Decoding the 2008 BMW OBD2 Protocol: A Comprehensive Guide

Need a clear and practical understanding of the OBD2 protocol, specifically for your 2008 BMW?

This guide provides an in-depth introduction to the On-Board Diagnostics (OBD2) protocol, focusing on its relevance to 2008 BMW models. We’ll explore the OBD2 connector, OBD2 Parameter IDs (PIDs), and its connection to the CAN bus system, all within the context of your BMW.

Note: This is designed as a comprehensive and practical guide, so you’ll learn not only the theory but also how to access and interpret OBD2 data from your 2008 BMW, understand key applications, and gain valuable troubleshooting tips.

Discover why this is becoming the go-to resource for understanding the OBD2 system in 2008 BMWs and similar vehicles.

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

Article Contents:

Author: Martin Falch (updated January 2025)

Download this guide as a PDF

Understanding OBD2 in Your 2008 BMW

OBD2 is essentially the health monitor for your 2008 BMW. It’s an integrated self-diagnostic system designed to track vehicle performance and emissions. As a standardized protocol, OBD2 enables the extraction of Diagnostic Trouble Codes (DTCs) and real-time operational data via the OBD2 port, which is a crucial tool for diagnosing any issues in your BMW.

You’ve likely already encountered OBD2 in action, especially if you’ve seen the check engine light illuminate on your BMW’s dashboard.

This light is your BMW’s way of signaling a potential problem. When this happens, a mechanic will typically use an OBD2 scanner to pinpoint the issue. For 2008 BMW models, this process is standardized:

The mechanic connects the OBD2 scanner to the standard 16-pin OBD2 connector, usually located beneath the steering column in your BMW. This tool sends ‘OBD2 requests’ to the car’s computer, and the BMW responds with ‘OBD2 responses’. These responses can include vital data such as engine speed, fuel levels, and those all-important Diagnostic Trouble Codes (DTCs). This streamlined communication drastically speeds up the troubleshooting and repair process for your 2008 BMW.

OBD2 Compatibility: Is Your 2008 BMW Equipped?

The good news is: Yes, your 2008 BMW is almost certainly OBD2 compliant.

By 2008, OBD2 was a mandated standard in the United States for all vehicles. BMW, adhering to these regulations, ensured that their 2008 models were fully compliant with the ISO 15765-4 standard, which specifies CAN (Controller Area Network) as the communication backbone for OBD2 systems.

While virtually all 2008 BMWs sold in major markets will support OBD2, it’s worth noting that older vehicles, even with a 16-pin connector, might not fully support the OBD2 protocol. However, for a 2008 BMW, you can be confident in its OBD2 compliance due to the regulatory timelines.

To be absolutely certain, you can usually check your vehicle’s manual or look for an OBD2 compliance sticker, often found under the hood. However, given the 2008 manufacturing year and BMW’s market compliance, OBD2 support is a near certainty.

The Evolution of OBD2: Key Milestones for Your BMW Era

The history of OBD2 is rooted in environmental consciousness, originating in California. The California Air Resources Board (CARB) was the driving force, requiring OBD systems in all new cars from 1991 onwards for effective emission control.

The Society of Automotive Engineers (SAE) played a crucial role in standardizing OBD2, especially the Diagnostic Trouble Codes (DTCs) and the physical OBD connector, ensuring uniformity across different manufacturers (SAE J1962).

The OBD2 standard rollout was a phased process, directly impacting vehicles like your 2008 BMW:

1996: OBD2 became mandatory in the USA for all cars and light trucks.
2001: The EU mandated OBD2 for gasoline cars.
2003: EU extended the mandate to include diesel cars (EOBD – European On-Board Diagnostics).
2005: OBD2 requirement expanded in the US to medium-duty vehicles.
2008: A pivotal year for your 2008 BMW, as US vehicles were required to adopt ISO 15765-4 (CAN) as the foundation for OBD2 communication. This standardization is critical for how tools interface with your BMW’s diagnostic system.
2010: OBD2 mandates were finalized in the US for heavy-duty vehicles.

