Decoding OBD2 Signals: Your Practical Guide to On-Board Diagnostics

Need a straightforward and practical understanding of Obd2 Signals?

This guide provides a comprehensive introduction to the world of On-Board Diagnostics (OBD2) signals, covering everything from the OBD2 connector and Parameter IDs (PIDs) to their link with the CAN bus.

This isn’t just a theoretical overview; we’ll equip you with the knowledge to request and decode OBD2 data, explore key logging applications, and offer practical tips for working with OBD2 signals.

Discover why this guide is becoming the go-to resource for understanding OBD2 signals.

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

Understanding OBD2 Signals: An Overview

OBD2, or On-Board Diagnostics version 2, is essentially your car’s internal health monitoring system. It’s a standardized protocol designed to output OBD2 signals, which are used to extract diagnostic trouble codes (DTCs) and access real-time vehicle data through the OBD2 connector. These OBD2 signals are the language your car uses to communicate its status and potential issues.

You’ve likely already encountered the concept of OBD2 signals, perhaps indirectly:

Ever seen the malfunction indicator light, commonly known as the “check engine light,” illuminate on your dashboard?

That light is triggered by OBD2 signals, indicating that your car has detected a problem. When you take your vehicle to a mechanic, they use an OBD2 scanner to interpret these OBD2 signals and diagnose the issue.

Mechanics connect an OBD2 reader to the 16-pin OBD2 connector, typically located near the steering wheel. This tool sends ‘OBD2 requests’ to the car, prompting it to respond with ‘OBD2 responses’. These responses, composed of OBD2 signals, can contain a wealth of information, including speed, fuel level, and Diagnostic Trouble Codes (DTCs). By analyzing these OBD2 signals, mechanics can efficiently troubleshoot problems.

OBD2 Compatibility: Does Your Car Speak OBD2 Signals?

The question is: Does your car utilize OBD2 signals?

The short answer: Almost certainly, yes!

The vast majority of modern, non-electric vehicles are OBD2 compliant and predominantly communicate using the CAN bus protocol to transmit OBD2 signals. However, for older vehicles, the presence of a 16-pin OBD2 connector doesn’t guarantee OBD2 support. Some older cars may have the connector but not fully implement the OBD2 standard. To confirm compatibility, consider the vehicle’s origin and year of purchase:

A Brief History of OBD2 and the Rise of Standardized Signals

The story of OBD2 signals begins in California. The California Air Resources Board (CARB) mandated OBD in all new cars from 1991 onwards, primarily for emission control. This marked the initial push towards standardized OBD2 signals for environmental monitoring.

The Society of Automotive Engineers (SAE) further developed the standard, leading to standardized DTCs and the OBD connector, documented in SAE J1962. This standardization was crucial for ensuring that OBD2 signals could be universally interpreted across different manufacturers.

The adoption of the OBD2 standard, and therefore the use of OBD2 signals, was gradually implemented:

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

The Future of OBD2 Signals: Trends and Transformations

OBD2 and OBD2 signals are firmly established, but how will they evolve?

Here are key trends shaping the future of OBD and OBD2 signals:

Originally designed for emissions testing, legislated OBD2 has a limited scope. Notably, electric vehicles (EVs) are not obligated to support OBD2 in any form. This is reflected in the fact that most modern EVs do not support standard OBD2 signal requests. Instead, they often use OEM-specific UDS communication protocols. This makes accessing OBD2 signals from EVs challenging, except when reverse engineering efforts uncover the decoding methods, as seen in case studies for electric cars like Tesla, Hyundai/Kia, Nissan, and VW/Skoda EVs.

Current OBD2 implementations have limitations, particularly in data richness and lower-layer protocols for transmitting OBD2 signals. Modern alternatives like WWH-OBD (World Wide Harmonized OBD) and OBDonUDS (OBD on UDS) are emerging to address these issues. These protocols aim to enhance OBD communication and the quality of OBD2 signals by using the UDS protocol as a base. Learn more about these protocols in our intro to UDS.

