Read Data By Periodic Identifier (0x2A) Service in UDS Protocol

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blank" rel="noreferrer noopener">UDS 0x2A – a powerful and often-used service in the UDS protocol: Read Data By Periodic Identifier (0x2A). This service allows the ECU to send requested data automatically at regular intervals without repeated requests. It’s especially useful for real-time monitoring, diagnostics, and system performance tracking in vehicles. In this post, I’ll explain how the 0x2A service works, how to configure it, and where it’s commonly used. You’ll also learn about the communication flow, key parameters, and use cases in automotive ECUs. By the end, you’ll have a clear understanding of this UDS service and how it benefits vehicle diagnostics!

Introduction to Read Data By Periodic Identifier (0x2A) Service in UDS Protocol

The Read Data By Periodic Identifier (0x2A) service in the UDS (Unified Diagnostic Services) protocol allows diagnostic testers to receive specific data from the ECU at fixed time intervals without repeatedly sending requests. This makes it highly efficient for real-time data monitoring and system diagnostics in automotive applications. Service 0x2A is commonly used to track values like engine temperature, RPM, or sensor status continuously during a test session. It reduces communication overhead while ensuring critical information is updated consistently. Understanding how this service works is essential for professionals working on vehicle diagnostics, ECU programming, and automotive communication systems.

What is Read Data By Periodic Identifier (0x2A) Service in UDS Protocol?

The Read Data By Periodic Identifier (Service 0x2A) is a diagnostic service defined in the UDS (Unified Diagnostic Services) protocol, specified under the ISO 14229 standard. It is used to request the ECU (Electronic Control Unit) to automatically send specific diagnostic data at regular time intervals without the tester having to repeatedly send read requests.

Purpose:

This service is designed to reduce the communication load between the tester and the ECU by allowing periodic transmission of data. It is especially useful during real-time monitoring, data logging, or functional testing where specific parameters (like RPM, temperature, or speed) need to be tracked continuously.

Why do we need Read Data By Periodic Identifier (0x2A) Service in UDS Protocol?

In vehicle diagnostics, testers often need to monitor specific ECU parameters continuously, such as engine RPM, coolant temperature, throttle position, or sensor data. Normally, this would require sending repeated ReadDataByIdentifier (0x22) requests to fetch each value again and again. However, this approach:

• Consumes a lot of bus bandwidth
• Increases latency
• Generates unnecessary communication overhead
• Puts more processing load on both tester and ECU

To solve this problem, UDS provides the 0x2A service, which allows the tester to request certain DIDs (Data Identifiers) once, and then the ECU automatically transmits the data periodically at defined intervals.

1. Reduces Communication Traffic

Using the 0x2A service minimizes the number of diagnostic requests sent from the tester to the ECU. Instead of repeatedly asking for the same data using 0x22 requests, the tester can send one 0x2A request, and the ECU will keep sending the required data automatically. This significantly reduces bus traffic, especially during high-frequency monitoring. It is very useful in environments where bandwidth is limited, such as on a CAN network. This reduction in communication overhead helps maintain better overall bus performance.

2. Improves Data Retrieval Efficiency

The 0x2A service ensures data is delivered at consistent intervals, without the need for manual polling. It simplifies the process for the diagnostic tester, which no longer needs to manage polling timers or wait for ECU responses. The ECU itself handles data transmission timing, making the process more efficient. This is particularly important during continuous testing or validation procedures. As a result, testers can focus more on analysis rather than managing communication sequences.

3. Supports Real-Time Monitoring

In use cases like vehicle road testing or hardware-in-the-loop (HIL) simulations, testers need to observe changing vehicle parameters in real time. Service 0x2A provides a stable method to receive frequent updates of live data like speed, RPM, or temperature. Real-time feedback is critical for detecting anomalies, calibrating ECUs, and verifying functionality under different conditions. By using 0x2A, engineers can ensure timely data flow without interruption or manual intervention.

