Complete Guide to Request Transfer Exit (0x37) UDS Service for Automotive Applications

Hello, automotive diagnostics enthusiasts! In this blog post, I will introduce you to UDS Protocol Request Transfer Exit (0x37) Service – one of the final and essential services

in the UDS protocol: the Request Transfer Exit (0x37) service. This service plays a critical role in concluding data transfer operations during ECU flashing and memory programming. It signals the end of a successful data transfer session between a diagnostic tester and an ECU. Whether you’re working on software reprogramming, data integrity checks, or secure diagnostics, understanding this service is crucial. I will explain what 0x37 does, how it fits into the diagnostic workflow, and its importance in ensuring seamless and validated data transfers. By the end of this post, you’ll have a clear understanding of how to implement and use the Request Transfer Exit service in real-world automotive scenarios. Let’s explore the final handshake of the UDS data transfer process!

Introduction to Request Transfer Exit (0x37) Service in UDS Protocol

Welcome to another exciting exploration of UDS protocol services! In this post, we’ll dive into the Request Transfer Exit (0x37) service an essential step in concluding the data transfer process during ECU programming. This service acts as a formal signal to the ECU that all data has been successfully sent, and it can now proceed with internal processing, such as verification or flashing. Without this step, data transfer sessions remain incomplete, risking memory corruption or failed updates. We’ll cover its purpose, message format, and how it fits into the broader UDS sequence. Whether you’re developing diagnostics tools or performing firmware updates, understanding 0x37 is key. Let’s unlock the final phase of secure data handling in automotive ECUs!

What is Request Transfer Exit (0x37) Service in UDS Protocol?

The Request Transfer Exit (0x37) service in the UDS (Unified Diagnostic Services) protocol is used to signal the end of a data transfer session, typically following a sequence of data blocks sent using the Transfer Data (0x36) service. When a diagnostic client finishes sending all the required data to the ECU (Electronic Control Unit), it uses this service to notify the ECU that no further data will be transmitted and that the ECU should now validate or apply the received data. This service is critical during operations like ECU reprogramming, firmware flashing, or calibration, ensuring a clean and structured conclusion to the data upload process. The 0x37 service may also include optional parameters, such as checksums or status flags, to help the ECU validate the integrity of the transmission.

Note: This service does not use a sub-function

Why do we need Request Transfer Exit (0x37) Service in UDS Protocol?

Here are the key reasons why the Request Transfer Exit (0x37) service is needed in the UDS protocol:

1. Proper Termination of Data Transfer

The Request Transfer Exit service is essential to indicate the successful completion of the data transfer process. After multiple data blocks are sent using the Transfer Data (0x36) service, the ECU waits for a final command to confirm the end. Without this confirmation, the ECU might continue to wait or treat the session as incomplete. This can lead to inconsistencies or system faults. The 0x37 service ensures a clean and well-defined end point. It wraps up the transfer sequence and prepares the ECU for validation.

2. Trigger for Data Validation Process

Once the transfer phase ends, the ECU needs to verify whether all the received data is accurate and complete. The Request Transfer Exit (0x37) acts as a trigger for this data validation step. It informs the ECU that no more data will be received, so it can now perform checksum verification or signature checks. This is critical to ensure firmware integrity before applying changes. It reduces the risk of applying corrupted or partial firmware. It also improves the reliability of the update process.

3. Checksum or Final Data Confirmation

The 0x37 service can carry optional parameters like a checksum or CRC. These values allow the ECU to compare its locally calculated checksum with the value sent by the client. This ensures that the data received matches the intended content sent during Transfer Data. It’s a key element in validating memory integrity before flashing. This mechanism strengthens trust in the data and prevents silent errors. It enhances diagnostic safety, especially in critical systems.

4. Avoid Incomplete Programming States

Without a proper transfer exit, the ECU may remain in an ambiguous state where it is unsure if the programming is finished. This can lead to incomplete memory updates, crashes, or failures during ECU reboot. The 0x37 service ensures that the ECU understands the end of the programming operation. It prevents the application of partial or invalid data. This is crucial in safety-critical automotive systems. It helps maintain the system’s stability and reliability.

5. Support for Session Control Logic

The Request Transfer Exit service supports smooth transitions between different diagnostic sessions like programming and extended sessions. It helps the ECU maintain logical boundaries between stages of communication. After receiving this request, the ECU can prepare for the next step, like exiting the programming mode or rebooting. It supports structured and modular ECU behavior. It makes the diagnostic session predictable and manageable for both client and ECU.

