Automotive UDS Transfer Data (0x36): Role in ECU Reprogramming and Memory Handling

Hello, automotive diagnostics enthusiasts! In this blog post, I will introduce you to Transfer Data (0x36) Service in UDS Protocol – one of the most vital and frequently used se

rvices in the UDS protocol: the Transfer Data (0x36) service. This service is a key part of the ECU reprogramming process, enabling efficient transmission of data blocks to a control unit. Whether you’re flashing a new firmware or writing configuration parameters, Transfer Data plays a critical role in memory handling. In this article, I will explain what the 0x36 service does, how it’s structured, and how it fits into the larger diagnostic session. You’ll also learn when and why to use this service in real-world applications. By the end, you’ll have a strong grasp of how Transfer Data helps streamline ECU communications. Let’s dive into the mechanics of UDS 0x36!

Introduction to Transfer Data (0x36) Service in UDS Protocol

The Transfer Data (0x36) service in the UDS (Unified Diagnostic Services) protocol is an essential part of the data transfer phase during ECU reprogramming or memory operations. Once a download or upload request has been initiated using services like Request Download (0x34) or Request Upload (0x35), the Transfer Data service is used to send or receive actual data blocks. This allows a diagnostic tool or tester to transfer large amounts of memory content in smaller, manageable packets, ensuring efficient and reliable communication between the tester and the control unit. The service is designed to be used in sequence, with each message typically containing a block sequence counter for tracking. Transfer Data is widely used in ECU flashing, calibration tasks, and software updates, making it a core part of modern automotive diagnostics and development.

What is Transfer Data (0x36) Service in UDS Protocol?

The Transfer Data (0x36) service in the UDS protocol is used to transfer blocks of data between a diagnostic tester (client) and an Electronic Control Unit (ECU) during programming sessions. It typically follows a Request Download (0x34) or Request Upload (0x35) service, depending on whether data is being written to or read from the ECU memory. Each Transfer Data request contains a block sequence counter and a portion of the data payload, allowing for large data sets to be sent in smaller, sequential blocks. This method ensures that data can be managed reliably and in order, with mechanisms in place to detect missing or out-of-sequence blocks. The ECU responds to each Transfer Data request with an acknowledgment, and once all data is transferred, the Transfer Exit (0x37) service is used to complete the process. This service is vital for secure and structured ECU programming tasks.

Note: This service does not use a sub-function

Why do we need Transfer Data (0x36) Service in UDS Protocol?

Here’s a detailed explanation of why the Transfer Data (0x36) Service is needed in UDS protocol:

1. Facilitates Large Data Handling

The Transfer Data (0x36) service is essential for handling large chunks of data that cannot be transmitted in a single request. It enables data to be split into smaller, manageable blocks, making the communication process between the tester and the ECU more efficient. This is especially important when uploading or downloading large files, such as firmware updates or memory dumps. By transferring data block-by-block, the protocol reduces the chance of communication failures. This segmented approach is also easier to validate and reattempt in case of transmission errors. Hence, it plays a key role in ensuring successful ECU programming or diagnostics.

2. Ensures Ordered Transmission Using Block Counters

Each data block sent using this service includes a sequence counter that helps the receiver verify the correct order of received data. This is crucial in preventing data corruption due to out-of-order blocks or missed transmissions. If a sequence mismatch is detected, the ECU can request a retry of that particular block. This approach avoids the need to restart the entire transmission from the beginning, saving time and bandwidth. Maintaining proper sequencing is essential for tasks like firmware flashing or memory readouts. Thus, block counters bring structure and reliability to the UDS data transfer process.

3. Supports ECU Firmware Updates

Transfer Data is one of the core services used during the flashing or reprogramming of ECUs in vehicles. After initiating a download session using the Request Download (0x34) service, Transfer Data is used to actually transmit the binary or hex file into the ECU memory. Without this service, delivering firmware securely and systematically would be nearly impossible. The block-by-block mechanism enables integrity checks at each stage of the process. It ensures that only valid and complete data is committed to ECU memory. This makes the service vital for secure and accurate ECU software updates.

4. Allows Dynamic Error Detection and Correction

Thanks to its structured block approach, the Transfer Data service allows ECUs to quickly identify and respond to transmission issues. If a data block is corrupted or missing, the ECU can signal the problem and request a resend. This improves the overall robustness of communication, especially in environments prone to electrical interference or signal loss. Such dynamic error handling reduces update failures and avoids unnecessary re-flashing of ECUs. It also supports diagnostics workflows where incomplete or erroneous data could lead to incorrect troubleshooting. Therefore, the service plays a role in system reliability.