In our increasingly connected world, manual OBD2 emission checks seem outdated. The solution? OBD3 – integrating telematics into all vehicles, promising a shift in how OBD2 signals are utilized.

OBD3 envisions adding a small radio transponder to all cars, similar to those used for bridge tolls. This would allow the car’s Vehicle Identification Number (VIN) and DTCs to be transmitted wirelessly via WiFi to a central server for automated checks. This would revolutionize the way OBD2 signals are collected and used for regulatory purposes.

Many devices already enable wireless transmission of CAN or OBD2 data, such as the CANedge2 WiFi CAN logger and the CANedge3 3G/4G CAN logger. These devices highlight the growing trend of leveraging wireless technology to access and utilize OBD2 signals.

While convenient and cost-saving, OBD3 also raises political challenges related to surveillance concerns, as continuous transmission of OBD2 signals could be perceived as an invasion of privacy.

The original purpose of OBD2 was for stationary emission controls. However, today, third parties extensively use OBD2 signals for real-time data generation through OBD2 dongles, CAN loggers, and similar devices. However, the German car industry is seeking to change this landscape:

OBD was designed for car servicing in repair shops, not for third parties to build a data-driven economy on the access provided by this interface.

– Christoph Grote, SVP Electronics, BMW (2017)

The proposal is to disable OBD2 functionality while driving and instead collect data on a central server. This would give manufacturers control over ‘automotive big data’ derived from OBD2 signals.

The rationale is security, aiming to reduce the risk of car hacking. However, many view this as a commercially motivated move. Whether this trend gains traction remains to be seen, but it could significantly disrupt the market for third-party services that rely on OBD2 signals.

Become a CAN Bus Expert with Our ‘Ultimate CAN Guide’

Want to master CAN bus technology and deepen your understanding of how OBD2 signals are transmitted?

Our comprehensive 160+ page PDF guide offers 12 ‘simple intros’ to CAN bus concepts, providing essential context for understanding OBD2 signals.

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OBD2 Standards: Defining the Language of OBD2 Signals

On-board diagnostics, OBD2, operates as a higher layer protocol, similar to a language, in the context of vehicle communication. CAN, on the other hand, serves as the communication method, like a telephone line. This makes OBD2 comparable to other CAN-based higher-layer protocols such as J1939, CANopen, and NMEA 2000. All of these protocols, including OBD2, rely on structured signals to transmit information.

The OBD2 standards specifically define the OBD2 connector, lower-layer protocols, OBD2 Parameter IDs (PIDs), and the structure and interpretation of OBD2 signals.

These standards can be visualized using a 7-layer OSI model. In the following sections, we’ll focus on the most critical aspects relevant to understanding OBD2 signals.

In the OSI model overview, you’ll notice that both SAE and ISO standards cover multiple layers. This reflects the standardization of OBD in the USA (SAE) and EU (ISO). Many standards are technically similar, for instance, SAE J1979 and ISO 15031-5, and SAE J1962 and ISO 15031-3, both contributing to the consistent interpretation of OBD2 signals.

The OBD2 Connector: Your Gateway to OBD2 Signals [SAE J1962]

The 16-pin OBD2 connector, defined by SAE J1962 / ISO 15031-3, provides easy access to your car’s data and is the physical interface through which OBD2 signals are transmitted and received.

The illustration shows a Type A OBD2 pin connector (also known as the Data Link Connector, DLC). This connector is the point of entry for accessing and interpreting OBD2 signals.

Key points about the OBD2 connector:

It’s usually located near the steering wheel, but it might be hidden from plain sight.
Pin 16 provides battery power, often even when the ignition is off, ensuring continuous power for devices monitoring OBD2 signals.
The OBD2 pinout configuration depends on the communication protocol used for transmitting OBD2 signals.
CAN bus is the most prevalent lower-layer protocol, meaning pins 6 (CAN-H) and 14 (CAN-L) are typically connected for transmitting OBD2 signals.