4. Simplifies Tester Software Design

The tester tool or software doesn’t need to implement complex timing logic to continuously send read requests. With 0x2A, once the periodic data stream is activated, the tool simply waits to receive updates. This streamlines software development and testing workflows. It also reduces the risk of timing errors or missed updates that could happen with manual polling. Overall, it leads to a cleaner and more robust test environment.

5. Provides Consistent and Predictable Data Timing

Since the ECU sends the data at fixed intervals, the tester receives consistent, evenly spaced data samples. This predictability helps ensure that graphs, logs, or real-time displays reflect actual system behavior accurately. Consistent timing is especially important in performance benchmarking and timing-critical diagnostics. In contrast, manual polling may lead to jitter or missed data points due to varying request intervals.

6. Enhances ECU Resource Utilization

With periodic transmission managed internally by the ECU, the system avoids handling numerous incoming read requests. This leads to better resource management inside the ECU, as it can pre-schedule data delivery instead of responding to random incoming requests. It minimizes processing overhead and allows the ECU to focus on core tasks like control algorithms and sensor management. Especially in safety-critical systems, this efficient use of resources helps maintain system stability and performance.

7. Ideal for Long-Duration Testing and Logging

During long-term vehicle testing, such as endurance runs or environmental chamber testing, engineers often need to log data over hours or days. The 0x2A service enables this by ensuring that important parameters are streamed continuously without any manual intervention. This makes it easier to collect large datasets with uniform sampling intervals. It also reduces the chance of human or tool-related errors during extended test scenarios, ensuring data integrity.

Syntax of 0x2A SID Request Message Frame Format

Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Read Data By Periodic Identifier Request SID	0x2A
#2	Transmission Mode	0x00 – 0xFF
#3	Periodic Data Identifier[]#1	0x00 – 0xFF
:	:	:
#m+2	Periodic Data Identifier[]#m	0x00 – 0xFF
C: When the transmission mode is set to ‘send At Slow Rate’, ‘send At Medium Rate’, or ‘send At Fast Rate’, the first periodic data identifier must be included in the request message. However, if the transmission mode is ‘stop Sending’, there are two possibilities: either no periodic data identifier is present, indicating the halt of all scheduled periodic data identifiers, or the client can explicitly specify one or more periodic data identifiers to be stopped.

Request Message Data-Parameter

transmissionMode

This parameter specifies the transmission rate for the requested periodicDataIdentifiers to be used by the server.

periodicDataIdentifier (#1 to #m)

This parameter identifies the server data record(s) requested by the client. Multiple periodicDataIdentifiers can be requested in a single request.

Syntax of 0x2A SID  Positive Response Message Frame Format

Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Read Data By Periodic Identifier Request SID	0x6A

Syntax of 0x2A SID Negative Response Message Frame Format

Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Read Data By Periodic Identifier Request SID [ byte#1 ]	0x7F
#2	Requested SID [ byte#1 ]	0x2A
#3	Negative Response Code [ byte#1 ]	NRC

Syntax of 0x2A SID Periodic Data Response Message Data Definition

Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Periodic Data Identifier	0x00 – 0xFF
#2 : #k+2	Data Record[] = [                                data#1                               :                                data#k ]	0x00 – 0xFF : 0x00 – 0xFF

Periodic Message Data-Parameter

periodicDataIdentifier

This parameter references a periodicDataIdentifier from the request message.

dataRecord

This parameter is used in the ReadDataByPeriodicIdentifier positive response message to provide the requested data record values to the client. The content of the dataRecord is not defined in this document and is specific to the vehicle manufacturer.

