Unified Diagnostic Services(UDS)

Understanding UDS (Unified Diagnostic Services) in Automotive

Unified Diagnostic Services (UDS) is a communication protocol used in automotive applications, mainly for diagnostics. It is part of the ISO 14229 standard and is implemented over the Controller Area Network (CAN) and other automotive networks. UDS provides a standard set of services for vehicle diagnostics, allowing testing and diagnostics of vehicle systems and components.

Key Features of UDS

• Standardized Diagnostic Requests: UDS offers a set of standardized diagnostic requests that automotive systems understand, facilitating consistent and reliable communications.

• Wide Range of Services: Includes services for diagnostic trouble code management, data reading, data erasure, communication control, data logging, and more.

• Enhanced Vehicle Diagnostics: UDS enables comprehensive diagnostics, helping in pinpointing issues, updating software, and configuring system parameters.

Flow Diagram of UDS Request & Response between Client and Server

UDS plays a crucial role in vehicle maintenance and repair processes, allowing technicians to efficiently diagnose and resolve issues.

UDS Request & Response Message Format

UDS Request

For Example: cansend can0 123#0211010000000000

Here:

Protocol Control Info: 0x02

Negative Response ID: 0x11(ECU Reset)

Sub Function: 0x01(Hard Reset)

Padding is optional: 0000000000

Positive Response

Negative Response

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Detailed Overview of UDS Services

Unified Diagnostic Services (UDS) incorporate a variety of services that facilitate advanced diagnostics and communications in automotive systems. Below is a detailed exploration of these essential services:

Service ID	Response ID	Service Name	Subfunction/Information
0x10	0x50	Diagnostic Session Control	01 Default Session 02 Programming 03 Extended 04 Safety
0x11	0x51	ECU Reset	01 Hard Reset 02 Key Off 03 Soft Reset
0x27	0x67	Security Access	01 Seed Request 02 Send Key
0x28	0x68	Communication Control	00 Enable RX & TX 01 Enable RX & Disable TX 02 Disable RX & Enable TX 03 Disable RX & TX
0x29	0x69	Authentication	Used in SecOC
0x3E	0x7E	Tester Present	To signal the ECU that the tester is still present
0x83	0xC3	Access Timing Params	Read/Write the default timing of comm. link
0x84	0xC4	Secure Data Transmission	Send encrypted data according to ISO 15764
0x85	0xC5	Control DTC Settings	01 DTC Activate 02 DTC Deactivate
0x86	0xC6	Response on Event	Configure ECU to send response on a defined event
0x87	0xC7	Link Control	Set the Baud Rate
0x22	0x62	Read Data by Identifier	Read Data from the ECU
0x23	0x63	Read Memory by Identifier	Read Data from Memory
0x24	0x64	Read Scaling Data by Identifier	Read the Scaling Info of a Record
0x2A	0x6A	Read Data by Identifier Periodic	Request the Periodic Transmission of Data Record Values
0x2C	0x6C	Dynamically Define Data Identifier	Fix for a Device Specified Data Identifier(DID) Pool to Configure Another Data Identifier
0x2E	0x6E	Write Data by Identifier	Write Value to DIDs
0x3D	0x7D	Write Memory by Identifier	Write Information to the ECU's Memory
0x14`	0x54	Clear Diagnostic Info	Delete Stored DTCs
0x19	0x59	Read DTC Information	Read Stored DTCs Info
0x2F	0x6F	I/O Control by Identifier	Control over the ECU's Analog or Digital I/O
0x31	0x71	Routine Control	01 Start Routine 02 Stop Routine 03 Request for the Results
0x34	0x74	Request Download	Request to Add SW/Data into the ECU
0x35	0x75	Request Upload	Request or Read SW/Data from the ECU
0x36	0x76	Transfer Data	Actual Data Transfer of 0x74 & 0x75
0x37	0x78	Request File Transfer	Initiate a File Download from the Tester to ECU or Upload from ECU to the Tester
	0x7F	Negative Response	A Negative Response Code(NRC) Will Be Included With It

List of Negative Response Code

UDS NRC	Description
0x10	General Reject
0x11	Service Not Supported
0x12	Sub Function Not Supported
0x13	Invalid Message Format/Length
0x14	Response Too Long
0x21	Busy- Repeat Request
0x22	Conditions Not Correct
0x24	Request Sequence Error
0x25	No Response From Subnet Component
0x26	Failure Prevents Execution of Request Action
0x31	Request Out of Range
0x33	Security Access Denied
0x35	Invalid Key
0x36	Exceeded Number of Attempts
0x37	Required Time Delay has not Expired
0x70	Upload/Download Not Accepted
0x71	Transfer Data Suspended
0x73	Wrong Block Sequence Counter
0x78	Request Received - Response Pending
0x7E	Sub Function Not Supported in Active Session
0x7F	Service Not Supported in Active Session
0x81/0x82	RPM is too High/Low
0x83/0x84	Engine is Running/Not Running
0x85	Engine Run Time is too Low
0x86/0x87	Temperature too High/Low
0x88/0x89	Speed too High/Low
0x8A/0x8B	Throttle Pedal too High/Low
0x8C/0x8D	Transmission Range Not in Neutral/Gear
0x8F	Brake Switches Not Closed
0x90	Shift Lever Not in Park
0x91	Torque Converter Clutch Locked
0x92/0x93	Voltage too High/Low
0xF0/0xFE	Manufacturer Specific Conditions Not Correct