OBD2 Connector Types: A vs. B

You might encounter both Type A and Type B OBD2 connectors. Type A is commonly found in cars, while Type B is more prevalent in medium and heavy-duty vehicles. Both types are designed to handle OBD2 signals, but they differ in power supply and application.

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, with cars typically using 500K and heavy-duty vehicles often using 250K (with increasing support for 500K). These variations impact the transmission of OBD2 signals.

Type B OBD2 connectors have an interrupted groove in the middle for physical differentiation. 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 is designed to ensure correct signal and power handling.

OBD2 and CAN Bus: The Foundation for OBD2 Signals [ISO 15765-4]

Since 2008, CAN bus has been the mandatory lower-layer protocol for OBD2 in all US cars, as per ISO 15765. This means that OBD2 signals are primarily transmitted over the CAN bus network in modern vehicles.

ISO 15765-4 (Diagnostics over CAN or DoCAN) specifies restrictions applied to the CAN standard (ISO 11898) for OBD2. These restrictions ensure reliable and standardized transmission of OBD2 signals.

Specifically, it standardizes the CAN interface for test equipment, focusing on the physical, data link, and network layers to ensure consistent OBD2 signals:

CAN bus bit-rate must be either 250K or 500K, defining the speed of OBD2 signal transmission.
CAN IDs can be 11-bit or 29-bit, influencing the addressing of OBD2 signals on the network.
Specific CAN IDs are designated for OBD requests/responses, structuring the flow of OBD2 signals.
Diagnostic CAN frame data length is fixed at 8 bytes, standardizing the packet size for OBD2 signals.
The OBD2 adapter cable must be max 5 meters long, limiting signal degradation for reliable OBD2 signal transmission.

OBD2 CAN Identifiers: Directing OBD2 Signals (11-bit, 29-bit)

All OBD2 communication relies on request/response message exchanges for OBD2 signals.

In most cars, 11-bit CAN IDs are used for OBD2 signal communication. The ‘Functional Addressing’ ID is 0x7DF, which broadcasts a request to all OBD2-compatible ECUs, asking if they have data to report on the requested parameter. CAN IDs 0x7E0-0x7E7 are used for ‘Physical Addressing’ requests to specific ECUs, though less commonly used for general OBD2 signal requests.

ECUs respond with 11-bit IDs in the range 0x7E8-0x7EF. The most common response ID is 0x7E8 (ECM, Engine Control Module), followed by 0x7E9 (TCM, Transmission Control Module). These IDs are crucial for routing OBD2 signals correctly.

In some vehicles (vans, light/medium/heavy-duty vehicles), extended 29-bit CAN identifiers may be used for OBD2 signal communication instead of 11-bit IDs.

Here, the ‘Functional Addressing’ CAN ID is 0x18DB33F1.

Responses use CAN IDs ranging from 0x18DAF100 to 0x18DAF1FF (typically 18DAF110 and 18DAF11E). The response ID is sometimes shown in the ‘J1939 PGN’ format, specifically PGN 0xDA00 (55808), which in the J1939-71 standard is marked as ‘Reserved for ISO 15765-2’, again highlighting the standardized nature of OBD2 signals.

OBD2 vs. Proprietary CAN Protocols: Distinguishing Signal Types

It’s important to understand that your car’s ECUs do not rely on OBD2 for their primary functions. Each OEM implements proprietary CAN protocols for internal communication. These protocols are often specific to the vehicle brand, model, and year and carry different types of signals than standardized OBD2 signals. Accessing and interpreting these proprietary signals usually requires reverse engineering.

Connecting a CAN bus data logger to your car’s OBD2 connector might reveal OEM-specific CAN data, typically broadcast at high rates. However, many newer cars use a ‘gateway’ to block access to this OEM CAN data via the OBD2 connector, only allowing standardized OBD2 signals to pass through.