This historical timeline underscores why your 2008 BMW utilizes the CAN-based OBD2 protocol, ensuring standardized diagnostics and emissions monitoring.

The Future of OBD2 and Implications for BMW Diagnostics

OBD2’s role is set to evolve, but its fundamental importance remains, though its future form is subject to change.

Originally legislated for emissions control and testing, OBD2’s relevance is being reconsidered with the rise of electric vehicles. Interestingly, electric vehicles are not currently required to support OBD2 in the same way, and many modern EVs do not implement standard OBD2 requests. Instead, they often use OEM-specific UDS (Unified Diagnostic Services) communication protocols. This shift can make accessing data from EVs challenging without specific reverse-engineered protocols, as seen in case studies for brands like Tesla, Hyundai/Kia, Nissan, and VW/Skoda EVs.

Considering the limitations of current OBD2 implementations in terms of data richness and protocol flexibility, newer standards like WWH-OBD (World Wide Harmonized OBD) and OBDonUDS (OBD on UDS) are emerging. These aim to modernize OBD communication by using the UDS protocol as a base, offering enhanced diagnostic capabilities. For a deeper dive into these protocols, refer to our introduction to UDS.

In our increasingly connected world, traditional OBD2 testing methods are becoming less efficient. Manual emission checks are time-consuming and costly, paving the way for OBD3 – the integration of telematics into all vehicles.

OBD3 envisions adding a small radio transponder to vehicles, similar to those used for electronic toll collection. This would allow for the automatic transmission of the car’s Vehicle Identification Number (VIN) and DTCs via WiFi to a central server for real-time monitoring and diagnostics.

Technologies to facilitate CAN or OBD2 data transfer via WiFi/cellular are already available, such as the CANedge2 WiFi CAN logger and the CANedge3 3G/4G CAN logger. While offering convenience and cost savings, OBD3 also raises political and privacy concerns related to increased vehicle surveillance.

While OBD2 was initially designed for in-garage emission testing, it’s now extensively used by third parties for real-time data acquisition via OBD2 dongles, CAN loggers and similar devices. However, the German car industry is considering restricting this third-party access.

BMW, among other manufacturers, has expressed concerns about unauthorized data access:

“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 involves potentially disabling OBD2 functionality during normal driving, centralizing data collection through manufacturer-controlled servers. This would give manufacturers greater control over ‘automotive big data’ and could enhance security by reducing the risk of car hacking. However, many view this move with skepticism, seeing it as a commercially motivated strategy to control vehicle data, which could significantly disrupt the market for third-party OBD2 services (viewpoint on OBD trackers). Whether this trend gains traction remains to be seen, but it signifies a potential shift in how vehicle data is accessed and utilized.

Deep Dive into CAN Bus with Our Ultimate Guide

Ready to become a CAN bus expert and better understand your BMW’s OBD2 system?

Our comprehensive ‘Ultimate CAN Guide’ compiles 12 ‘simple intros’ into a 160+ page PDF:

Download the Ultimate CAN Guide Now

OBD2 Standards: Ensuring Compatibility for Your 2008 BMW

On-board diagnostics, or OBD2, is a higher-layer protocol, much like a language that vehicles use to communicate diagnostic information. CAN, on the other hand, is the communication method or ‘phone line’ used for this communication. This makes OBD2 comparable to other CAN-based higher-layer protocols such as J1939, CANopen, and NMEA 2000. For your 2008 BMW, understanding these standards is key to effective diagnostics and data interpretation.

OBD2 standards specifically define the OBD2 connector, the lower-layer communication protocols, OBD2 Parameter IDs (PIDs), and much more. These standards are structured within a 7-layer OSI model, and in the following sections, we’ll focus on the standards most relevant to your 2008 BMW and OBD2 diagnostics.

