing DTCs, highlighting the range of diagnostic services available.

The 10 OBD2 Services (Modes): Accessing Diagnostic Functions

OBD2 defines 10 diagnostic services, also referred to as modes, that provide access to various diagnostic functions. Mode 0x01, as seen in the vehicle speed example, is used to retrieve current real-time data parameters. Other modes are used to access and manage Diagnostic Trouble Codes (DTCs), retrieve freeze frame data (snapshots of data when a DTC was set), and perform other diagnostic functions. These standardized modes are a cornerstone of OBD2, ensuring consistent diagnostic procedures across vehicle manufacturers, a key aspect of when OBD2 became mandatory.

It’s important to note that vehicles are not required to support all 10 OBD2 modes. Furthermore, manufacturers may implement OEM-specific modes beyond the 10 standardized modes to provide access to proprietary diagnostic information. However, the standardized modes are essential for basic emissions-related diagnostics and are widely supported due to regulatory requirements that stemmed from the OBD2 mandates.

In OBD2 messages, the service mode is indicated in the second byte of the data payload. In a request message, the mode is included directly (e.g., 0x01 for Mode 1). In a response message, 0x40 is added to the requested mode (e.g., a response to Mode 0x01 will have a mode byte of 0x41). This convention helps to distinguish between request and response messages and is part of the standardized OBD2 protocol specifications.

OBD2 Parameter IDs (PIDs): Requesting Specific Data

Within each OBD2 service mode, Parameter IDs (PIDs) are used to specify the particular data parameter being requested or reported. PIDs are numeric codes that correspond to specific vehicle parameters, such as engine speed, coolant temperature, intake manifold pressure, and many others. The standardization of PIDs is a crucial aspect of OBD2, allowing diagnostic tools to request and interpret data from different vehicles in a consistent manner, a benefit directly resulting from when OBD2 became mandatory.

For example, within Mode 0x01 (Show current data), there are approximately 200 standardized PIDs defined. These PIDs cover a wide range of real-time data parameters related to engine performance, emissions, and vehicle operation. Common PIDs include those for vehicle speed, engine RPM, coolant temperature, throttle position, fuel level, and oxygen sensor readings. However, it’s important to note that a specific vehicle may not support all standardized OBD2 PIDs within a given mode. In practice, most vehicles support only a subset of the available PIDs. The specific PIDs supported can vary depending on the vehicle make, model, and year of manufacture.

In this context, 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. When a diagnostic tool sends a request for Mode 0x01 PID 0x00, the vehicle’s ECU responds by providing a bitmask indicating which PIDs in the range of 0x01 to 0x20 are supported by that ECU. This makes PID 0x00 a fundamental tool for OBD2 compatibility testing and for discovering the range of supported PIDs. Furthermore, PIDs 0x20, 0x40, 0x60, 0x80, 0xA0, and 0xC0 in Mode 0x01 serve a similar purpose, each indicating the support status for subsequent blocks of 32 PIDs (0x21-0x40, 0x41-0x60, and so on, up to 0xE1-0x100). These “Supported PIDs” PIDs are essential for diagnostic tools to dynamically determine the capabilities of a vehicle’s OBD2 implementation, ensuring efficient and accurate data requests, a capability mandated alongside OBD2 regulations.

OBD2 Request/Response Frames with PID Parameters: Diagram illustrating OBD2 protocol request and response frames, emphasizing the role of PID (Parameter ID) in data requests.

OBD2 PID Overview Tool: Screenshot of an OBD2 PID overview tool interface, showing Service 01 and options for PID selection and data interpretation.

Tip: Utilizing an OBD2 PID Overview Tool for Efficient Diagnostics

The appendices of SAE J1979 and ISO 15031-5 standards documents provide detailed scaling and decoding information for standard OBD2 PIDs. This information is essential for converting raw OBD2 data bytes into meaningful physical values, as explained in our CAN bus introduction. These standards documents are the definitive resource for understanding OBD2 mandates and technical specifications.

For quick and convenient access to OBD2 PID information, especially Mode 0x01 PIDs, consider using our OBD2 PID overview tool. This tool simplifies the process of constructing OBD2 request frames and dynamically decoding OBD2 responses. It provides a user-friendly interface to look up PID definitions, scaling factors, and units, making it easier to interpret OBD2 data and troubleshoot vehicle issues.

OBD2 PID overview tool

Logging and Decoding OBD2 Data: A Practical Guide

In this section, we’ll walk through a practical example of how to log OBD2 data using the CANedge CAN bus data logger. The CANedge is a versatile tool that allows you to configure custom CAN frames for transmission, making it well-suited for OBD2 data logging applications. Understanding how to log and decode OBD2 data is essential for leveraging the diagnostic capabilities enabled by when OBD2 became mandatory.

Once configured, the CANedge device can be easily connected to your vehicle’s OBD2 port using our OBD2-DB9 adapter cable. This setup allows you to capture OBD2 data directly from your vehicle for analysis and diagnostics.

OBD2 PID data logger request 7df 7e8: Diagram illustrating an OBD2 data logger sending a request with CAN ID 7DF and receiving a response with CAN ID 7E8, showing a typical data logging setup.

OBD2 Supported PIDs Test: Screenshot from asammdf software displaying OBD2 validation PID test responses, used to determine supported PIDs.

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

As discussed earlier, ISO 15765-4 outlines the procedure to determine the correct bit-rate and CAN IDs for OBD2 communication in a specific vehicle. You can use the CANedge data logger to perform these tests, as detailed below (refer to the CANedge Intro for comprehensive instructions):

Bit-Rate Test: Start by attempting to transmit a CAN frame at 500K bit-rate. Monitor for successful transmission. If unsuccessful, repeat the test at 250K. Successful transmission indicates the correct bit-rate for OBD2 communication in the target vehicle.
Bit-Rate Confirmation: Use the identified bit-rate for all subsequent OBD2 communication with the vehicle.
Supported PID Discovery: Send multiple ‘Supported PIDs’ requests (Mode 0x01 PIDs 0x00, 0x20, 0x40, etc.) to the vehicle and carefully review the responses.
CAN ID Determination: Based on the response CAN IDs, determine whether the vehicle is using 11-bit or 29-bit CAN identifiers for OBD2 communication. Typically, responses using IDs in the 0x7E8-0x7EF range indicate 11-bit IDs, while responses in the 0x18DAF100-0x18DAF1FF range suggest 29-bit IDs.
Supported PID Identification: Analyze the response data from the ‘Supported PIDs’ requests to identify the specific OBD2 PIDs supported by the vehicle’s ECUs. The response data is typically a bitmask indicating PID support.

We provide pre-configured CANedge configurations to simplify these initial tests. These configurations automate the process of sending test frames and help you quickly determine the communication parameters for your vehicle.

Most non-electric vehicles manufactured in 2008 or later typically support between 40 and 80 OBD2 PIDs using a 500K bit-rate, 11-bit CAN IDs, and the OBD2/OBDonEDS protocol. However, it’s essential to perform these validation steps to confirm the specific communication parameters for your vehicle.

As illustrated in the asammdf GUI screenshot, it’s common to receive multiple responses to a single OBD request, especially when using the functional addressing request ID 0x7DF. This is because the 0x7DF request ID polls all OBD2-compliant ECUs for a response. Since all OB