Think of OBD2 as an ‘additional’ higher-layer protocol running alongside the OEM-specific protocol. Both systems transmit signals, but OBD2 signals are standardized for diagnostics, while OEM signals are for vehicle operation.

Bit-rate and ID Validation: Ensuring Correct OBD2 Signal Interpretation

OBD2 can use two bit-rates (250K, 500K) and two CAN ID lengths (11-bit, 29-bit), resulting in 4 potential combinations for OBD2 signal transmission. Modern cars commonly use 500K and 11-bit IDs. External tools should systematically validate these parameters to correctly interpret OBD2 signals.

ISO 15765-4 recommends an initialization sequence to determine the correct combination. This process leverages the fact that OBD2-compliant vehicles must respond to a mandatory OBD2 request (see the OBD2 PID section) and that incorrect bit-rates cause CAN error frames, disrupting OBD2 signal communication.

Newer versions of ISO 15765-4 consider that vehicles may support OBD communication via OBDonUDS rather than OBDonEDS. This article focuses on OBD2/OBDonEDS (OBD on emission diagnostic service as per ISO 15031-5/SAE J1979) versus WWH-OBD/OBDonUDS (OBD on Unified Diagnostic Service as per ISO 14229, ISO 27145-3/SAE J1979-2). These different approaches affect how OBD2 signals are structured and transmitted.

To test for OBDonEDS vs. OBDonUDS, tools may send 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, indicating their protocol for OBD2 signal handling.

OBDonEDS (aka OBD2, SAE OBD, EOBD, or ISO OBD) is used in most non-EV cars today, while WWH-OBD is primarily used in EU trucks/buses. Understanding these protocols is key to correctly interpreting OBD2 signals.

Five Lower-Layer OBD2 Protocols: Historical Context of OBD2 Signals

CAN is now the dominant lower-layer protocol for OBD2 as per ISO 15765. However, older cars (pre-2008) might use other protocols. Knowing these protocols and their pinouts can help diagnose older systems and understand the evolution of OBD2 signal transmission.

The five lower-layer protocols used for OBD2, reflecting different methods of transmitting OBD2 signals:

ISO 15765 (CAN bus): Mandatory in US cars since 2008, now widely used.
ISO14230-4 (KWP2000): Common in 2003+ cars, especially in Asia.
ISO 9141-2: Used in EU, Chrysler & Asian cars in 2000-04.
SAE J1850 (VPW): Mostly in older GM cars.
SAE J1850 (PWM): Mostly in older Ford cars.

Transporting OBD2 Messages via ISO-TP: Handling Complex OBD2 Signals [ISO 15765-2]

All OBD2 data is transmitted on the CAN bus using ISO-TP (ISO 15765-2), a transport protocol. This protocol enables transmission of payloads larger than 8 bytes, necessary for complex OBD2 signals like VIN or DTCs. ISO 15765-2 handles segmentation, flow control, and reassembly of these larger OBD2 signals. For details, see our intro to UDS.

For simpler OBD2 signals that fit within a single CAN frame, ISO 15765-2 specifies ‘Single Frame’ (SF) usage. The first data byte (PCI field) indicates the payload length, leaving 7 bytes for OBD2 communication.

The OBD2 Diagnostic Message: Decoding OBD2 Signals [SAE J1979, ISO 15031-5]

To understand OBD2 on CAN, let’s examine a raw ‘Single Frame’ OBD2 CAN message. An OBD2 message comprises an identifier, data length (PCI field), and data. The data section is further structured into Mode, Parameter ID (PID), and data bytes, all contributing to the composition of OBD2 signals.

Example: OBD2 Request/Response – Vehicle Speed Signal

Consider an example request/response for ‘Vehicle Speed’ to illustrate how OBD2 signals are exchanged.