In the OSI model context, you’ll notice that both SAE (Society of Automotive Engineers) and ISO (International Organization for Standardization) standards are referenced. This reflects the global nature of OBD2 standardization, with SAE standards originating from the US and ISO standards more broadly adopted internationally, including in Europe where BMW is based. Many of these standards are technically very similar; for example, SAE J1979 is functionally equivalent to ISO 15031-5, and SAE J1962 mirrors ISO 15031-3. For 2008 BMW models, compliance with ISO standards, particularly ISO 15765 for CAN-based OBD2, is paramount.

The OBD2 Connector: Accessing Your 2008 BMW’s Data [SAE J1962]

The 16-pin OBD2 connector is your direct interface for accessing diagnostic data from your 2008 BMW. This connector is standardized under SAE J1962 / ISO 15031-3, ensuring uniformity across vehicles.

The illustration above details a Type A OBD2 pin connector, often referred to as the Data Link Connector (DLC). Here are key points to consider when working with your 2008 BMW’s OBD2 port:

You’ll typically find the connector near the steering wheel, though its exact location can sometimes be hidden behind a panel.
Pin 16 is crucial as it supplies battery power, often remaining active even when the ignition is off, which is important for diagnostic tools that need constant power.
The specific OBD2 pinout configuration depends on the communication protocol used by the vehicle.
For 2008 BMW models, and most modern cars, the lower-layer protocol is CAN bus. This means pins 6 (CAN-High) and 14 (CAN-Low) are the primary data communication lines.

OBD2 Connector Types: Type A vs. Type B

While working with OBD2 systems, particularly if you’re involved with a range of vehicles, you might encounter both Type A and Type B OBD2 connectors. Type A is standard in most cars, including your 2008 BMW, while Type B is more common in medium and heavy-duty vehicles.

As shown in the illustration, both types share similar pin assignments but differ in power supply outputs. Type A typically provides 12V, suitable for cars, while Type B is designed for 24V systems found in larger vehicles. The data communication baud rates can also vary, with cars like your BMW commonly using 500K, whereas heavy-duty vehicles often use 250K (though newer models may also support 500K).

A key physical difference is that the Type B OBD2 connector has a break in the center groove. This design feature means that a Type B OBD2 adapter cable is universally compatible with both Type A and Type B sockets, but a Type A connector will not fit into a Type B socket. However, for your 2008 BMW, you will only need to be concerned with Type A connectors.

OBD2 and CAN Bus: The ISO 15765-4 Standard in 2008 BMWs

Since 2008, CAN bus has been the mandatory lower-layer protocol for OBD2 in all vehicles sold in the US, as mandated by ISO 15765. This is directly relevant to your 2008 BMW, as it will use CAN bus for OBD2 communication.

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

Specifically, ISO 15765-4 standardizes the CAN interface for diagnostic equipment, focusing on the physical, data link, and network layers:

The CAN bus bit rate must be either 250K or 500K. For your 2008 BMW, it’s highly likely to be 500K, which is common for passenger vehicles.
CAN IDs can be 11-bit or 29-bit. BMWs, like most cars, typically use 11-bit CAN IDs for OBD2.
Specific CAN IDs are reserved for OBD requests and responses, ensuring standardized communication.
The diagnostic CAN frame data length is fixed at 8 bytes, optimizing data transmission efficiency.
The OBD2 adapter cable is limited to a maximum length of 5 meters to maintain signal integrity.

OBD2 CAN Identifiers: 11-bit and 29-bit Addressing

OBD2 communication over CAN bus, in your 2008 BMW, relies on a request-response messaging system.

Most cars, including BMW models from 2008, utilize 11-bit CAN IDs for OBD2 communication. In this setup, the ‘Functional Addressing’ ID is 0x7DF. This ID is used to broadcast a request to all OBD2-compliant Electronic Control Units (ECUs) in the vehicle, asking if they have data related to the requested parameter (as per ISO 15765-4). Alternatively, ‘Physical Addressing’ can be used with CAN IDs ranging from 0x7E0 to 0x7E7 to direct requests to specific ECUs, although this is less commonly used in standard OBD2 diagnostics.

