UDS Service 0x2C – How to Use Dynamically Define Data Identifier in ECUs

Hello, fellow automotive diagnostics learners! In this blog post, Dynamically Define Data Identifier (0x2C) in UDS. I’ll introduce you to one of the key services in the UDS (Un

ified Diagnostic Services) protocol Service 0x2C, also known as Dynamically Define Data Identifier. This service allows you to group multiple pieces of data under a single custom identifier, making data access more efficient. It’s especially useful in ECU development and testing, where flexibility and speed matter. In this post, we’ll explore what this service does, how it works, its practical use cases, and the message structure involved. We’ll also go through examples to help you understand it clearly. By the end, you’ll be well-equipped to implement or analyze UDS 0x2C in real-world automotive systems. Let’s dive in!

Introduction to Dynamically Define Data Identifier (0x2C) Service in UDS Protocol

In the world of automotive diagnostics, flexibility and efficiency are crucial. The Dynamically Define Data Identifier (DDDI) service, represented by Service ID 0x2C in the UDS protocol, plays a key role in enhancing data handling. This service allows users to create custom data identifiers by combining multiple signals or data elements into one, making access and analysis much more streamlined. It’s especially useful during testing and validation phases, where real-time data grouping is essential. With DDDI, engineers can define exactly what data they want to monitor without altering the ECU software. In this section, we’ll explore what the 0x2C service does, why it’s important, and where it’s typically used in automotive systems. Let’s take a closer look at how it works.

What is Dynamically Define Data Identifier (0x2C) Service in UDS Protocol?

The Dynamically Define Data Identifier (DDDI) is a powerful service in the Unified Diagnostic Services (UDS) protocol, identified by Service ID 0x2C. It allows a diagnostic tester (like a scan tool or testing software) to dynamically create new Data Identifiers (DIDs) by grouping multiple existing DIDs or memory addresses under a single custom-defined identifier. This newly defined identifier can then be used with other services such as ReadDataByIdentifier (0x22) to retrieve grouped data in a single request.

The main advantage of the 0x2C service is efficiency and flexibility especially useful during testing and development phases. Instead of repeatedly requesting individual data elements, engineers can define and read a bundle of related data in one go. This also avoids the need for static reconfiguration of ECU software. Service 0x2C is typically not enabled in production ECUs, due to security concerns, but is commonly used in development and validation environments to simplify data monitoring.

Why do we need Dynamically Define Data Identifier (0x2C) Service in UDS Protocol?

Here are the reasons why we need Dynamically Define Data Identifier (0x2C) Service in UDS Protocol:

1. Efficient Grouping of Data Identifiers

The 0x2C service allows engineers to define a single custom Data Identifier that groups multiple existing identifiers. Instead of sending separate requests for each piece of data, a tester can request all grouped data at once. This significantly reduces the number of messages sent over the CAN bus. It’s especially helpful when dealing with a large set of related parameters. Grouping improves speed and makes data handling more efficient.

2. Reduced Communication Overhead

Sending multiple individual ReadDataByIdentifier (0x22) requests can create unnecessary bus traffic and increase diagnostic session delays. By using a dynamically defined identifier, a single 0x22 request can replace many smaller ones. This reduces the load on the network and speeds up data retrieval. It’s ideal for high-frequency testing environments where performance matters. This ultimately leads to smoother and faster diagnostic operations.

3. Flexibility During Testing and Validation

One of the biggest advantages of the 0x2C service is its dynamic nature. It allows testers to define and redefine what data they want to monitor without needing to modify ECU software. This flexibility is extremely valuable during development or troubleshooting phases. Engineers can quickly adapt to changing test scenarios and requirements. It saves time and resources in the long run.

4. Improved Real-Time Monitoring

When multiple data points are monitored in real-time (like speed, temperature, and pressure), delays in retrieving data individually can lead to synchronization issues. Using a dynamically defined identifier ensures all required data is fetched in one go and reflects the same time snapshot. This is critical for accurate measurements and comparisons. It enhances the quality of validation and diagnostics.