An external tool sends a request message to the car with CAN ID 0x7DF and 2 payload bytes: Mode 0x01 and PID 0x0D. The car responds with CAN ID 0x7E8 and 3 payload bytes, including the Vehicle Speed value in the 4th byte, 0x32 (50 in decimal). These bytes together form the OBD2 signal representing vehicle speed.

Looking up the decoding rules for OBD2 PID 0x0D, we find that 0x32 translates to a physical value of 50 km/h. This decoding process is crucial for interpreting OBD2 signals.

Next, we’ll explore OBD2 modes and PIDs in more detail to understand the full range of OBD2 signals available.

The 10 OBD2 Services (Modes): Categories of OBD2 Signals

There are 10 standardized OBD2 diagnostic services or modes, each representing a category of OBD2 signals. Mode 0x01 provides real-time data, while others are used for Diagnostic Trouble Codes (DTCs) or freeze frame data.

Vehicles are not required to support all 10 OBD2 modes and may also support OEM-specific modes beyond these standards. The supported modes define the range of OBD2 signals a vehicle can provide.

In OBD2 messages, the mode is indicated in the 2nd byte. In requests, the mode is included directly (e.g., 0x01), while in responses, 0x40 is added to the mode value (e.g., resulting in 0x41). This modification helps distinguish request and response OBD2 signals.

OBD2 Parameter IDs (PIDs): Specific OBD2 Signals

Each OBD2 mode contains Parameter IDs (PIDs), which are unique identifiers for specific OBD2 signals.

For example, mode 0x01 contains ~200 standardized PIDs representing real-time data like speed, RPM, and fuel level. However, vehicles typically support only a subset of these PIDs, meaning the available OBD2 signals vary by vehicle.

One PID is particularly important:

If an emissions-related ECU supports any OBD2 services, it must support mode 0x01 PID 0x00. Responding to PID 0x00, the ECU indicates whether it supports PIDs 0x01-0x20. This makes PID 0x00 a fundamental ‘OBD2 compatibility test’ and a starting point for exploring available OBD2 signals. PIDs 0x20, 0x40, …, 0xC0 can be used to determine support for the remaining mode 0x01 PIDs.

Tip: OBD2 PID Overview Tool – Your Guide to OBD2 Signals

SAE J1979 and ISO 15031-5 appendices detail scaling information for standard OBD2 PIDs, enabling you to decode data into physical values. Our CAN bus intro explains this decoding process in detail, which is essential for working with OBD2 signals.

For quick lookup of mode 0x01 PIDs, use our OBD2 PID overview tool. It helps construct OBD2 request frames and dynamically decode OBD2 responses, simplifying the process of accessing and interpreting OBD2 signals.

OBD2 PID overview tool

Logging and Decoding OBD2 Data: Practical Steps to Capture OBD2 Signals

This section provides a practical guide on logging OBD2 data using the CANedge CAN bus data logger. This will demonstrate how to capture and work with real OBD2 signals.

The CANedge allows configuration of custom CAN frames for transmission, making it suitable for OBD2 logging.

Connect the CANedge to your vehicle using our OBD2-DB9 adapter cable to start logging OBD2 signals.

Validating bit-rate is crucial for correct OBD2 signal capture.

Reviewing supported PIDs in asammdf helps understand the range of OBD2 signals.

#1: Test Bit-rate, IDs & Supported PIDs – Initial OBD2 Signal Discovery

ISO 15765-4 outlines how to determine the bit-rate and IDs used by a vehicle. The CANedge can be used to perform these tests:

Send a CAN frame at 500K and check for success (if unsuccessful, try 250K). This step ensures correct bit-rate for OBD2 signal communication.
Use the identified bit-rate for subsequent communication to ensure reliable OBD2 signal exchange.
Send multiple ‘Supported PIDs’ requests and review the responses to discover the range of available OBD2 signals.
Response IDs indicate 11-bit vs. 29-bit CAN ID usage, important for addressing OBD2 signals.
Response data reveals supported PIDs, defining the specific OBD2 signals available from the vehicle.