5. Supports Bi-Directional Data Movement

While typically used to write data into ECU memory, Transfer Data can also support data movement in reverse when used alongside the Request Upload (0x35) service. This makes it flexible enough for both programming and diagnostic applications. Whether you’re pushing a new configuration or pulling diagnostic logs, this service allows structured and verified data exchange. It’s particularly useful for capturing memory snapshots during issue investigation. With proper session control, Transfer Data ensures safe communication in both directions, strengthening the versatility of UDS in automotive workflows.

6. Minimizes ECU Resource Usage

Transfer Data allows ECUs to process incoming data in small chunks, reducing the need for large memory buffers or high processing power. Each block can be validated and written to memory as it arrives, making the update process more efficient. This is particularly important for low-cost ECUs with limited RAM or flash memory. Since automotive ECUs vary widely in capability, this incremental approach ensures compatibility across a broad range of modules. It also enables smoother updates even in constrained systems. Thus, Transfer Data improves resource management during communication.

7. Maintains Data Security Through Structured Transfer

Structured block transfer allows security mechanisms to be applied at each stage. For example, blocks can be encrypted or signed individually to prevent tampering. It also allows the ECU to verify the authenticity and integrity of each block before accepting it. This layered security is critical when updating safety-critical components like brake systems or ADAS modules. In many implementations, OEMs integrate custom encryption protocols into this step. Therefore, Transfer Data helps secure the end-to-end diagnostic and flashing process.

8. Improves Communication Synchronization

Transfer Data ensures both the tester and ECU remain in sync during the data exchange. With each block confirmation, both devices know the current status of the transfer session. If a disconnection occurs, the session can resume or restart from the last acknowledged block. This prevents incomplete updates and saves time. It also supports better tracking and logging of each update cycle for traceability. In high-reliability automotive systems, such synchronization is crucial for successful ECU maintenance and updates.

9. Provides Flexibility for Custom Logic in ECUs

The Transfer Data service can be customized to suit the specific needs of an OEM. For instance, data blocks can trigger internal routines in the ECU, like partial validation, pre-write checks, or conditional branching. This makes it a highly adaptable mechanism for complex vehicle systems. Engineers can design their flash bootloaders to interpret certain patterns in the blocks for feature activation or calibration. Such flexibility is not available in basic write commands. Therefore, Transfer Data is preferred for modular and programmable systems.

10. Enables Seamless Transition to Transfer Exit (0x37)

After successful data transmission via Transfer Data, the Transfer Exit (0x37) service is used to conclude the session. This final handshake ensures that all data blocks were received and written correctly. If anything is missing, the ECU can reject the session and roll back changes. This confirmation step prevents system failures caused by incomplete data uploads. It also allows final integrity checks before activating new firmware or configurations. Hence, Transfer Data sets the stage for a safe and clean completion of memory operations in UDS.

Syntax of 0x36 SID Request Message Frame Format

Data byte	Parameter Name	Byte Value
#1	Transfer Data Request SID	0x36
#2	Block Sequence Counter	0x00 – 0xFF
#3 : #n	Transfer Request Parameter Record[] = [                                  transfer Request Parameter#1                                                       :                                  transfer Request Parameter#m ]	0x00 – 0xFF : 0x00 – 0xFF
C = Conditional: this parameter is mandatory if a download is in progress.

Request Message Data-Parameter

BlockSequenceCounter

The blockSequenceCounter parameter starts at 0x01 with the first TransferData request after RequestDownload (0x34) or RequestUpload (0x35) and increments by 1 for each subsequent request. It rolls over to 0x00 at 0xFF.

Use Cases:

• Correct Request, No Response: Client retries the request with the same blockSequenceCounter; server identifies it as a repeat and responds without reprocessing.
• Incorrect Request: Server does not respond; client retries with the same blockSequenceCounter; server treats it as a new request.
• Correct Upload Request, No Response: Client retries with the same blockSequenceCounter; server responds using previously stored data.
• Incorrect Upload Request: Server does not respond; client retries with the same blockSequenceCounter; server processes it as a new request.

TransferRequestParameterRecord

This parameter record contains vehicle manufacturer-specific parameters required for data transfer. Its format and length are defined by the manufacturer.