5. No Need for Static Configuration Changes

In traditional setups, adding or modifying DIDs requires ECU firmware updates or changes to configuration files. With 0x2C, testers can define new DIDs on the fly, eliminating the need for firmware modification. This makes the diagnostic process much more agile. It is especially beneficial when working with prototypes or pre-production ECUs. This also reduces development downtime and cost.

6. Essential for Advanced Diagnostic Tools

Advanced test benches, calibration tools, and validation systems often need fast, customizable access to ECU data. The 0x2C service enables these tools to create test-specific identifiers without waiting for a new firmware version. It enhances compatibility between diagnostic tools and ECUs. This service bridges the gap between flexibility and control in automotive diagnostics. It’s a key feature for professional diagnostic systems.

7. Supports Custom Test Cases and Use Cases

In development environments, each test case might require access to a unique combination of signals or parameters. With the 0x2C service, engineers can define custom DIDs tailored to specific test requirements without waiting for software updates. This supports faster test cycle iterations and improves test coverage. It’s particularly useful in end-of-line testing, functional validation, or hardware-in-the-loop (HIL) setups.

8. Simplifies Data Logging and Analysis

When logging data from an ECU, having all relevant signals under one identifier simplifies the data capture process. Instead of handling multiple logs from individual DIDs, testers can focus on a unified data stream. This improves post-processing, trend analysis, and report generation. It also ensures consistent timestamps across all signals, making analysis more accurate and reliable.

Syntax of 0x2C SID Request Message Frame Format

Request message definition – sub-function = clearDynamicallyDefinedDataIdentifier

Data Byte	Parameter Name	Byte Value
#1	Dynamically Define Data Identifier Request SID	0x2C
#2	sub-function = [                             definition Type =                             clear Dynamically Defined Data Identifier ]	0x03
#3 #4	Dynamically Defined Data Identifier[] = [                                            byte#1 (MSB)                                           byte#2 (LSB) ]	0xF2 / 0xF3 0x00 – 0xFF
C: If this parameter is present, the server must clear the “dynamically Defined Data Identifier” included in byte#1 and byte#2. If the parameter is not present, all “dynamically Defined Data Identifier” in the server shall be cleared.

Request Message Data-Parameter

dynamicallyDefinedDataIdentifier

This parameter defines how the dynamic data record will be referenced in future ReadDataByIdentifier or ReadDataByPeriodicDataIdentifier calls. It should be treated as a dataIdentifier in ReadDataByIdentifier and as a periodicRecordIdentifier in ReadDataByPeriodicDataIdentifier. For periodic requests, refer to the ReadDataByPeriodicDataIdentifier service for specific requirements.

Syntax of 0x2C SID Positive Response Message Frame Format

Data Byte	Parameter Name	Byte Value
#1	Dynamically Define Data Identifier +Ve Response SID	0x6C
#2	sub-function = [ definition Type ]	0x00 – 0x7F
#3 #4	Dynamically Defined Data Identifier [] = [                                                    byte#1 (MSB)                                                   byte#2 (LSB) ]	0xF2 / 0xF3 0x00 – 0xFF
C: This parameter must be included in the request message if the dynamically Defined Data Identifier parameter is present. Otherwise, the parameter should not be included.

Response Message Data-Parameter

definitionType

This parameter echoes bits 6 through 0 of the sub-function parameter from the request message.

dynamicallyDefinedDataIdentifier

This parameter echoes the data-parameter dynamicallyDefinedDataIdentifier from the request message.

Syntax of 0x2C SID Negative Response Message Frame Format

Data Byte	Parameter Name	Byte Value
#1	Dynamically Define Data Identifier –Ve Response SID	0x7F
#2	Requested SID [ byte#1 ]	0x2C
#3	Negative Response Code[] = [ byte#1 ]	NRC

Sub-Function ID of (0x2C) SID in UDS Protocol

Bits 6 – 0	Parameter Name	Description
00	ISOSAE Reserved	This value is reserved by this document for future definition.
01	Define By Identifier	This value indicates to the server that the definition of the dynamic data identifier should occur through a data identifier reference.
02	Define By Memory Address	This value is intended to instruct the server that the definition of the dynamic data identifier should take place through an address reference.
03	Clear Dynamically Defined Data Identifier	This value is used to clear the specified dynamic data identifier. The server must respond positively to a clear request, even if the identifier doesn’t currently exist. However, the identifier must be within a valid range. If the identifier is being reported periodically, it should first be stopped and then cleared.
04-7F	ISOSAE Reserved	This range of values is set aside by this document for future definition.

