What Is Unified Diagnostic Services (UDS) and How Does It Work?

TL;DR

Unified Diagnostic Services (UDS) is a standardized communication protocol used in automotive ECUs for diagnostics, firmware updates, and routine testing. It enables client-server communication between tester tools and vehicle ECUs, allowing for tasks like reading diagnostic trouble codes and extracting parameter data across various bus systems.

Transcript

Need a simple intro to UDS  (Unified Diagnostic Services)?  In this practical tutorial, we introduce the  UDS basics with focus on UDS on CAN bus and   Diagnostics over CAN (DoCAN). We also introduce  the ISO-TP protocol and explain the difference   between UDS, OBD2, WWH-OBD and OBDonUDS. Finally, we explain how to request,   record and decode UDS... Read More

Key Insights

• 🚗 Unified Diagnostic Services (UDS) is a communication protocol used in automotive ECUs for diagnostics, firmware updates, and more. It is standardized across manufacturers and standards. UDS is used by all tier 1 OEMs today.
• 🔌 UDS communication is performed in a client-server relationship, with the client being a tester-tool and the server being a vehicle ECU. This enables various use cases such as reading and clearing diagnostic trouble codes, extracting parameter data, initiating diagnostic sessions, and modifying ECU behavior.
• 🌐 UDS is based on the ISO 14229 protocol and can be used on various bus systems like CAN, FlexRay, IP, K-line, and LIN.
• 📟 The UDS message structure includes fields like Protocol Control Information (PCI), UDS Service ID (SID), UDS Sub Function Byte, and UDS Request Data Parameters. These fields are used to configure and control the UDS communication.
• 🔍 ISO-TP (ISO 15765-2) is a transport protocol used in CAN-based vehicle networks to handle larger payloads for diagnostics. It enables segmentation, flow control, and reassembly of CAN data payloads up to 4095 bytes.
• 🔢 UDS messages can be single-frame or multi-frame. Single-frame requests and responses are used when the payload can be contained in a 7-byte frame. Multi-frame requests and responses are used when the payload exceeds 7 bytes and require segmentation and reassembly.
• 🚛 UDS is used in various vehicle diagnostic protocols such as OBD2, World-Wide Harmonized OBD (WWH-OBD), and OBDonUDS. WWH-OBD is a global standard based on UDS, while OBDonUDS is a next-generation OBD2 protocol for US vehicles based on UDS.
• 📊 UDS data can be logged using CANbus data loggers like the CANedge. It can be configured to send UDS requests, record UDS responses, and decode the data using CAN databases (DBC files) or Python API for further analysis.

Questions & Answers

Q: What is the purpose of the UDS protocol in automotive ECUs?

The UDS protocol enables diagnostics, firmware updates, routine testing, and other communication between tester-tools and vehicle ECUs in a standardized manner across manufacturers and standards.

Q: How does UDS communication work between a client and a server?

In UDS communication, the client, such as a tester-tool, sends UDS requests to the server, which is a vehicle ECU. If the targeted ECU supports UDS services, it will respond accordingly.

Q: What are some use cases enabled by UDS communication?

UDS communication allows for reading and clearing diagnostic trouble codes, extracting parameter data values such as temperatures and state of charge, initiating diagnostic sessions, and modifying ECU behavior through resets, firmware flashing, and settings modification.

Q: How does UDS differ from other diagnostic systems like OBD2, WWH-OBD, and OBDonUDS?

UDS is a more comprehensive and feature-rich diagnostic system, used in ECUs for richer diagnostics data and functionality beyond the limits of OBD2. WWH-OBD and OBDonUDS are newer versions of OBD2 based on UDS that provide enhanced emissions-related diagnostics.

Q: How can UDS messages be logged and decoded?

UDS messages can be logged by configuring devices like the CANedge CAN bus data logger to send UDS request frames and record the corresponding responses. The logged UDS messages can then be decoded using tools like Python API or CAN databases (DBC files).

Q: How does the ISO-TP protocol enable communication of large payloads in CAN-based vehicle diagnostics?

The ISO-TP standard defines a transport protocol and network layer services for CAN-based vehicle networks, allowing communication of payloads up to 4095 bytes through segmentation, flow control, and reassembly of CAN frames.

Q: Can UDS be used to request and extract the Vehicle Identification Number (VIN) from a vehicle?

Yes, UDS can be used to request the VIN from a vehicle by sending UDS frames with the appropriate service identifier and data identifier. The VIN can be extracted from the response frames and converted from HEX to ASCII.

Q: What are some practical examples of using UDS data, such as in telematics or predictive maintenance?

Practical examples of using UDS data include requesting sensor parameters from prototype vehicles for telematics purposes, combining UDS data with GNSS/IMU data for analysis, and collecting diagnostic trouble codes for training predictive maintenance models in fleets of vehicles.

Summary & Key Takeaways

• UDS is a standardized communication protocol used in automotive ECUs for diagnostics, firmware updates, and routine testing.

• UDS communication is performed in a client-server relationship, with the client being a tester-tool and the server being a vehicle ECU.

• UDS enables various use cases such as reading/clearing diagnostic trouble codes, extracting parameter data values, and modifying ECU behavior.