6. Improves Reusability in Toolchains

Standardized termination of data transfer using 0x37 makes tool development easier. Diagnostic tools can reuse the same logic across multiple ECUs when the communication sequence is consistent. This reduces development time and increases reliability. It also ensures compatibility with OEM flashing standards. By having a fixed exit point, script automation becomes more efficient. It enhances the scalability of diagnostic systems.

7. Enhanced Security Handling

The 0x37 service is often integrated into secure programming workflows. It can serve as a final step where the ECU checks security tokens or cryptographic conditions. This prevents unauthorized users from triggering firmware activation. It helps enforce access control at a critical point in the process. Secure handling of the transfer exit also minimizes risks related to tampering or misuse. It’s an important part of trusted boot and secure diagnostics.

8. Ensures Synchronization Between Client and ECU

During data transfer, it’s important that both the client and the ECU stay in sync. The 0x37 service acts as a common handshake, confirming that both sides have reached the same point. It helps avoid miscommunication or timeout errors. It ensures that the ECU does not misinterpret incoming messages. This synchronization improves system robustness and reduces the likelihood of programming failures. It maintains order in multi-block transfers.

9. Minimizes the Risk of Data Loss

By signaling the end of the transfer, the 0x37 service ensures the ECU doesn’t accidentally ignore or overwrite important data. It defines a boundary between accepted and unprocessed data. This clarity prevents accidental memory writes beyond expected areas. It is particularly useful in large firmware or parameter datasets. The service minimizes the risk of data corruption or application crashes. It improves the efficiency of memory management.

10. Facilitates Error Detection and Handling

The 0x37 service provides a feedback mechanism. If there’s a problem with the previous data blocks, the ECU can reject the transfer and send back a negative response. This allows the client to detect and address errors before continuing. It also enables diagnostic tools to provide user-friendly error messages. This proactive detection prevents further problems. It makes the flashing and programming process safer and more reliable.

Syntax of 0x37 SID Request Message Frame Format

Data byte	Parameter Name	Byte Value
#1	Request Transfer Exit Request SID	0x37
#2 : #n	Transfer Request Parameter Record[] = [                                 transfer Request Parameter#1                                                      :                                 transfer Request Parameter#m ]	0x00 – 0xFF : 0x00 – 0xFF

Request Message Data-Parameter

TransferRequestParameterRecord

This parameter record contains data needed by the server to support the transfer of data. The format and length are vehicle manufacturer specific.

Syntax of 0x37 SID Positive Response Message Frame Format

Data byte	Parameter Name	Byte Value
#1	Request Transfer Exit +Ve Response SID	0x77
#2 : #n	Transfer Response Parameter Record[] = [                transfer Response Parameter#1                                                      :                             transfer Response Parameter#m ]	0x00 – 0xFF : 0x00 – 0xFF

Response Message Data-Parameter

TransferResponseParameterRecord

This parameter contains data needed by the client to support the transfer of data. The format and length are vehicle manufacturer specific.

Syntax of 0x37 SID Negative Response Message Frame Format

Data byte	Parameter Name	Byte Value
#1	Request Transfer Exit –Ve Response SID [byte#1]	0x7F
#2	Requested SID [byte#1]	0x37
#3	Negative Response Code [byte#1]	NRC

Supported Negative Response Codes (NRCs) for 0x37 SID in UDS Protocol

NRC	Parameter Name	Description
0x13	Incorrect Message Length Or Invalid Format	This NRC will be returned if the message length is incorrect.
0x24	Request Sequence Error	This NRC shall be returned if: • The programming process is not completed when a request for this service is received; • The Request Download or Request Upload service is not active;
0x31	Request Out Of Range	This NRC will be returned if the transfer Request Parameter Record contains invalid data.
0x72	General Programming Failure	This NRC will be returned if the server encounters an error while finalizing the data transfer between the client and server (e.g., due to an integrity check failure).