Supported Negative Response Codes (NRCs) of 0x2A SID

NRC	Parameter Name	Description
0x13	Incorrect Message Length Or Invalid Format	This NRC (Negative Response Code) is transmitted if the length of the request message is invalid or if the client has exceeded the maximum number of periodic Data Identifiers allowed to be requested at a given time.
0x22	Conditions Not Correct	This NRC (Negative Response Code) is transmitted if the operating conditions of the server do not meet the requirements to perform the requested action. For example, this could happen if the client requests periodic Data Identifiers with different transmission Modes, and the server does not support multiple transmission Modes simultaneously.
0x31	Request Out Of Range	This NRC (Negative Response Code) is sent if: •None of the requested periodic Data Identifier values are supported by the device. •None of the requested periodic Data Identifiers are supported in the current session. •The specified transmission Mode is not supported by the device. •The requested dynamic Defined Data Identifier has not been assigned yet. •The client exceeded the maximum number of allowed concurrent scheduled periodic Data Identifiers.
0x33	Security Access Denied	This NRC (Negative Response Code) is sent if at least one of the periodic Data Identifiers is secured, and the server is not in an unlocked state.

Example of Read Data By Periodic Identifier (0x2A) Service in UDS Protocol

Below are the Examples of Read Data By Periodic Identifier (0x2A) Service in UDS Protocol:

Step #1: Request Periodic Transmission of the Periodic Data Identifiers

Read Data By Periodic Identifier Request Message Flow Example – step #1

Message Direction	Client → Server
Message Type	Request
Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Read Data By Periodic Identifier Request SID	0x2A
#2	Transmission Mode = send At Medium Rate	0x02
#3	Periodic Data Identifier#1	0xE3
#4	Periodic Data Identifier#2	0x24

Read Data By Periodic Identifier Initial Response Message Flow Example – Step #1

Positive Response:

Message Direction	Server → Client
Message Type	Response
Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Read Data By Periodic Identifier +Ve Response SID	0x6A

Negative Response:

Message Direction	Server → Client
Message Type	Response
Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Read Data By Periodic Identifier –Ve Response SID [ byte#1 ]	0x7F
#2	Requested SID [ byte#1 ]	0x2A
#3	Negative Response Code [ byte#1 ]	NRC

Read Data By Periodic Identifier Sub-Sequent Positive Response Message #1 Flows – Step #1

Message Direction	Server → Client
Message Type	Response
Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Periodic Data Identifier#2	0xE3
#2 #3 #4 #5 #6	Data Record [ data#1 ] = ECT Data Record [ data#2 ] = TP Data Record [ data#3 ] = RPM Data Record [ data#4 ] = RPM Data Record [ data#5 ] = VSS	0xA6 0x66 0x07 0x50 0x00

Read Data By Periodic Identifier Sub-Sequent Negative Response Message #1 Flows – Step #1

Message Direction	Server → Client
Message Type	Response
Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Periodic Data Identifier#2 [ byte#1 ]	0x7F
#2	Requested SID [ byte#1 ]	0x2A
#3	Negative Response Code [ byte#1 ]	NRC

Read Data By Periodic Identifier Sub-Sequent Positive Response Message #2 Flows – Step #1

Message Direction	Server → Client
Message Type	Response
Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Periodic Data Identifier#2	0x24
#2 #3 #4 #5 #6	Data Record [ data#1 ] = B+ Data Record [ data#2 ] = MAP Data Record [ data#3 ] = MAF Data Record [ data#4 ] = BARO Data Record [ data#5 ] = LOAD	0x8C 0x20 0x1A 0x63 0x4A

Read Data By Periodic Identifier Sub-Sequent Negative Response Message #2 Flows – Step #1

Message Direction	Server → Client
Message Type	Response
Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Periodic Data Identifier#2 [ byte#1 ]	0x7F
#2	Requested SID [ byte#1 ]	0x2A
#3	Negative Response Code [ data#1 ]	NRC

Step #2: Stop the Transmission of the Periodic Data Identifiers

Read Data By Identifier Request Message Flow Example – Step #2

Message Direction	Client → Server
Message Type	Request
Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Read Data By Periodic Identifier Request SID	0x2A
#2	Transmission Mode = stop Sending	0x04
#3	Periodic Data Identifier#1	0xE3

