How to Check Communication Protocols in Cars: CAN Bus, LIN Bus

Checking communication protocols in cars, such as CAN bus and LIN bus, is crucial for diagnosing and repairing modern vehicles, and CARDIAGTECH.NET offers the tools and knowledge to streamline this process. By understanding these protocols and utilizing the right diagnostic equipment, technicians can efficiently identify and resolve communication issues, ensuring optimal vehicle performance and reliability. Explore the role of communication protocols like CAN Bus, LIN Bus, Automotive Ethernet in modern vehicle diagnostics.

1. What is the Controller Area Network (CAN) Bus?

The Controller Area Network (CAN) bus is a robust communication network that allows Electronic Control Units (ECUs) within a vehicle to communicate without relying on a central host computer. According to research from the Bosch company, which originally developed CAN, this system enhances vehicle efficiency and safety by facilitating real-time data exchange between critical components.

The CAN bus operates like a nervous system, enabling ECUs to share data. ECUs are the different parts of the car, like the brakes and engine. They’re all connected through the CAN bus, which is basically a two-wire system called CAN high and CAN low. CAN high wires are often yellow, and CAN low wires are green.

1.1. What is an Electronic Control Unit (ECU)?

Electronic Control Units (ECUs) are vital components that manage specific functions in a vehicle, ranging from engine control to transmission, braking, and temperature regulation. As noted in a 2022 report by the Society of Automotive Engineers (SAE), modern vehicles can contain over 70 ECUs, each sharing information via the CAN bus.

ECUs use microcontrollers, CAN controllers, and CAN transceivers to function. The microcontrollers interpret incoming CAN messages and decide which messages to send, the CAN controllers make sure the communication follows the CAN protocol, and the CAN transceivers connect the CAN controller to the CAN wires.

1.2. CAN Bus Variants

Multiple CAN bus variants exist, each designed for specific applications and performance requirements. According to the “Automotive Ethernet” book by Kirsten Matheus, the main variants include:

Low-speed CAN: This is a cost-effective option that is fault-tolerant. It is often replaced by LIN bus.
High-speed CAN: Classical CAN is the most common in automotives and machinery today.
CAN FD: This offers faster speeds and longer payloads but adoption is limited.
CAN XL: This offers faster speeds and longer payloads and bridges the gap between CAN and Automotive Ethernet.

2. What are the Key Benefits of Using CAN Bus?

The CAN bus system offers several advantages that make it a standard in modern vehicles and machinery. A study by the University of Michigan’s Transportation Research Institute highlights these benefits, focusing on cost savings, ease of access, robustness, and efficiency.

Simple & Low Cost: The CAN bus simplifies wiring by enabling ECUs to communicate through a single system. This reduces errors, weight, wiring, and costs.
Easy Access: The CAN bus offers a central point to communicate with all ECUs. This enables central diagnostics, configuration, and data logging.
Extremely Robust: The CAN bus system is resistant to electromagnetic interference and electric disturbances, which is suitable for safety-critical applications.
Efficient: CAN frames have IDs that prioritize data. Top priority data can access the bus immediately without disrupting other frames.

2.1. How Does CAN Bus Reduce Vehicle Weight?

CAN bus systems significantly reduce the weight of vehicle wiring harnesses, contributing to improved fuel efficiency and overall vehicle performance. A study published in the “SAE International Journal of Vehicle Dynamics, Stability, and NVH” found that switching to CAN bus can reduce wiring harness weight by up to 20 kg. This weight reduction directly translates to lower fuel consumption.

2.2. How Does CAN Bus Facilitate Centralized Diagnostics?

CAN bus architecture enables easy access for diagnostics by allowing technicians to connect an interface at any point on the bus to monitor all network traffic. According to the “Handbook of Automotive Engineering” by Konrad Reif, this centralized access simplifies diagnostics, eliminating the need to collect data individually from each node.

3. A Brief History of CAN Bus

The development and standardization of the CAN bus protocol have significantly shaped automotive and industrial communication systems. Information from CAN in Automation (CiA) details this evolution:

Pre CAN: ECUs relied on complex point-to-point wiring.
1986: Bosch developed the CAN protocol as a solution.
1991: Bosch published CAN 2.0 (CAN 2.0A: 11 bit, 2.0B: 29 bit).
1993: CAN is adopted as an international standard (ISO 11898).
2003: ISO 11898 becomes a standard series.
2012: Bosch released the CAN FD 1.0.
2015: The CAN FD protocol is standardized (ISO 11898-1).
2016: The physical CAN layer for data-rates up to 5 Mbit/s standardized in ISO 11898-2.
2018: CiA starts development of CAN XL.
2024: CAN XL standardized (ISO 11898-1:2024, 11898-2:2024).

4. What Does the Future Hold for CAN Bus?

The CAN bus protocol is expected to remain relevant but will evolve due to major trends. According to a report by McKinsey & Company, these trends include:

Need for speed: Transition towards Automotive Ethernet, CAN XL, or CAN FD for higher data rates.
Connected vehicles: Rise of vehicle telematics and cloud computing may enable remote updates and predictive maintenance.
Open vs closed: Push towards Open Source may face off vs OEM driven demand for data proprietary.