Plug & play configurations for these tests are available, simplifying the initial setup for OBD2 signal logging.

Most 2008+ non-EV cars support 40-80 PIDs via 500K bit-rate, 11-bit CAN IDs, and the OBD2/OBDonEDS protocol, providing a rich set of OBD2 signals.

As seen in the asammdf GUI screenshot, multiple responses to a single OBD request are common due to the 0x7DF request ID polling all ECUs. All OBD2/OBDonEDS-compliant ECUs must support service 0x01 PID 0x00, leading to multiple responses, especially for this PID. Subsequent ‘Supported PIDs’ requests receive fewer responses as fewer ECUs support those specific OBD2 signals. The ECM ECU (0x7E8) often supports all PIDs supported by other ECUs, reducing busload by directing requests specifically to this ECU using ‘Physical Addressing’ CAN ID 0x7E0 for subsequent OBD2 signal requests.

#2: Configure OBD2 PID Requests – Selecting Specific OBD2 Signals

After identifying supported PIDs, configure your transmit list with PIDs of interest. This allows you to selectively log specific OBD2 signals.

Consider these points when configuring PID requests:

CAN IDs: Use ‘Physical Addressing’ request IDs (e.g., 0x7E0) to avoid multiple responses and focus on specific OBD2 signals from target ECUs.
Spacing: Add 300-500 ms between OBD2 requests to prevent overwhelming ECUs and ensure reliable OBD2 signal responses.
Battery drain: Use triggers to stop transmissions when the vehicle is inactive to avoid battery drain and unnecessary ECU activity related to OBD2 signal requests.
Filters: Filter to record only OBD2 responses if OEM-specific CAN data is also present, focusing your logs on relevant OBD2 signals.

With these configurations, the device is ready to log raw OBD2 data, capturing the desired OBD2 signals.

Example CANedge OBD2 PID request list for selective OBD2 signal logging.

asammdf enables DBC decoding and visualization of logged OBD2 signals.

#3: DBC Decode Raw OBD2 Data – Interpreting OBD2 Signals

To analyze and visualize logged data, decode raw OBD2 data into ‘physical values’ (km/h, °C). This step is crucial for making sense of the captured OBD2 signals.

Decoding information is in ISO 15031-5/SAE J1979 and online resources like Wikipedia. We offer a free OBD2 DBC file for easy DBC decoding in CAN bus software tools, simplifying the interpretation of OBD2 signals.

Decoding OBD2 data is more complex than regular CAN signals. Different OBD2 PIDs use the same CAN ID (e.g., 0x7E8), meaning the CAN ID alone isn’t enough to identify signals within the payload.

You must use the CAN ID, OBD2 mode, and OBD2 PID to uniquely identify signals. This ‘extended multiplexing’ is supported in DBC files, allowing for accurate interpretation of OBD2 signals.

CANedge: Your OBD2 Data Logger – Dedicated Tool for OBD2 Signals

The CANedge easily records OBD2 data to an 8-32 GB SD card. Connect to a car/truck to start logging and decode data with free software/APIs and our OBD2 DBC. It’s a dedicated tool for capturing and utilizing OBD2 signals.

OBD2 logger intro
CANedge

OBD2 Multi-Frame Examples: Handling Complex OBD2 Signals [ISO-TP]

All OBD2 data uses ISO-TP (ISO 15765-2). Most examples so far are single-frame communication. This section provides multi-frame communication examples, showing how more complex OBD2 signals are handled.

Multi-frame OBD2 communication requires flow control frames. A static flow control frame can be transmitted ~50 ms after the initial request frame, as in the CANedge configuration example. This ensures proper handling of multi-frame OBD2 signals.

Multi-frame OBD2 responses need CAN software/API tools supporting ISO-TP, like CANedge MF4 decoders, to correctly reassemble and interpret complex OBD2 signals.