Read Data By Identifier Response Message Flow Example – Step #2

Positive Response:

Message Direction	Server → Client
Message Type	Response
Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Read Data By Periodic Identifier +Ve Response SID	0x6A

Negative Response:

Message Direction	Server → Client
Message Type	Response
Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Read Data By Periodic Identifier –Ve Response SID	0x7F
#2	Requested SID [ byte#1 ]	0x2A
#3	Negative Response Code [ byte#1 ]	NRC

Example of Read Data By Periodic Identifier (0x2A) SID Request and Positive Response Frame Format

Request Frame Format:

PCI Length	SID	Transmission Mode (Fast Mode)	DID (Over Speed)
0x04	0x2A	0x03	F9	08

Positive Response Frame Format:

PCI Length	Positive Response	DID		Data
0x05	6A	F9	08	66	0A

Example of Read Data By Periodic Identifier (0x2A) SID Request and Negative Response Frame Format

Request Frame Format:

PCI Length	SID	Transmission Mode (Fast Mode)	DID (Over Speed)
0x05	0x2A	0x03	F9	08

Negative Response Frame Format:

PCI Length	Negative Response	SID	NRC
0x03	7F	2A	13

Advantages of Read Data By Periodic Identifier (0x2A) Service in UDS Protocol

Following are the Advantages of Read Data By Periodic Identifier (0x2A) Service in UDS Protocol:

1. Automatic Data Transmission: The Read Data By Periodic Identifier (0x2A) service allows the ECU to automatically send diagnostic data at regular intervals after receiving a single request. This means the tester does not have to repeatedly send Read Data By Identifier (0x22) requests. Once activated, the data flow continues until a stop command is issued. This feature simplifies the diagnostic process and saves time. It’s especially helpful in automated testing environments.
2. Reduced Network Load: Continuous polling using 0x22 service increases bus traffic and consumes more bandwidth. With 0x2A, since data is sent periodically without repeated requests, the communication load on the CAN network is significantly reduced. This allows other control and diagnostic messages to flow freely. Lower bus load leads to better performance and more efficient diagnostics. It also helps avoid message collisions or delays.
3. Real-Time Monitoring Support: This service is ideal for monitoring parameters such as engine speed, temperature, or battery voltage in real-time. Engineers can receive constant data updates without pausing the test or resending requests. Real-time visibility is crucial during vehicle road tests or functional validation. It enables quick decision-making and problem detection. Such live data access improves efficiency in development and testing.
4. Improved Timing Accuracy: With polling-based approaches, timing can vary due to request/response delays. The 0x2A service ensures that data is transmitted at fixed intervals, making timing highly consistent. This accuracy is important for applications where signal synchronization is critical. Engineers can reliably track changes over time or compare multiple parameters. The result is more precise analysis and data logging.
5. Simplified Tester Implementation: Instead of writing complex logic to send repeated requests and manage responses, the tester tool only needs to send a single request to initiate periodic data. The ECU handles the rest, sending responses at regular intervals. This reduces the tester’s software complexity and potential for timing-related bugs. It also shortens development time for test tools. A simpler system is easier to maintain and debug.
6. Better ECU Load Management: When the ECU is bombarded with frequent 0x22 requests, it consumes more processing power. With 0x2A, the ECU handles data reporting in a scheduled and managed way. This allows it to balance resources more efficiently. As a result, the ECU remains responsive and stable during diagnostics. This approach ensures that real-time control functions are not affected by diagnostics.
7. Ideal for Continuous Data Logging: In long-duration testing, such as endurance or environmental tests, uninterrupted data collection is essential. The 0x2A service keeps sending data at fixed intervals, ensuring consistent and complete logs. Engineers can collect large datasets without worrying about missed values or communication gaps. It’s a reliable way to monitor performance over time. This is particularly useful in OEM-level testing and validation.
8. Multiple Data Identifiers Support: The service can be configured to send multiple Data Identifiers (DIDs) in one periodic transmission. This reduces the number of separate diagnostic messages needed and improves data efficiency. For example, instead of requesting RPM, coolant temp, and voltage separately, they can all be bundled together. This saves time and bus bandwidth. It also simplifies test script creation.
9. Predictable Data Flow for Visualization: Graphing tools and dashboards rely on regular, evenly spaced data to produce smooth and accurate visuals. Since 0x2A ensures predictable timing, the data received is consistent, which improves the quality of real-time graphs and trends. This helps engineers visually detect anomalies or patterns during analysis. It also avoids confusion caused by irregular updates.
10. Early Fault Detection and Health Monitoring: By continuously monitoring key parameters, engineers can detect deviations from normal behavior as they happen. For example, sudden drops in fuel pressure or rising engine temperature can be flagged instantly. This proactive monitoring helps prevent failures before they escalate. It also supports better maintenance and reliability. Over time, it leads to safer and more efficient vehicles.