ECUs respond using 11-bit IDs in the range of 0x7E8 to 0x7EF. The most frequently used response ID is 0x7E8, which typically comes from the ECM (Engine Control Module), and to a lesser extent, 0x7E9 from the TCM (Transmission Control Module). When diagnosing your 2008 BMW, you’ll primarily see responses on these IDs.

In some vehicle types, such as vans and medium to heavy-duty vehicles, you might encounter OBD2 communication using extended 29-bit CAN identifiers instead of the standard 11-bit. However, this is not typical for passenger cars like your 2008 BMW.

For 29-bit CAN, the ‘Functional Addressing’ CAN ID is 0x18DB33F1. Responses in this format range from CAN IDs 0x18DAF100 to 0x18DAF1FF (commonly 18DAF110 and 18DAF11E). This response ID format is sometimes also presented in the ‘J1939 PGN’ form, specifically PGN 0xDA00 (55808), which is designated in the J1939-71 standard as ‘Reserved for ISO 15765-2’. While less relevant for your BMW, understanding both 11-bit and 29-bit formats is useful for broader diagnostic work.

OBD2 vs. BMW Proprietary CAN Protocols

It’s crucial to understand that the Electronic Control Units (ECUs) in your 2008 BMW, and in all vehicles, primarily operate using proprietary CAN protocols defined by BMW, not OBD2. OBD2 is an additional, standardized protocol layered on top for diagnostic and emissions-related data access. BMW’s proprietary CAN protocols are specific to their brand, models, and production years, handling core vehicle functions. This data is generally inaccessible to those outside of BMW without significant reverse engineering effort (CAN bus reverse engineering techniques).

If you connect a CAN bus data logger to your 2008 BMW’s OBD2 port, you might observe OEM-specific CAN data alongside OBD2 data, typically broadcast at high rates (1000-2000 frames/second). However, in many newer vehicles, including some 2008 models and onwards, a ‘gateway’ module might restrict access to this proprietary CAN data via the OBD2 port, allowing only standardized OBD2 communication.

In essence, think of OBD2 as a separate, ‘add-on’ higher-layer protocol that runs in parallel with BMW’s internal, proprietary communication network. It’s designed for diagnostics and mandated emissions data, not for accessing the full spectrum of vehicle operational data typically used by the manufacturer.

Bit-Rate and ID Validation for OBD2 on BMW

As previously noted, OBD2 over CAN can use two bit rates (250K, 500K) and two CAN ID lengths (11-bit, 29-bit). This results in four potential protocol combinations. For your 2008 BMW, the most common configuration is 500K bit rate with 11-bit CAN IDs. However, diagnostic tools should ideally perform an auto-detection process to confirm the correct settings.

ISO 15765-4 provides guidelines for a systematic initialization sequence to determine the correct protocol combination. This process leverages the fact that OBD2 compliant vehicles must respond to a specific mandatory OBD2 request (detailed in the OBD2 PID section). Incorrect bit rate settings will result in CAN error frames, which diagnostic tools can detect to adjust settings.

Newer versions of ISO 15765-4 also account for vehicles that may support OBD communication via OBDonUDS (OBD on Unified Diagnostic Services) rather than the more traditional OBDonEDS (OBD on Emission Diagnostic Service). This article primarily focuses on OBD2/OBDonEDS (as per ISO 15031-5/SAE J1979), which is typical for most non-electric vehicles including your 2008 BMW, as opposed to WWH-OBD/OBDonUDS (as per ISO 14229, ISO 27145-3/SAE J1979-2), which is more common in EU trucks and buses.

To differentiate between OBDonEDS and OBDonUDS protocols, advanced diagnostic tools may send additional UDS requests using 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. However, for a 2008 BMW, it is highly likely to use OBDonEDS.

Five Lower-Layer OBD2 Protocols: Beyond CAN for Older Vehicles

While CAN (ISO 15765) is the dominant lower-layer protocol for OBD2 in modern vehicles, including your 2008 BMW, it’s helpful to be aware of the other four protocols that were used in older vehicles (pre-2008). If you are working with older BMW models or other pre-2008 vehicles, understanding these protocols can be beneficial. Note the pinouts of the OBD2 connector can sometimes indicate which protocol is in use.