Supported Negative Response Codes (NRCs) of 0x2C SID in UDS Protocol

NRC	Parameter Name	Description
0x12	Sub-Function Not Supported	This Negative Response Code (NRC) shall be transmitted if the sub-function parameter is not supported.
0x13	Incorrect Message Length Or Invalid Format	This Negative Response Code (NRC) shall be sent if the length of the message is incorrect.
0x22	Conditions Not Correct	This Negative Response Code (NRC) shall be sent if the operating conditions of the server do not meet the requirements to perform the required action.
0x31	Request Out Of Range	This Negative Response Code (NRC) shall be sent if: • Any data identifier (dynamically Defined Data Identifier or any source Data Identifier) in the request message is not supported/invalid. • The position In Source Data Record was incorrect (less than 1, or greater than the maximum allowed by the server). • Any memory address in the request message is not supported by the server. • The specified memory Size was invalid. • The amount of data to be packed into the dynamic data identifier exceeds the maximum allowed by the server. • The specified address And Length Format Identifier is not valid. • The total length of a dynamically defined periodic Data Identifier exceeds the maximum length that fits into a single frame of the data link used for transmission of the periodic response message.
0x33	Security Access Denied	This Negative Response Code (NRC) shall be sent if: • Any data identifier (dynamically Defined Data Identifier or any source Data Identifier) in the request message is secured, and the server is not in an unlocked state. • Any memory address in the request message is secured, and the server is not in an unlocked state.

Example of Dynamically Define Data Identifier (0x2C) Service in UDS Protocol

Below are the Examples of Dynamically Define Data Identifier (0x2C) Service in UDS Protocol:

Read Data By Identifier Request DDDDI 0xF301 Message Flow Example 1

Message direction	Client → Server
Message Type	Request
Data Byte	Description (all values are in hexadecimal)	Byte Value
#1	Read Data By Identifier Request SID	0x22
#2 #3	Data Identifier [ byte#1 ] (MSB) Data Identifier [ byte#2 ] (LSB)	0xF3 0x01

Read Data By Identifier Positive Response DDDDI 0xF301 Message Flow Example 1

Message direction	Server → Client
Message Type	Response
Data Byte	Description (all values are in hexadecimal)	Byte Value
#1	Read Data By Identifier +Ve Response SID	0x62
#2 #3	Data Identifier [ byte#1 ] (MSB) Data Identifier [ byte#2 ] (LSB)	0xF3 0x01
#4 #5 #6 #7 #8 #9 #10	Data Record [ data#1 ] = EOT Data Record [ data#2 ] = EOT Data Record [ data#3 ] = AAT Data Record [ data#4 ] = EOL Data Record [ data#5 ] = EOL Data Record [ data#6 ] = EOL Data Record [ data#7 ] = EOL	0x4C 0x36 0x4D 0x49 0x21 0x00 0x17

Read Data By Identifier Negative Response DDDDI 0xF301 Message Flow Example 1

Message direction	Server → Client
Message Type	Response
Data Byte	Description (all values are in hexadecimal)	Byte Value
#1	Read Data By Identifier –Ve Response SID [ byte#1 ]	0x7F
#2	Requested SID [ byte#1 ]	0x22
#3	Negative Response Code [ byte#1 ]	NRC

Read Data By Identifier Request DDDDI 0xF302 Message Flow Example 2

Message direction	Client → Server
Message Type	Request
Data Byte	Description (all values are in hexadecimal)	Byte Value
#1	Read Data By Identifier Request SID	0x22
#2 #3	Data Identifier [ byte#1 ] (MSB) Data Identifier [ byte#2 ] (LSB)	0xF3 0x02