Example of Request Transfer Exit (0x37) Service in UDS Protocol

These are the Examples of Request Transfer Exit (0x37) Service in UDS Protocol:

Step #1: Request for Download (0x34)

Request Download Request Message Flow Example:

Message direction	Client → Server
Message Type	Request
Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Request Download Request SID	0x34
#2	Data Format Identifier	0x11
#3	Address And Length Format Identifier	0x33
#4 #5 #6	Memory Address [ byte#1 ] (MSB) Memory Address [ byte#2 ]  Memory Address [ byte#3 ] (LSB)	0x60 0x20 0x00
#7 #8 #9	Memory Size [ byte#1 ] (MSB) Memory Size [ byte#2 ] Memory Size [ byte#3 ] (LSB)	0x00 0xFF 0xFF

Request Download Positive Response Message Flow Example:

Message direction	Server → Client
Message Type	Response
Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Request Download +Ve Response SID	0x74
#2	Length Format Identifier	0x20
#3 #4	Max Number Of Block Length [ byte#1 ] (MSB) Max Number Of Block Length [ byte#2 ] (LSB)	0x00 0x81

Request Download Negative Response Message Flow Example:

Message direction	Server → Client
Message Type	Response
Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Request Download –Ve Response SID [ byte#1 ]	0x7F
#2	Requested SID [ byte#1 ]	0x34
#3	Negative Response Code [ byte#1 ]	NRC

Step #2: Transfer Data (0x36)

Transfer Data Request Message Flow Example:

Message direction	Client → Server
Message Type	Request
Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Transfer Data Request SID	0x36
#2	Block Sequence Counter	0x01
#3 : #129	Transfer Request Parameter Record [                                   transfer Request Parameter#1 ] = data Byte#3 : Transfer Request Parameter Record [                transfer Request Parameter#127 ] = dataByte#129	0xXX : 0xXX

Transfer Data Positive Response Message Flow Example:

Message direction	Server → Client
Message Type	Response
Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Transfer Data +Ve Response SID	0x76
#2	Block Sequence Counter	0x01

Transfer Data Negative Response Message Flow Example:

Message direction	Server → Client
Message Type	Response
Data byte	Description (all values are in hexadecimal)	Byte Value
#1	Transfer Data –Ve Response SID [ byte#1 ]	0x7F
#2	Requested SID [ byte#1 ]	0x36
#3	Negative Response Code [ byte#1 ]	NRC

Example of Request Transfer Exit (0x37) SID

Example of Request Frame Format:

PCI Length	SID	Transfer Request Parameter Record
0x03	0x37	0x01	0x30

Example of Positive Response:

PCI Length	Response SID	Block Sequence Counter
0x02	0x77	0x04

Example of Request Frame Format:

PCI Length	SID	Transfer Request Parameter Record
0x05	0x37	0x01	0x30

Example of Negative Response:

PCI Length	Response SID	Request SID	NRC
0x03	0x7F	0x37	0x13

Advantages of Request Transfer Exit (0x37) Service in UDS Protocol

Following are the Advantages of Request Transfer Exit (0x37) Service in UDS Protocol:

1. Ensures Clean Termination of Data Transfer: The 0x37 service cleanly ends the data transfer process, signaling to the ECU that no further data will be sent, preventing ambiguity. This allows the ECU to finalize the memory write and transition to the next step without expecting additional data. By ensuring a clear termination, it prevents incomplete data transfers, ensuring the stability and reliability of ECU reprogramming sessions.
2. Enables Post-Transfer Validation: Once the 0x37 request is sent, the ECU performs checks like checksums or signature verification to validate the integrity of the transferred data. This step ensures that the data written into the ECU’s memory is correct and uncorrupted, reducing the risk of errors during reprogramming. Validation is critical to guarantee the safe execution of firmware or configuration changes.
3. Improves Communication Synchronization: The 0x37 service acts as a synchronization signal that both the diagnostic tool and the ECU recognize, ensuring they are aligned on the transfer status. This synchronization eliminates the risk of mismatches and ensures that both parties are aware that the data transfer has been completed, which helps in maintaining a smooth communication process and reducing errors in diagnostic sessions.
4. Supports Secure Programming Workflow: In secure programming scenarios, the 0x37 service is crucial for triggering the final authentication or security checks before committing changes. This step prevents unauthorized or erroneous data from being written to the ECU, which is especially important for protecting intellectual property and ensuring the vehicle’s security against potential threats or hacks during updates.
5. Improves Toolchain Compatibility: By using the standardized 0x37 service, diagnostic and flashing tools can be designed to work seamlessly across multiple ECUs and platforms. This reduces the need for custom logic in each ECU programming tool and streamlines the development of diagnostic tools. It allows manufacturers and developers to use a unified approach to ECU programming, improving the consistency and efficiency of the process.
6. Enables Clear Error Feedback: If an issue arises during the data transfer, the ECU can use the 0x37 service to provide feedback, signaling whether the transfer was successful or if an error occurred. This clear error feedback allows the diagnostic tool to take corrective actions or abort the process as necessary, improving the reliability of the reprogramming process and minimizing the chances of a failed ECU update.
7. Supports Efficient Flashing Operations: The 0x37 service helps optimize the flashing process by ensuring that the system doesn’t get stuck in an incomplete or incorrect state. It signals the successful completion of a transfer, allowing the ECU to finalize its operations and proceed with the next step. This efficiency is crucial for reducing downtime during ECU reprogramming and improving the overall user experience during maintenance or repairs.
8. Minimizes Data Loss Risks: The 0x37 service minimizes the risk of data loss during the reprogramming process. By signaling the end of the data transfer session, it ensures that all data blocks are successfully written to memory before any changes are finalized. This reduces the chances of incomplete data or memory corruption, which can lead to system malfunctions or unreliable vehicle behavior.
9. Streamlines Firmware Update Process: The use of 0x37 in the UDS protocol makes the process of updating ECU firmware more streamlined and predictable. It provides a clear point of termination for the data transfer phase, simplifying the update process. By signaling the end of data upload, it ensures that the firmware update can be committed with confidence, reducing complexity and manual intervention in diagnostic procedures.
10. Enhances Diagnostic Session Management: The 0x37 service helps improve overall session management by providing a clear transition point between different stages of ECU programming. It marks the end of the data transfer phase, making it easier to manage subsequent tasks such as system initialization or error handling. This enhances the overall workflow, ensuring that all diagnostic and reprogramming tasks are carried out efficiently and in a well-organized manner.

Disadvantages of Request Transfer Exit (0x37) Service in UDS Protocol

Following are the Disadvantages of Request Transfer Exit (0x37) Service in UDS Protocol:

1. Limited Flexibility for Large Transfers: The 0x37 service is designed to terminate the transfer session once all data is uploaded, which may cause issues in cases where the transfer is incomplete or needs to be split into multiple sessions. This lack of flexibility can cause delays or interruptions in systems where large amounts of data are being transferred, as the session cannot easily be paused or resumed.
2. Potential for Miscommunication: If the diagnostic tool or ECU misinterprets the 0x37 signal, it can lead to synchronization problems. For instance, the ECU may consider the session complete even though the tool hasn’t finished sending all the data. This miscommunication can result in incomplete or erroneous data uploads, which might lead to ECU malfunction or the need to repeat the transfer process.
3. Dependency on Proper Error Handling: If the error handling mechanisms are not well-implemented, the 0x37 service may not correctly address or report issues during the transfer. This could leave the system in an unstable state, especially if the request to exit the transfer session occurs prematurely or without proper checks, potentially causing a failure in the ECU reprogramming or diagnostic process.
4. Overhead in Smaller Systems: In smaller, more efficient ECU programming systems, the additional overhead introduced by the 0x37 service might seem unnecessary. The added complexity of sending and verifying a transfer exit request could increase the time required for reprogramming and diagnostics in low-resource systems, where simplicity and speed are prioritized.
5. Unwanted Data Deletion Risks: If the 0x37 service is triggered prematurely, there is a risk that data may be written over or erased before the transfer is fully completed. This could result in the loss of valuable data or corrupt firmware, especially in the case of partial or aborted updates. Inadequate system safeguards could exacerbate this risk, leading to issues during reprogramming or diagnostic sessions.
6. Complex Session Management: The 0x37 service introduces complexity when managing multi-step data transfers. If data needs to be transferred in chunks over multiple sessions, the request to exit the transfer (0x37) may require careful session management, especially when certain data blocks need to be validated before completing the session. Managing these nuances adds complexity to the overall process, requiring developers to build additional logic for proper handling.
7. Potential for Delays: In cases where multiple data chunks are transferred, invoking the 0x37 service too early can cause delays in the reprogramming process. This can be particularly problematic when time-sensitive ECU updates are required, such as in manufacturing environments or during vehicle diagnostics, where efficiency and time management are crucial for system maintenance.
8. Increased Debugging Effort: When issues occur during the data transfer process, the 0x37 service can make troubleshooting more challenging. Developers and engineers may need to analyze the session history and transfer logs in detail to identify if the premature termination or errors in the transfer process are due to the request to exit the transfer session. This added debugging complexity increases development time and maintenance efforts.
9. Compatibility Issues with Non-Standard ECUs: Some ECUs may not fully support the 0x37 service or may have unique handling mechanisms for transfer exits. These compatibility issues can result in errors or unexpected behavior when trying to implement the 0x37 service on different ECU platforms, creating challenges in ensuring that the service works universally across a wide range of vehicles or systems.
10. Security Concerns: If the transfer session is prematurely closed without ensuring all security checks are completed, there is a risk that the ECU might be left vulnerable. Insecure or incomplete updates could expose the vehicle to unauthorized access or firmware corruption, leading to potential cybersecurity risks, especially if the update involves sensitive vehicle functionalities like anti-theft systems or communication protocols.