ISO 15765 (CAN bus): As discussed, this is mandatory in US cars since 2008 and is widely used today, including in your 2008 BMW.
ISO14230-4 (KWP2000): The Keyword Protocol 2000 was common in 2003 and later cars, particularly in Asia and Europe, but not typically in BMWs of the 2008 era.
ISO 9141-2: Used in EU, Chrysler, and Asian cars around 2000-2004. Less likely to be found in a 2008 BMW.
SAE J1850 (VPW): Predominantly used in older GM vehicles.
SAE J1850 (PWM): Mostly found in older Ford vehicles.

For diagnosing your 2008 BMW, focusing on CAN bus (ISO 15765) is the most relevant approach.

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

All OBD2 data communication, including in your 2008 BMW, over CAN bus uses the ISO-TP (ISO 15765-2) transport protocol. This protocol is essential because it allows for the transmission of data payloads larger than the 8-byte limit of a standard CAN frame. This capability is necessary in OBD2 for operations like retrieving the Vehicle Identification Number (VIN) or Diagnostic Trouble Codes (DTCs), which often require more than 8 bytes of data. ISO 15765-2 handles segmentation of larger messages, flow control to manage data exchange, and reassembly of segmented messages. For a more detailed explanation, refer to our introduction to UDS protocol.

However, for many standard OBD2 parameters, the data 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 – Protocol Control Information) indicates the payload length, excluding any padding. This leaves up to 7 bytes available for the actual OBD2 communication data.

The OBD2 Diagnostic Message Structure [SAE J1979, ISO 15031-5]

To effectively work with OBD2 data on a CAN bus system, like in your 2008 BMW, it’s important to understand the structure of a raw ‘Single Frame’ OBD2 CAN message. In simplified terms, an OBD2 message consists of a CAN identifier, a data length indicator (PCI field), and the data payload. The payload itself is further structured into a Mode byte, a Parameter ID (PID), and data bytes.

Example: OBD2 Request and Response Sequence

Let’s illustrate with an example of requesting and receiving ‘Vehicle Speed’ data from your 2008 BMW.

An external diagnostic tool initiates a request by sending a CAN message with the ID 0x7DF and a 2-byte payload: Mode 0x01 and PID 0x0D. This is a standardized request for vehicle speed. Your BMW’s ECU (likely the ECM) then responds with a CAN message using ID 0x7E8 and a 3-byte payload. This payload includes the requested Vehicle Speed value in the fourth byte of the CAN data frame, in this example, 0x32 (which is 50 in decimal).

By consulting the OBD2 PID specifications for PID 0x0D, we can determine the scaling and units to convert the raw byte value (0x32) into a physical value. In this case, 50 corresponds to 50 km/h.

Next, we’ll delve deeper into OBD2 Modes and Parameter IDs (PIDs) which are fundamental to interpreting OBD2 data from your 2008 BMW.

The 10 Standard OBD2 Services (Modes)

OBD2 defines 10 diagnostic services, often referred to as ‘modes’, which are used to request different types of diagnostic information. Mode 0x01 is commonly used to retrieve current, real-time data parameters, while other modes are designed to access and clear Diagnostic Trouble Codes (DTCs), retrieve freeze frame data, and perform other diagnostic functions. Understanding these modes is essential for effectively using OBD2 with your 2008 BMW.

It’s important to note that not all vehicles are required to support all 10 OBD2 modes. Manufacturers can also implement additional, OEM-specific OBD2 modes beyond the 10 standardized ones.

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).

OBD2 Parameter IDs (PIDs): Requesting Specific Data from Your BMW

Within each OBD2 service mode, Parameter IDs (PIDs) are used to specify the exact data parameter being requested. For example, in Mode 0x01 (Show Current Data), there are approximately 200 standardized PIDs that can provide real-time data on parameters like vehicle speed, engine RPM, coolant temperature, and fuel level. However, a vehicle, including your 2008 BMW, is not required to support all PIDs within a given mode. In practice, most vehicles support only a subset of the available PIDs.