Read Data By Identifier Positive Response DDDDI 0xF302 Message Flow Example 2

Message direction	Server → Client
Message Type	Response
Data Byte	Description (all values are in hexadecimal)	Byte Value
#1	Read Data By Identifier +Ve Response SID	0x62
#2 #3	Data Identifier [ byte#1 ] (MSB) Data Identifier [ byte#2 ] (LSB)	0xF3 0x02
#4 #5 #6 #7 #8	Data Record [ data#1 ] = ECT Data Record [ data#2 ] = RPM Data Record [ data#3 ] = RPM Data Record [ data#4 ] = IAC Data Record [ data#4 ] = KS	0xA6 0x07 0x50 0x82 0x91

Read Data By Identifier Negative Response DDDDI 0xF302 Message Flow Example 2

Message direction	Server → Client
Message Type	Response
Data Byte	Description (all values are in hexadecimal)	Byte Value
#1	Read Data By Identifier –Ve Response SID [ byte#1 ]	0x7F
#2	Requested SID [ byte#1 ]	0x22
#3	Negative Response Code [ byte#1 ]	NRC

// Below example shows how to use the UDS commands over the CAN data field as per the DoCAN
// Example for Positive Response for SID-0x2C
Request: Client --> Server
02 2C 03
Positive Response: Server --> Client
02 6C 03
// Example for Negative Response for SID-0x2C
Request: Client --> Server
03 2C 03
Negative Response: Server --> Client
03 7F 2C 13

Understanding UDS Service 0x2C Commands Over CAN (DoCAN) – With Examples

In UDS (Unified Diagnostic Services), the Service ID 0x2C is used to Dynamically Define Data Identifiers (DIDs). This allows testers to group multiple existing DIDs into a single identifier, which can later be used to read multiple parameters at once.

The communication between a client (tester tool) and server (ECU) happens over CAN, following the DoCAN (Diagnostics over CAN) standard. Let’s break down some real examples to understand how this service works at the byte level.

✅ Example 1: Positive Response for SID 0x2C

Request from Client to Server:

02 2C 03

• 02 → Number of additional bytes (Service ID and Sub-function).
• 2C → Service ID for Dynamically Define Data Identifier.
• 03 → Sub-function value. In this case, it means “Define By Memory Address (0x03)”, which tells the ECU that memory addresses will be used for the new dynamic DID.

Positive Response from Server to Client:

02 6C 03

• 02 → Number of additional bytes (in the response).
• 6C → Positive response Service ID for 0x2C (it’s 0x2C + 0x40 = 0x6C).
• 03 → Echoes the sub-function that was accepted and processed correctly.

This tells us that the ECU has successfully accepted the dynamic DID definition using memory addresses.

❌ Example 2: Negative Response for SID 0x2C

Request from Client to Server:

03 2C 03

• 03 → Number of additional bytes (meaning more data may follow, but is likely incomplete or incorrect).
• 2C → Service ID for Dynamically Define Data Identifier.
• 03 → Sub-function: Define by memory address.

Negative Response from Server to Client:

03 7F 2C 13

• 03 → Number of bytes in the response (standard for negative response).
• 7F → Negative response indicator in UDS.
• 2C → The service ID that failed (so the client knows what failed).
• 13 → NRC (Negative Response Code) = 0x13, which means “Invalid Format”.

So in this case, the ECU is rejecting the request because the format is incorrect possibly because the message was incomplete, or data length did not match the expected structure.

Advantages of Dynamically Define Data Identifier (0x2C) Service in UDS Protocol

These are the Advantages of Dynamically Define Data Identifier (0x2C) Service in UDS Protocol:

1. Efficient Data Grouping: Allows multiple DIDs to be combined under one dynamic identifier, reducing the number of requests sent to the ECU. This is helpful when testing needs data from several sensors or memory locations. It organizes communication better and simplifies the workflow. Instead of polling individual signals, one grouped response delivers all values. This improves speed and consistency. It’s ideal for test automation and real-time analysis.
2. Reduced CAN Bus Load: By grouping requests, the service lowers the total number of CAN frames used. This reduces traffic on the bus, making it more efficient. Especially in busy networks, this helps prevent overload or delays. It conserves bandwidth and supports more stable communication. It’s a smart way to optimize ECU communication in multi-node systems.
3. High Flexibility in Testing: Testers can define custom DIDs during runtime without changing the firmware. This makes it easy to adapt to various test cases or vehicles. It supports quick prototyping and dynamic configuration. No need to wait for ECU updates to read new data. It speeds up debugging and validation, making development agile.
4. Real-Time Data Synchronization: All signals grouped under a dynamic DID are returned together, ensuring synchronization. This is useful when comparing fast-changing values like RPM, temperature, or sensor feedback. Having them in one frame avoids timing mismatches. It ensures the data snapshot is consistent. That’s critical for safety and performance diagnostics.
5. No Need for Firmware Update: Traditional DIDs require updates to ECU software when new data points are added. With 0x2C, dynamic identifiers can be defined externally. This removes dependency on firmware changes. Testing becomes more independent from development cycles. It also reduces software maintenance and speeds up project timelines.
6. Improved Diagnostic Performance: Combining data requests into one improves round-trip time. It shortens communication cycles and provides faster responses. This leads to quicker test executions and better resource usage. Ideal for high-speed diagnostics or stress testing. Overall, it boosts ECU responsiveness during development.
7. Customized Data Access: Engineers can create dynamic DIDs with only the signals relevant to their specific test. This focused approach helps reduce data noise. It also simplifies interpretation of test results. Custom combinations are more meaningful and easier to analyze. This supports more accurate root cause analysis and faster troubleshooting.
8. Simplified Logging and Monitoring: Dynamic DIDs can include only the signals needed for a log or trace. This makes logs cleaner and smaller in size. It reduces post-processing time and simplifies visualization. Tools can display grouped values more intuitively. Great for in-vehicle testing or performance benchmarking.
9. Support for Advanced Tools: Modern diagnostic tools can leverage 0x2C to build reusable templates. These templates can be applied across different vehicle variants. It enhances tool automation and testing repeatability. The service integrates well with automated HIL or SIL systems. This makes testing scalable and cost-effective.
10. Enhanced Development Workflow: Developers and testers save time by not needing to coordinate firmware changes just to read additional data. The workflow becomes faster and less dependent on software teams. Communication is more streamlined. Diagnostics are easier to configure and run. It supports agile development and rapid validation cycles.

Disadvantages of Dynamically Define Data Identifier (0x2C) Service in UDS Protocol

These are the Disadvantages of Dynamically Define Data Identifier (0x2C) Service in UDS Protocol:

1. Limited Support in Some ECUs: Not all ECUs implement the 0x2C service, especially in older vehicles or basic control units. This limits its usability across platforms. Developers might face compatibility issues during testing. Custom firmware support might be required, which increases effort. Tool chains may also need updates to handle this service effectively.
2. Requires Careful Configuration: Defining incorrect or unsupported DIDs can lead to unexpected negative responses. It demands detailed knowledge of the ECU’s memory and signal mapping. Misconfiguration can result in invalid data or communication failures. Thorough documentation is necessary. It increases the risk of human error during test setup.
3. Security Concerns: Allowing dynamic access to internal data can pose security risks if not properly protected. Attackers could exploit this feature to access sensitive vehicle information. Secure access control and session handling are essential. Improper implementation may open vulnerabilities. It needs to be managed carefully in safety-critical systems.
4. Not Suitable for Production Use: The service is mainly intended for testing and diagnostics, not for regular operation. Using dynamic DIDs in production systems can lead to inconsistent behavior. It’s not meant for permanent data access logic. This limits its application to the development and validation phases only. Engineers must switch to static DIDs for production readiness.
5. Increased Development Complexity: Managing dynamic DIDs adds complexity to test scripts and automation tools. Tools must handle configuration and mapping dynamically, which adds logic overhead. Debugging also becomes harder if signal grouping is inconsistent. This may lead to slower development cycles in the beginning. A strong test framework is required to support it properly.
6. Potential Memory Constraints: Some ECUs may have limited resources to support multiple dynamic DIDs. Defining too many at once might exhaust memory or stack space. This can cause errors or slowdowns. Careful resource planning is needed when using the feature heavily. It may not scale well in memory-constrained microcontrollers.
7. Lack of Standardized Signal Mapping: Each OEM or supplier may define signals differently within their ECUs. This inconsistency requires testers to customize the dynamic DIDs per platform. It reduces reusability of test cases across different vehicle models. Maintaining mapping documentation becomes necessary. It increases overhead for validation teams.
8. Complex Session Management: Dynamic DIDs often require elevated diagnostic sessions, such as extended or programming modes. Managing these sessions correctly is essential. Misuse can result in session timeout or loss of communication. It complicates the testing setup, especially when switching between different ECUs. This adds layers to test case design.
9. Harder Traceability: Since dynamic DIDs are created at runtime, it can be harder to trace issues back to specific signals. Log files may not clearly indicate what each dynamic DID contains. Analysts need extra mapping references. This makes post-analysis and debugging slightly more tedious. Static DIDs provide more clarity in this regard.
10. Tool Dependency: Not all diagnostic tools support defining or interpreting dynamic DIDs effectively. Legacy tools may not recognize 0x2C service at all. This limits flexibility and may require toolchain upgrades. It also creates a dependency on vendor-specific implementations. This could increase testing costs in some setups.