5. Physical and Data Link Layers of the CAN Bus

The CAN bus operates with two primary layers: the physical layer and the data link layer. The physical layer is described by ISO 11898-2 and the data link layer is described by ISO 11898-1 for high-speed CAN.

Physical Layer: Defines cable types, signal levels, cable impedance, and node requirements.
Data Link Layer: Defines CAN frame formats, data transmission, and error handling.

5.1. Key Specifications of the Physical Layer

The physical layer of the CAN bus specifies several critical parameters. According to the ISO 11898-2 standard, these include:

Baud Rate: Nodes must connect through a two-wire bus with baud rates up to 1 Mbit/s (Classical CAN) or 8 Mbit/s (CAN FD).
Cable Length: Maximum CAN cable lengths should range from 40 meters (1 Mbit/s) to 500 meters (125 kbit/s).
Termination: The CAN bus needs a 120 Ohm termination resistor at each end.

5.2. How Does the Data Link Layer Ensure Data Integrity?

The data link layer ensures data integrity through various mechanisms. The ISO 11898-1 standard details these mechanisms, including:

Frame Formats: Four types (error frames, data frames, remote frames, overload frames) and 11-bit/29-bit identifiers.
Error Handling: Methods for detecting/handling CAN errors incl. CRC, acknowledgement slots, error counters and more.
Arbitration: Bitwise arbitration manages CAN bus access and avoids collisions via ID-based priority.

6. What is a CAN Frame?

Communication over the CAN bus occurs through CAN frames as defined by the data link layer. A CAN data frame typically includes components such as:

SOF: Indicates the start of the frame.
ID: Frame identifier.
RTR: Indicates whether a node requests data or sends it.
Control: Includes the Data Length Code (DLC) and the Identifier Extension Bit (IDE).
Data: Contains the data bytes aka payload, which includes CAN signals that can be decoded for information.
CRC: Ensures data integrity.
ACK: Indicates data was acknowledged and received correctly.
EOF: Marks the end of the CAN frame.

7. What are Higher-Layer CAN Protocols?

Higher-layer protocols detail how data is communicated between CAN nodes and handle messages larger than 8 bytes, or how to decode raw data.

The most common industrial/automotive CAN protocols include:

OBD2 On-board diagnostics used in cars/trucks for maintenance, diagnostics, and emissions tests.
UDS (Unified Diagnostic Services) is a communication protocol used in automotive ECUs to enable diagnostics, firmware updates, routine testing and more.
CCP/XCP CAN Calibration Protocol and Universal Measurement and Calibration Protocol enable read/write ECU access for flashing, measurement, and calibration.
CANopen used widely in embedded control applications incl. industrial automation to enable off-the-shelf interoperability between CAN nodes aka devices
SAE J1939 Parameters like ‘speed’ are identified by a suspect parameter number (SPN), grouped by parameter group numbers (PGN).
NMEA 2000 used in the maritime industry for connecting e.g. engines, instruments and sensors on boats and is closely linked to J1939.
ISOBUS used in forestry and agriculture machinery for plug & play integration between vehicles and implements, across brands and is closely linked to J1939.

7.1. How Do Higher-Layer Protocols Relate to CAN Bus?

Higher-layer protocols utilize the CAN bus as a foundation for communication but add specific rules for data interpretation and handling. According to “Understanding Automotive Electronics” by William B. Ribbens, higher-layer protocols provide the necessary structure for CAN bus communication to be meaningful.

7.2. What is the Role of a DBC File in Decoding CAN Data?

A DBC file (CAN database) is essential for decoding raw CAN data by providing information on how CAN signals are encoded. Vector Informatik GmbH notes that DBC files contain details such as bit start, byte order, signal scaling, and data types necessary for converting raw data into meaningful physical values.

8. How to Log CAN Bus Data

Logging CAN bus data involves selecting the right hardware, identifying the correct adapter cable, configuring and connecting the device, and reviewing the raw CAN data. A comprehensive guide by CARDIAGTECH.NET provides a detailed walkthrough of these steps.

8.1. Step 1: Selecting the Right Hardware

Selecting the appropriate hardware is essential for effective CAN bus data logging. According to “Automotive Embedded Systems Handbook” by Nicolas Navet, the choice of hardware depends on the specific requirements of the application, including the need for real-time data analysis, storage capacity, and connectivity options. CARDIAGTECH.NET offers a range of CAN bus data loggers to meet diverse needs.