Future Development and Enhancement of Request Transfer Exit (0x37) Service in UDS Protocol

Here are the Future Developments and Enhancements of Request Transfer Exit (0x37) Service in UDS Protocol:

1. Improved Error Handling Mechanisms: Future versions of the 0x37 service could incorporate more advanced error detection and handling protocols. This would enable the service to provide more specific feedback in case of transfer issues, such as incomplete data or unexpected interruptions. Enhanced error handling would help developers quickly diagnose and resolve issues, reducing the likelihood of malfunction during ECU reprogramming or diagnostics.
2. Support for Incremental Transfers: One potential enhancement could be the ability to support incremental data transfers within the 0x37 service. Currently, once the service is triggered, it ends the transfer session. Future updates might allow for incremental or partial data uploads, where the transfer session can continue after a pause or be resumed, offering more flexibility and reducing the risk of data loss.
3. Optimized Session Management: Improved session management techniques could be implemented in future versions, allowing the 0x37 service to handle more complex data flows. This could include handling multi-step data transfers and better tracking of data blocks, making the process smoother, faster, and more efficient, especially in systems that require frequent data updates or reprogramming.
4. Integration with Advanced Security Features: As vehicle security becomes more important, the future development of the 0x37 service could include integration with advanced encryption and authentication mechanisms. These security features would ensure that only authorized users can initiate the transfer exit and that no malicious modifications can be made during the data transfer or when closing the session.
5. Support for Larger Data Volumes: Future versions of the 0x37 service could be designed to handle larger data volumes more efficiently. This would be particularly useful for high-performance ECUs that manage complex systems, such as autonomous driving or electric vehicle management systems. The ability to transfer large data sets without compromising speed or stability would be a key improvement for these high-end applications.
6. Improved Multi-ECU Coordination: In scenarios where multiple ECUs are involved, future updates to the 0x37 service could improve its coordination capabilities. This would allow for more synchronized transfer sessions, enabling smoother communication between different ECUs. Enhancing multi-ECU support would be vital for systems where various components need to be updated simultaneously, such as in the case of complex automotive networks.
7. Customization for OEMs and Manufacturers: Automakers and ECU manufacturers may want to customize the 0x37 service to suit their specific needs. Future developments could offer OEMs more flexibility in defining how the service is implemented, including custom timeouts, response formats, and error handling protocols. This would provide manufacturers with a tailored experience for ECU reprogramming and diagnostics.
8. Extended Diagnostic Data Support: Future versions of the 0x37 service could extend support to handle not only firmware and software updates but also diagnostic data uploads. This would allow for a more unified approach to vehicle maintenance, where diagnostic information and software reprogramming can be managed within the same session, improving the efficiency of repair and diagnostic processes.
9. Faster Data Transmission Rates: As automotive systems become more data-intensive, there will be a demand for faster data transmission rates. Future iterations of the 0x37 service could include optimizations for speed, enabling quicker closure of transfer sessions and more efficient communication between the ECU and diagnostic tools. This would be particularly beneficial in time-sensitive scenarios such as manufacturing or roadside diagnostics.
10. Enhanced Compatibility with Future Automotive Protocols: As new communication protocols emerge in the automotive industry, the 0x37 service will likely need to evolve to ensure compatibility with these protocols. Future developments could make the service more adaptable to future technologies, such as V2X (Vehicle-to-Everything) communications, autonomous vehicle systems, or IoT-enabled vehicle platforms, ensuring its relevance as the industry advances.