Future Development and Enhancement of Dynamically Define Data Identifier (0x2C) Service in UDS Protocol

Here are the Future Development and Enhancement of Dynamically Define Data Identifier (0x2C) Service in UDS Protocol:

1. Broader ECU Support: Future ECUs can be designed with native support for the 0x2C service across all control units. This would enhance test coverage and consistency during diagnostics. Making it a standard feature across OEMs will increase usability. It also improves the flexibility of testing in a unified way. Widespread implementation could reduce compatibility concerns.
2. Improved Security Handling: Enhancing security measures for dynamic DIDs like session-based access control and encryption can make the 0x2C service safer. Future implementations may include authentication layers to prevent misuse. These measures will help mitigate data leaks and cyber threats. It can also make dynamic access compliant with automotive cybersecurity standards like ISO/SAE 21434.
3. Dynamic DID Visualization Tools: Upcoming diagnostic tools may offer visual dashboards to define and monitor dynamic DIDs. This could simplify the entire configuration process. Real-time signal mapping with a user-friendly interface would reduce manual errors. It would also aid faster debugging and training for new engineers. Visual tools make diagnostics more intuitive and accessible.
4. Support for Nested Data Structures: Currently, dynamic DIDs are often limited to flat or basic data structures. Future enhancements may include support for arrays, nested objects, or grouped signals. This allows more complex and structured diagnostics. It can improve the richness of the data retrieved. Developers could simulate real-world operating conditions better.
5. Cloud-Based Diagnostics Integration: With cloud diagnostics becoming more common, dynamic DID definitions may be synced across systems. Cloud-based test plans and remote monitoring could utilize the 0x2C service. This will help teams manage updates and testing in distributed environments. It also supports continuous diagnostics without local setups. Cloud features would enhance scalability and collaboration.
6. Enhanced Interoperability Standards: Future improvements could involve standardizing signal naming and mapping for dynamic DIDs across OEMs. This can simplify tool compatibility and reuse across platforms. A shared library of signal definitions can increase productivity. It will also help testers switch between vehicle models more easily. Better interoperability reduces development friction.
7. Integration with AI/ML Testing Tools: As AI-driven diagnostics evolve, tools could automatically generate dynamic DID requests based on fault patterns. This allows for predictive testing and smarter debugging. AI systems may learn optimal grouping of signals to define DIDs dynamically. It would improve efficiency and reduce manual work. This marks a shift toward intelligent diagnostics.
8. Automatic Rollback Mechanisms: A future enhancement could include rollback features for incorrectly defined DIDs. This would allow ECUs to revert to a safe state automatically. It adds reliability to test environments and reduces the risk of failed diagnostics. Error recovery becomes smoother. It’s a useful safeguard in experimental setups.
9. Standardized Test Automation APIs: Tool vendors might develop standardized APIs to automate the use of the 0x2C service in test scripts. This enables integration into CI/CD pipelines for automotive testing. It supports faster validation cycles. Developers won’t need to manually configure DIDs. Such APIs promote a programmable and scalable testing workflow.
10. Better Memory and Resource Optimization: New ECU architectures could allocate dynamic memory blocks more efficiently for defined DIDs. This avoids overflow or performance issues when using multiple DIDs. Dynamic memory handling techniques like garbage collection may be integrated. It ensures reliable and smooth diagnostics even in constrained systems. Memory management will become more adaptive and intelligent.