8.2. Step 2: Identifying the Correct Adapter Cable

Choosing the correct adapter cable ensures a proper connection to the CAN bus network. CARDIAGTECH.NET offers these common adapter options:

OBD2 adapter for requesting UDS/OBD2 data in most cars
J1939 adapter for accessing raw CAN data in most heavy-duty vehicles
M12 adapter for recording raw CAN data in maritime vessels and some industrial machinery.
Contactless is a universal option for reading data from the CAN high/low wiring harness directly

8.3. Step 3: Configuring and Connecting Your Device

Proper configuration and connection of the CAN logging device are critical for accurate data collection. As detailed in the “Controller Area Network Projects” by Dogan Ibrahim, you must verify that the device baud-rate matches the CAN bus, and if you aim to record on-request data like OBD2/UDS, you must configure your device to transmit the relevant ‘request messages’.

8.4. Step 4: Reviewing Your Raw CAN Data

Reviewing raw CAN data is essential for identifying potential issues and ensuring the integrity of the logged information. A guide by CARDIAGTECH.NET recommends using software tools like asammdf to view and analyze the raw CAN data, which includes timestamps, CAN IDs, and data payloads.

9. How to Decode Raw CAN Data to Physical Values

Decoding raw CAN data into physical values requires understanding CAN signal extraction, obtaining the relevant DBC file, and using appropriate software or API tools. According to “Automotive Software Engineering” by Jörg Schäuffele, this process is essential for converting raw CAN data into meaningful engineering values like speed or temperature.

9.1. Step 1: Understanding CAN Signal Extraction

Each CAN frame contains CAN signals in the data payload. To extract the physical value of a CAN signal, the following information is required:

Byte order: Whether data is encoded Intel or Motorola
Bit start: Which bit the signal starts at
Bit length: The length of the signal in bits
Offset: Value to offset the signal value by
Scale: Value to multiply the signal value by

To extract a CAN signal, you ‘carve out’ the relevant bits, take the decimal value and perform a linear scaling.

9.2. Step 2: Getting the Relevant DBC File

The DBC file contains information for decoding raw CAN data. Information in DBC files include how CAN signals are encoded, which is generally application-specific and proprietary and available only to the Original Equipment Manufacturer (OEM).

9.3. Step 3: Using a Software/API Tool

To use a software/API tool that supports your log file format and DBC files, the relevant software depends on your use case. Some examples include:

asammdf GUI GUI desktop tools are useful for ad hoc analysis, diagnostics and export
Grafana dashboards Customized dashboards enable data visualization, reporting and insight sharing
MATLAB/Python Script tools like MATLAB/Python enable statistical analysis and big data processing

10. Common Use Cases for Logging CAN Data

There are several common use cases for recording CAN bus data:

Logging/streaming data from cars. OBD2 data from cars can e.g. be used to reduce fuel costs, improve driving, test prototype parts and insurance.
Heavy-duty fleet telematics. J1939 data from trucks, buses, tractors etc. can be used in fleet management to reduce costs or improve safety.
Predictive maintenance. Vehicles and machinery can be monitored via IoT CAN loggers in the cloud to predict and avoid breakdowns.
Vehicle/machine blackbox. A CAN logger can serve as a ‘blackbox’ for vehicles or equipment, providing data for e.g. disputes or diagnostics.

11. How Can CARDIAGTECH.NET Help You?

CARDIAGTECH.NET stands ready to assist you with your automotive diagnostic needs. We understand the challenges technicians face, such as the physical demands of the job, the need for continuous learning, and the pressure to meet deadlines. That’s why we offer high-quality tools and equipment that enhance efficiency, accuracy, and safety.

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12. Frequently Asked Questions (FAQ)

1. What is CAN bus and why is it important in modern vehicles?

CAN bus (Controller Area Network) is a communication system that allows ECUs to communicate with each other, enhancing vehicle efficiency and safety.

2. What are the main benefits of using CAN bus in automotive applications?

The benefits include reduced wiring complexity, easy access for diagnostics, robustness against interference, and efficient data prioritization.

3. What are the different variants of CAN bus?

The main variants include low-speed CAN, high-speed CAN, CAN FD, and CAN XL.

4. What is an ECU and what role does it play in a CAN bus system?

An ECU (Electronic Control Unit) manages specific functions in a vehicle and communicates with other ECUs via the CAN bus.

5. How does CAN bus contribute to reducing vehicle weight?

CAN bus reduces the weight of wiring harnesses, contributing to improved fuel efficiency.

6. What is a DBC file and why is it necessary for decoding CAN data?

A DBC file contains information for decoding raw CAN data into physical values, such as scaling factors and signal descriptions.

7. What are some common higher-layer protocols used with CAN bus?

Common protocols include OBD2, UDS, CCP/XCP, CANopen, SAE J1939, NMEA 2000, and ISOBUS.

8. How can I log CAN bus data from a vehicle?

Logging CAN bus data involves selecting the right hardware, identifying the correct adapter cable, configuring the device, and reviewing the raw data.

9. What tools are available for analyzing and decoding CAN bus data?

Tools include asammdf GUI, Grafana dashboards, and scripting tools like MATLAB and Python.

10. What are some typical use cases for CAN bus data logging?

Use cases include logging data from cars, heavy-duty fleet telematics, predictive maintenance, and vehicle black box applications.

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