Example: For a download, transferRequestParameterRecord includes the data to be transferred.

Syntax of 0x36 SID Positive Response Message

Data byte	Parameter Name	Byte Value
#1	Transfer Data +Ve Response SID	0x76
#2	Block Sequence Counter	0x00 – 0xFF
#3 : #n	Transfer Response Parameter Record[] = [                              transfer Response Parameter#1                                                       :                              transfer Response Parameter#m ]	0x00 – 0xFF : 0x00 – 0xFF
C = Conditional: this parameter is mandatory if a upload is in progress.

Response Message Data-Parameter

BlockSequenceCounter

This parameter is an echo of the blockSequenceCounter from the request message.

TransferResponseParameterRecord

This parameter contains data required by the client to support data transfer. Its format and length are vehicle manufacturer specific. For a download, it might include a checksum from the server. For an upload, it could include the uploaded data. Note that for a download, it should not duplicate the transferRequestParameterRecord.

Syntax of 0x36 SID Negative Response Message

Data byte	Parameter Name	Byte Value
#1	Transfer Data –Ve Response SID [ byte#1 ]	0x7F
#2	Requested SID [ byte#1 ]	0x36
#3	Negative Response Code [ byte#1 ]	NRC

Supported Negative Response Codes (NRCs) of 0x36 SID in UDS Protocol

NRC	Parameter Name	Description
0x13	Incorrect Message Length Or Invalid Format	This NRC is sent if the length of the message is incorrect, such as when the message length doesn’t meet the requirements of the max Number Of Block Length parameter returned in the positive response to the request Download service.
0x24	Request Sequence Error	The server uses this response code if: • Request Download or Request Upload service is inactive upon receiving this request. • Request Download or Request Upload service is active, but all data determined by memory Size parameter has already been received.
0x31	Request Out Of Range	This NRC is returned if: • The transfer Request Parameter Record has invalid additional control parameters. • The transfer Request Parameter Record doesn’t match the max Number Of Block Length parameter. • The transfer Request Parameter Record doesn’t align with the server’s memory constraints.
0x71	Transfer Data Suspended	This NRC is returned if the length of the download module does not meet the requirements specified by the memory Size parameter sent in the request message of the request Download service.
0x72	General Programming Failure	This NRC is returned if the server detects an error while erasing or programming a memory location in the permanent memory device (e.g., Flash Memory) during the data download process. Note: The server shall accept the repetition of a Transfer Data request message with a block Sequence Counter equal to the one included in the previous Transfer Data request message.
0x73	Wrong Block Sequence Counter	This NRC is returned if the server detects an error in the sequence of the block Sequence Counter.
0x92 / 0x93	Voltage Too High / voltage Too Low	This return code shall be sent if the voltage measured at the primary power pin of the server is outside the acceptable range for downloading data into the server’s permanent memory (e.g., Flash Memory).

Example of Transfer Data (0x36) Service in UDS Protocol

Below are the Examples of Transfer Data (0x36) Service in UDS Protocol:

Example of Transfer Data (0x36) SID Request and Positive Response Frame Format

Request Frame Format:

PCI Length	SID	Block Sequence Counter	Transfer Request Parameter Record
04	36	04	01	30

Positive Response Frame Format:

PCI Length	Response SID	Block Sequence Counter
02	76	04

Example of Transfer Data (0x36) SID Request and Negative Response Frame Format

Request Frame Format:

PCI Length	SID	Block Sequence Counter	Transfer Request Parameter Record (invalid)
05	36	04	FA	10

Negative Response Frame Format:

PCI Length	Response SID	Request SID	NRC
03	7F	36	13

Advantages of Transfer Data (0x36) Service in UDS Protocol

Following are the Advantages of Transfer Data (0x36) Service in UDS Protocol:

1. Efficient Block-Based Transmission: This service enables the transfer of large data in smaller, manageable blocks, which reduces the risk of memory overflow in the ECU. By segmenting the data, it ensures smoother and more reliable communication. Each block can be verified independently, which adds a layer of safety. This approach is especially useful during ECU flashing where stability is critical. It helps maintain the integrity of the process and avoids system crashes.
2. Supports Reliable Flash Programming: Transfer Data is a vital part of the ECU reprogramming process, allowing precise control over what data is written and when. It ensures that each data block is validated before being accepted by the ECU. This minimizes the risk of corrupted memory during firmware updates. It also supports rollback mechanisms in case of a failure. Overall, it adds robustness to the software update workflow.
3. Ensures Data Integrity with Block Counters: Each transferred block includes a block sequence counter, allowing both the client and the ECU to track the order of the data. This mechanism helps in detecting duplicate or missing blocks. If something goes wrong, the ECU can request a retransmission of the specific block. This makes the entire transmission process highly reliable. It is essential for maintaining consistency in critical ECU memory areas.
4. Optimized for Limited ECU Resources: Since data is broken into smaller blocks, the ECU doesn’t need to allocate large chunks of memory at once. This is particularly helpful in resource-constrained embedded systems. Processing smaller blocks also reduces CPU overhead and latency. It allows smoother execution even during high-load diagnostic sessions. This is a major advantage in real-time automotive systems.
5. Improves Diagnostic Flexibility: The service isn’t just limited to firmware updates it can be used for calibration, logging, or configuration changes. This versatility makes it useful in multiple diagnostic scenarios. Engineers can dynamically load different types of data based on system requirements. It adds flexibility to diagnostic workflows. Such adaptability reduces the need for custom solutions.
6. Enhances Security and Access Control: The Transfer Data service works with UDS security levels, so memory access can be restricted to authorized clients. It requires prior security unlocking using SecurityAccess (0x27). This ensures that sensitive data cannot be altered by unauthorized tools. It adds an essential layer of protection to the ECU. This is critical in modern connected vehicles.
7. Reduces Reprogramming Time: By using optimized block sizes and high-speed communication, Transfer Data speeds up the data writing process. This is important in large software updates where time is a factor. Reduced flashing time means less downtime in production or service centers. It also improves the user experience in over-the-air (OTA) updates. Faster updates mean greater operational efficiency.
8. Scalable Across ECU Platforms: As part of the standardized UDS protocol (ISO 14229), this service is widely supported across multiple OEMs and ECU suppliers. It allows reuse of code and workflows across various projects. This standardization simplifies development and testing. Developers can apply common tools and scripts across platforms. It promotes interoperability in multi-ECU environments.
9. Error Handling and Recovery: The service includes error detection and response mechanisms, so if a block fails, only that block needs to be re-sent. This avoids restarting the entire session. The ECU provides negative responses when something goes wrong, helping in troubleshooting. This robust error handling ensures data accuracy. It also prevents incomplete or broken updates.
10. Supports Integration with Other UDS Services: Transfer Data is typically used with services like Request Download (0x34) and Transfer Exit (0x37) to create a complete data transfer session. These services work in harmony to manage session state and memory allocation. The entire process becomes more streamlined and manageable. It helps engineers structure the programming cycle clearly. This integration ensures consistency and reliability.

Disadvantages of Transfer Data (0x36) Service in UDS Protocol

Following are the Disadvantages of Transfer Data (0x36) Service in UDS Protocol:

1. Requires Complex Session Management: Transfer Data must be used in an active diagnostic session, often requiring transitions to programming session and proper sequence with Request Download and Transfer Exit. Managing session timeouts, security unlocking, and service sequencing can become complex for developers. Errors in session handling may lead to incomplete or failed updates. This increases implementation effort and the chance for mistakes. Careful timing and control are necessary to ensure success.
2. Sensitive to Data Packet Loss: Since data is sent in blocks, any loss or corruption of a packet can disrupt the entire transfer process. Even a single missing block can lead to session failure if not handled properly. Recovery mechanisms like retransmissions need to be built into the system. This dependency on network reliability makes the service vulnerable in noisy or unstable environments. Extra validation adds processing overhead.
3. Security Risk if Not Protected: If Transfer Data is not properly secured using the UDS Security Access service, it may expose the ECU to unauthorized data injection or memory corruption. Attackers could potentially overwrite critical memory sections. Therefore, security measures must be strictly enforced. This adds extra steps and complexity to every session. Neglecting it can lead to serious system vulnerabilities.
4. High Dependency on Accurate Block Counters: The block counter must increment correctly for each data packet. If the sequence is broken due to transmission errors or software bugs, the ECU may reject the block. A mismatch in counters will require the session to reset or recover. This adds to error handling requirements in the client and server. Managing counters accurately across the session is crucial but often error-prone.
5. Limited by ECU Memory Handling Capabilities: Some ECUs may have restrictions on where and how much data can be written using Transfer Data. This can limit the scope of reprogramming or updates. If memory management is not optimized, larger updates can fail or require special handling. The client needs to align exactly with the ECU’s memory structure. This can make integration with legacy systems difficult.
6. Lack of Standard Retry Logic: Unlike higher-level protocols, Transfer Data does not define automatic retry mechanisms for failed blocks. This responsibility falls entirely on the application layer of the client. Implementing custom retry logic increases development time and testing complexity. If not properly handled, failed sessions may require a full restart. It increases the load on both the client and ECU.
7. Complex Diagnostic Tool Implementation: Creating a tool that manages Transfer Data sessions correctly requires attention to many parameters, including timing, block size, counters, and security. Implementing this in diagnostic tools or scripting environments can be time-consuming. Any mistake in handling may lead to memory corruption or bricked ECUs. This demands experienced developers and extensive validation efforts.
8. Not Suitable for Real-Time Applications: The service is designed for offline or programming activities and not meant for real-time systems. Using it during live operations or active driving could cause system instability. It is not optimized for performance-critical environments. Data transfer may temporarily halt other ECU tasks. Therefore, its use is limited to maintenance or controlled conditions.
9. Potential for Bricking if Interrupted: If the session is interrupted (due to power failure, connection loss, etc.) during a critical phase, it can leave the ECU in an unusable state. Recovery may require special bootloaders or hardware-level reprogramming. This is especially dangerous during firmware upgrades. Extra safety measures must be taken, increasing complexity and cost.
10. Requires Coordination with OEM Protocol Stack: The way Transfer Data is implemented can vary slightly between different OEMs or Tier-1 suppliers. This makes it difficult to create one universal solution. Developers need to adapt their implementation based on OEM-specific configurations and memory maps. This reduces portability and increases integration challenges. It also requires thorough documentation and cooperation with vendors.

Future Development and Enhancement of Transfer Data (0x36) Service in UDS Protocol

Here are the Future Development and Enhancement of Transfer Data (0x36) Service in UDS Protocol:

1. Improved Data Integrity Checks: Future UDS implementations may enhance integrity checks by introducing stronger checksum algorithms or error-correcting codes. This will ensure that the data being transferred is not only intact but also automatically corrected in case of minor bit errors, increasing the reliability of ECU flashing processes.
2. Dynamic Block Size Adjustment: Upcoming updates could support adaptive block sizes based on available bandwidth and ECU performance. This would allow smoother transfers over both high-speed and low-speed networks by automatically optimizing the data chunks, improving throughput and reducing communication errors.
3. Integration with OTA Update Systems: With over-the-air updates becoming standard, the Transfer Data service may evolve to support OTA-specific protocols and wireless error management. This ensures safe and reliable firmware or calibration updates without requiring physical access to the vehicle, making remote diagnostics and updates easier.
4. Secure Session Management: Future enhancements are expected to include robust session management features, such as encrypted handshakes and authenticated sessions. These additions will protect against unauthorized access during data transfers and ensure that only verified users or tools can initiate sensitive memory operations.
5. Parallel Transfer Channels: Next-gen ECUs might support multiple Transfer Data sessions running in parallel. This would allow faster and more efficient reprogramming of different ECU regions at once, which is particularly useful in modern multi-core or domain-based automotive architectures.
6. Improved Transfer Error Feedback: Enhancements could include more detailed negative response codes and error logging within the Transfer Data session. These improvements would make it easier for developers to debug failed transfers, reducing downtime and simplifying troubleshooting during diagnostics.
7. Support for Flash Memory Optimization: Future standards may allow the Transfer Data service to detect and skip already-matching memory blocks, reducing unnecessary flash writes. This optimization conserves memory lifespan and significantly accelerates the programming process, especially for minor software updates.
8. Cloud-Based Transfer Management: The Transfer Data process may be integrated with cloud-based tools that allow real-time monitoring, scheduling, and verification of reprogramming tasks. Cloud connectivity could also help in maintaining version control and storing audit logs for safety and compliance.
9. AI-Powered Transfer Prediction: Machine learning algorithms might be used to predict the best time or method to perform data transfers based on past vehicle diagnostics and network health. This predictive intelligence can help prevent failures and schedule updates at optimal times, improving success rates.
10. Cross-Platform ECU Compatibility: Future updates may standardize the Transfer Data behavior across different ECU vendors and chipsets. This universal behavior will simplify tool development, reduce customization efforts, and improve interoperability between OEM tools and third-party diagnostic equipment.