Example 1: OBD2 Vehicle Identification Number (VIN) – A Multi-Frame OBD2 Signal

The Vehicle Identification Number (VIN) is relevant for telematics and diagnostics. Request the VIN using OBD2 mode 0x09 and PID 0x02. This is an example of a multi-frame OBD2 signal request.

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

The vehicle responds with a First Frame containing PCI, length (0x014 = 20 bytes), mode (0x49), and PID (0x02). Byte 0x01 follows the PID, indicating Number Of Data Items (NODI), in this case 1. The remaining 17 bytes are the VIN, convertible from HEX to ASC. This multi-frame response carries the complete OBD2 signal for VIN.

Example 2: OBD2 Multi-PID Request (6x) – Efficiently Requesting Multiple OBD2 Signals

External tools can request up to 6 mode 0x01 OBD2 PIDs in one request frame for efficient data collection. The ECU responds with data for supported PIDs, potentially across multiple frames. This method allows for high-frequency OBD2 signal collection.

However, signal encoding becomes specific to the request method, making generic OBD2 DBC files less useful. This method is not generally recommended.

The multi-frame response is similar to the VIN example but includes requested PIDs and their data. PIDs are often ordered as requested, common but not mandatory per ISO 15031-5. This complex response structure carries multiple OBD2 signals in a single exchange.

Decoding this response with generic DBC files is difficult. It involves extended multiplexing with payload position-specific PIDs, making it hard to generalize DBC files across vehicles. Handling multiple such requests further complicates DBC manipulation. Custom scripts and recording transmit messages can help, but are complex to scale. This method, while efficient, presents challenges in reliably interpreting OBD2 signals.

Example 3: OBD2 Diagnostic Trouble Codes (DTCs) – Decoding Error-Indicating OBD2 Signals

Use OBD2 mode 0x03 (‘Show stored Diagnostic Trouble Codes’) to request emissions-related DTCs. No PID is in the request. The ECU responds with the number of stored DTCs, each taking 2 bytes. Multi-frame responses are needed for more than 2 DTCs, demonstrating how error-related OBD2 signals are structured.

The 2-byte DTC value is split as per ISO 15031-5/ISO 15031-6. The first 2 bits define the ‘category’, and the remaining 14 bits form a 4-digit hexadecimal code. Decoded DTC values can be looked up using OBD2 DTC lookup tools like repairpal.com. These DTCs are crucial OBD2 signals for diagnostics.

The example below shows a request to an ECU with 6 DTCs stored, resulting in a multi-frame response carrying all error-indicating OBD2 signals.

OBD2 Data Logging – Use Case Examples: Applications of OBD2 Signals

OBD2 data from cars and light trucks has diverse applications, leveraging the rich information contained in OBD2 signals:

Logging Data from Cars – Utilizing OBD2 Signals for Vehicle Insights

OBD2 data helps reduce fuel costs, improve driving habits, test prototype parts, and inform insurance models. By analyzing OBD2 signals, valuable insights can be derived for various applications.

obd2 logger

Real-time Car Diagnostics – Leveraging OBD2 Signals for Immediate Vehicle Health Assessment

OBD2 interfaces stream human-readable OBD2 data in real-time for vehicle diagnostics. Interpreting OBD2 signals in real-time allows for immediate issue detection and troubleshooting.

obd2 streaming

Predictive Maintenance – Using OBD2 Signals for Proactive Vehicle Care

IoT OBD2 loggers monitor cars and light trucks in the cloud to predict and prevent breakdowns. Analyzing trends in OBD2 signals enables proactive maintenance and reduces downtime.

predictive maintenance

Vehicle Blackbox Logger – Recording OBD2 Signals for Event Analysis

An OBD2 logger serves as a ‘blackbox’ for vehicles or equipment, providing data for disputes or diagnostics. Recorded OBD2 signals offer crucial evidence and insights in case of incidents.

can bus blackbox

Do you have an OBD2 data logging use case? Contact us for free expert consultation!

For more introductions, see our guides section or download the ‘Ultimate Guide’ PDF.

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