One PID is particularly significant for OBD2 compatibility testing:

Specifically, if an emissions-related ECU in your 2008 BMW supports any OBD2 services, it must support Mode 0x01 PID 0x00. When PID 0x00 is requested in Mode 0x01, the vehicle’s ECU responds by indicating which PIDs in the range 0x01-0x20 it supports. This makes PID 0x00 a fundamental ‘OBD2 compatibility check’. Similarly, PIDs 0x20, 0x40, 0x60, 0x80, 0xA0, and 0xC0 are used to determine support for subsequent blocks of PIDs within Mode 0x01 (0x21-0x40, 0x41-0x60, etc.).

Tip: Utilizing an OBD2 PID Overview Tool

The appendices of SAE J1979 and ISO 15031-5 provide detailed scaling and conversion formulas for standard OBD2 PIDs. This information is essential for converting raw data bytes into meaningful physical values, as explained in our CAN bus introduction guide.

To simplify working with Mode 0x01 PIDs for your 2008 BMW or any OBD2 vehicle, consider using our OBD2 PID overview tool. This tool helps you construct OBD2 request frames and dynamically decode OBD2 responses, making the diagnostic process more efficient and accurate.

Access the OBD2 PID overview tool

Practical Guide: Logging and Decoding OBD2 Data from Your BMW

In this section, we’ll provide a practical example of how to log OBD2 data from your 2008 BMW using a CANedge CAN bus data logger. The CANedge is versatile and allows configuration of custom CAN frames for transmission, making it ideal for OBD2 data logging and analysis.

To get started, you’ll need to connect the CANedge to your BMW. This is easily done using our OBD2-DB9 adapter cable, which provides a direct interface between the logger and your vehicle’s OBD2 port.

Example of sending a CAN frame at 500K to validate bit-rate

Reviewing ‘Supported PIDs’ responses in asammdf software

Step #1: Bit-Rate, ID, and Supported PIDs Verification

As discussed earlier, ISO 15765-4 outlines a procedure to determine the correct bit-rate and CAN IDs for OBD2 communication with a vehicle. You can use the CANedge to systematically test these parameters for your 2008 BMW, as detailed below (refer to the CANedge Intro for setup specifics):

Bit-rate Test: Begin by attempting to send a CAN frame at 500K bit/s. Monitor if the transmission is successful. If not, try 250K bit/s. For a 2008 BMW, 500K is the expected rate.
Bit-rate Confirmation: Once successful transmission is established at a bit-rate, use this rate for all subsequent communication.
‘Supported PIDs’ Request: Send multiple ‘Supported PIDs’ requests (Mode 0x01, PIDs 0x00, 0x20, 0x40, etc.) to your BMW.
Response Analysis: Review the responses received from your BMW in software like asammdf.
Protocol Determination: Based on the response CAN IDs (e.g., 0x7E8, 0x7E9), determine whether your BMW is using 11-bit or 29-bit CAN IDs for OBD2. Typically, 11-bit IDs are used.
PID Support Identification: Analyze the response data to identify which specific PIDs are supported by your 2008 BMW.

We provide pre-configured CANedge settings to streamline these tests.

Most 2008 and newer non-electric vehicles support a range of 40-80 PIDs using a 500K bit/s rate, 11-bit CAN IDs, and the standard OBD2/OBDonEDS protocol.

As illustrated in the asammdf screenshot, you may observe multiple responses to a single OBD request, particularly when using the functional request ID 0x7DF. This occurs because the 0x7DF ID polls all ECUs for a response. Since all OBD2/OBDonEDS-compliant ECUs must support service 0x01 PID 0x00, you often get multiple responses to this PID. As you request subsequent ‘Supported PIDs’ (0x20, 0x40, etc.), fewer ECUs may respond, indicating varied PID support across different modules. Notice that the ECM ECU (0x7E8) often supports all PIDs supported by other ECUs in this example. To reduce bus load, you can switch to ‘Physical Addressing’ using CAN ID 0x7E0 for subsequent requests, targeting only the ECM for responses.