Disadvantages of Read Data By Periodic Identifier (0x2A) Service in UDS Protocol

Following are the Disadvantages of Read Data By Periodic Identifier (0x2A) Service in UDS Protocol:

1. Limited by ECU Capabilities: Not all ECUs support the 0x2A service due to resource constraints or software limitations. If the service is unsupported, attempts to use it may result in negative responses. This makes it less universal compared to the more commonly implemented 0x22 service. Engineers must verify ECU capabilities before using this service. This adds an extra compatibility step during testing.
2. Possible Network Overload if Misconfigured: If periodic messages are configured too frequently or with too many Data Identifiers (DIDs), they can saturate the CAN bus. This could interfere with normal ECU operations or other critical communication. Proper timing and data size planning are required to avoid network congestion. Careless use of 0x2A may degrade overall vehicle performance. Always validate transmission intervals during development.
3. Data Flooding Risk: Once initiated, periodic transmission continues until explicitly stopped by the tester. If the stop message is forgotten or missed, the ECU will keep sending data unnecessarily. This leads to unnecessary bus load and storage overflow in logging tools. It can also cause confusion if the tester is restarted and forgets to stop the old session. Proper session management is essential to avoid data flooding.
4. Complex Session Handling: The service typically works only in specific diagnostic sessions, such as extended or programming session. This adds complexity to the tool logic, requiring session changes before initiating 0x2A. Forgetting to switch sessions can result in errors or rejected requests. Managing session transitions correctly becomes critical in automated scripts. Inconsistent session use can lead to false test results.
5. Increased ECU Load if Overused: While this service can reduce request load, the ECU still needs to prepare and send data at regular intervals. If many DIDs are requested periodically, it can burden the processor. Overuse in multiple tools at the same time may reduce ECU responsiveness. It’s crucial to limit how many periodic identifiers are active simultaneously. Efficient configuration avoids overloading the ECU.
6. Diagnostic Tool Dependency: The responsibility to stop periodic transmissions lies with the diagnostic tool. If the tester crashes, loses connection, or fails to stop transmission, the ECU keeps sending data. This can persistently clutter the bus until the next power cycle. Recovery requires manual intervention or robust error handling. The tool must implement fail-safe mechanisms for cleanup.
7. Security Considerations: Some DIDs may expose sensitive or safety-critical data. Periodic transmission of such values can be misused if access isn’t restricted. Attackers could exploit this to monitor or manipulate system behavior. Therefore, OEMs must carefully control which DIDs are allowed under 0x2A. Implementing access levels and session control is important for data protection.
8. Not Ideal for Event-Triggered Data: This service is time-based, not event-based. It cannot adapt to changes in system behavior, like sending data only when thresholds are crossed. In scenarios where updates are only needed during specific events, 0x2A wastes bandwidth. Event-driven services or custom implementations may be more efficient. Choosing the right service based on use case is key.
9. Diagnostic Session Timeout Risk: Since the periodic messages do not count as active tester requests, the session timer may expire during long test runs. When the session times out, the ECU may silently stop sending data or terminate communication. This leads to loss of data unless the tester periodically resets the session timer. Timer management must be integrated with the periodic flow.
10. Difficult Debugging in Multi-Tool Environments: If multiple diagnostic tools are connected and one tool initiates a periodic stream, it may confuse other tools or engineers. Without clear indication, identifying the source of periodic traffic becomes challenging. This complicates debugging and test validation. A centralized tool management policy is needed to prevent conflicts.