Step #2: Configuring OBD2 PID Requests for Targeted Data Logging

After determining the supported OBD2 PIDs for your 2008 BMW, and confirming the bit-rate and CAN ID settings, you can configure the CANedge to specifically request the PIDs of interest.

Consider these factors when setting up your PID request list:

CAN ID Strategy: Switch from ‘Functional Addressing’ (0x7DF) to ‘Physical Addressing’ request IDs (e.g., 0x7E0 for ECM) to minimize redundant responses and bus load.
Request Spacing: Implement a delay of 300-500 milliseconds between consecutive OBD2 requests. Rapidly spamming requests can overwhelm ECUs and lead to unreliable responses.
Power Management: Utilize triggers in your CANedge configuration to halt data transmission when the vehicle is inactive. This prevents unnecessary battery drain and avoids ‘waking up’ ECUs when the vehicle is off.
Data Filtering: Set up filters on the CANedge to record only OBD2 response messages. This is especially useful if your BMW also broadcasts OEM-specific CAN data, allowing you to focus solely on the diagnostic information.

Once configured, your CANedge is ready to log raw OBD2 data from your 2008 BMW efficiently!

Example transmit list of CANedge OBD2 PID requests

Visualizing DBC decoded OBD2 data in asammdf

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

Finally, to effectively analyze and visualize the logged raw OBD2 data from your 2008 BMW, you need to decode it into physical, understandable values (like km/h for speed, °C for temperature). This decoding process relies on the specifications defined in ISO 15031-5/SAE J1979 and resources like Wikipedia.

To simplify this process, we offer a free OBD2 DBC file. This DBC file allows you to easily DBC decode the raw OBD2 data within most standard CAN bus software tools, including asammdf.

Decoding OBD2 data is somewhat 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 determine the specific signal within the payload.

To accurately decode OBD2 data, you must consider not only the CAN ID but also the OBD2 mode and PID. This technique is known as ‘extended multiplexing‘. It’s a method where the data’s meaning is determined by a combination of identifiers, which can be effectively implemented using DBC files and supporting software. Our provided OBD2 DBC file is structured to handle this extended multiplexing, making data interpretation straightforward.

CANedge: Your OBD2 Data Logging Solution

The CANedge is designed for easy OBD2 data recording. It logs data directly to a removable 8-32 GB SD card. Simply connect it to your 2008 BMW or other vehicle to begin logging. Data can then be decoded and analyzed using free software and APIs along with our OBD2 DBC file.

Learn more about OBD2 logging

Explore CANedge data logger features

OBD2 Multi-Frame Communication Examples [ISO-TP]

As discussed, OBD2 communication leverages ISO-TP (ISO 15765-2) for handling messages, including those exceeding 8 bytes, known as multi-frame messages. Most examples so far have focused on single-frame communication. This section provides examples of multi-frame communication, which is essential for retrieving larger datasets like VIN or DTCs from your 2008 BMW.

Multi-frame OBD2 communication involves flow control frames to manage the data exchange (see our UDS introduction). In practice, flow control can be implemented by transmitting a static flow control frame approximately 50 milliseconds after the initial request frame, as demonstrated in the CANedge configuration example provided.

Analyzing multi-frame OBD2 responses requires CAN software and API tools that support ISO-TP, such as the CANedge MF4 decoders. These tools are capable of reassembling segmented messages and correctly interpreting the data.

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

The Vehicle Identification Number (VIN) is crucial for vehicle identification in telematics, diagnostics, and more (see our UDS introduction for further details). To retrieve the VIN from your 2008 BMW using OBD2, you would use Mode 0x09 and PID 0x02.

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

The vehicle responds with a First Frame. This frame includes the PCI, total message length (0x014 = 20 bytes), mode (0x49, i.e., 0x09 + 0x40), and PID (0x02). Following the PID, you’ll find the byte 0x01, which represents the Number Of Data Items (NODI), in this case, indicating a single VIN. The subsequent 17 bytes contain the VIN itself, encoded in HEX. This HEX representation can be converted to ASCII characters to reveal the VIN, using methods described in our UDS introduction.

Example 2: OBD2 Multi-PID Request (Requesting 6 PIDs Simultaneously)

OBD2 allows diagnostic tools to request up to 6 Mode 0x01 PIDs in a single request frame. The vehicle’s ECU should respond with data for all supported PIDs from the request (omitting data for unsupported PIDs). If necessary, responses can span multiple frames using ISO-TP.

This feature enhances data collection efficiency, allowing for higher-frequency data sampling. However, the signal encoding becomes specific to the request method, which can complicate the use of generic OBD2 DBC files. For this reason, this method is generally not recommended for practical logging unless you have tools specifically designed for it. Here’s an example trace of such a communication sequence:

The multi-frame response structure is similar to the VIN example, but the payload includes both the requested PIDs and their corresponding data. In practice, the PIDs in the response are often ordered as they were requested, though this is not strictly mandated by the ISO 15031-5 standard.

Decoding these multi-PID responses using generic DBC files is challenging because the data encoding is highly multiplexed and depends on the specific PIDs requested and their order. A DBC file would need to account for the variable position of each PID in the payload, making it difficult to generalize across different vehicles or requests. Furthermore, if you send multiple such multi-PID requests, distinguishing between responses becomes complex without a sophisticated decoding strategy.

While custom scripts and recording request messages alongside responses can help in specific scenarios, this approach is not scalable or practical for general OBD2 data logging and analysis, especially when compared to requesting single PIDs in separate requests.

Example 3: Retrieving OBD2 Diagnostic Trouble Codes (DTCs)

You can use OBD2 Mode 0x03, ‘Show stored Diagnostic Trouble Codes’, to request emissions-related DTCs from your 2008 BMW. For this request, no PID is included in the request message itself. The targeted ECU(s) will respond with the number of DTCs currently stored (which could be zero if no DTCs are active), with each DTC encoded in 2 data bytes. Multi-frame responses are necessary if more than 2 DTCs are stored because of the data size.

The 2-byte DTC value is structured as defined in ISO 15031-5/ISO 15031-6. The first 2 bits indicate the DTC category (e.g., Powertrain, Chassis, Body, Network), and the remaining 14 bits form a 4-digit code (displayed in hexadecimal). Decoded DTC values can be looked up using OBD2 DTC lookup tools like repairpal.com to understand the specific issue indicated by the code.

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

OBD2 Data Logging: Practical Use Case Examples

OBD2 data from cars and light trucks, including your 2008 BMW, is valuable for a variety of applications:

Vehicle Data Logging for Cars:

OBD2 data logging in cars can be applied to reduce fuel consumption, improve driving habits, test prototype vehicle components, and for insurance telematics applications.

Explore OBD2 loggers

Real-Time Vehicle Diagnostics:

OBD2 interfaces enable real-time streaming of vehicle data, which is crucial for diagnosing vehicle issues as they occur. This is particularly useful in repair shops for quick and accurate troubleshooting.

Learn about OBD2 streaming

Predictive Maintenance Applications:

By continuously monitoring OBD2 data via IoT-connected OBD2 loggers, potential breakdowns in cars and light trucks can be predicted and prevented. This is valuable for fleet management and vehicle maintenance scheduling.

Discover predictive maintenance solutions

Vehicle Black Box Recording:

An OBD2 logger can serve as a ‘black box’ in vehicles or equipment, continuously recording data that can be vital in the event of disputes, accidents, or for in-depth diagnostics after an incident.

Explore CAN bus black box loggers

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

For more introductory guides and tutorials, visit our guides section or download our comprehensive ‘Ultimate Guide’ PDF.

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