Future Development and Enhancement of Read Data By Periodic Identifier (0x2A) Service in UDS Protocol

Below are the Future Development and Enhancement of Read Data By Periodic Identifier (0x2A) Service in UDS Protocol:

1. Adaptive Timing Control: Future versions of the UDS protocol or OEM-specific implementations may support dynamic adjustment of periodic intervals based on vehicle conditions. This would help in reducing unnecessary bus load during idle states and increase update rates during critical events. Adaptive control makes data flow more efficient and context-aware. Such enhancements could be negotiated automatically between the tester and ECU.
2. Event-Driven Periodic Transmission: There is potential for combining periodic data transmission with event-based triggers. Instead of fixed-rate transmission, the ECU could start or adjust the rate of periodic messages based on predefined events like temperature rise or system faults. This hybrid approach would enhance real-time diagnostics without flooding the CAN bus. It also aligns better with smart diagnostics and predictive maintenance.
3. Secure Periodic Data Access: With growing concerns around cybersecurity in connected vehicles, future UDS implementations may incorporate encrypted periodic data or restrict access using authenticated sessions. Enhanced security mechanisms would protect sensitive data from unauthorized tools. This would make periodic transmission more compliant with global automotive security standards like ISO/SAE 21434.
4. Better Integration with Telematics and Cloud Diagnostics: Upcoming vehicle architectures increasingly depend on cloud-connected ECUs. The 0x2A service could be enhanced to integrate with telematics units for remote diagnostics. This would allow remote service centers to monitor live data periodically without physically accessing the vehicle. Cloud-based periodic monitoring would aid fleet management and predictive analytics.
5. Enhanced Multi-Tool Coordination: Future development could enable coordination between multiple diagnostic tools to avoid conflicts in using 0x2A. Protocol enhancements may allow broadcasting of active sessions or handshake mechanisms between testers. This prevents bus congestion and improves collaboration in workshop or production-line environments.
6. Improved Session Management Features: Modern implementations may offer automated session refresh while periodic transmission is active. This avoids session timeout issues that currently require manual tester interventions. Keeping the session alive ensures continuous data flow and simplifies long-duration testing without interruptions.
7. Support for More Data Types and Custom DIDs: In future updates, OEMs might allow the use of more complex or user-defined data types with 0x2A. This would support a broader range of diagnostic needs, including structured and nested data. Advanced parsing and encoding strategies could be developed for efficient handling of such data.
8. Integration with Service-Oriented Architecture (SOA): As vehicles adopt SOA and Ethernet-based communication, 0x2A may evolve to fit into diagnostic-over-IP (DoIP) environments. Enhancing this service to work seamlessly with service-based messaging would future-proof its utility in next-gen ECUs and zonal architectures.
9. Toolchain Simulation and Virtual Testing: To accelerate development, future tools could support simulated ECU behavior for 0x2A service. This would allow testers to validate configurations and timing virtually before deploying to real vehicles. Such enhancements would reduce time-to-market and improve testing efficiency.
10. User-Friendly Configuration Interfaces: Future diagnostic tools may provide visual configuration dashboards to easily set up and monitor 0x2A services. Instead of manually crafting UDS frames, engineers could drag and drop DIDs, set intervals, and monitor data in real-time graphs. This would make the service more accessible to all levels of users.