UDS 0x19 Service: How Report DTC Snapshot Identification (0x03) Works

Hello, fellow automotive tech enthusiasts! In this blog post, I’ll introduce you to Report DTC Snapshot Identification 0x03 UDS – one of the key diagnost

ic functions in the UDS (Unified Diagnostic Services) protocol – the Report DTC Snapshot Identification sub-function (0x03) of the 0x19 service. This sub-function is essential for retrieving detailed snapshots of diagnostic trouble codes (DTCs), which help in understanding vehicle faults. Snapshots offer valuable context by capturing the vehicle’s internal data at the time a DTC was triggered. This feature is widely used in ECU diagnostics, testing, and debugging. In this post, I’ll explain how 0x03 works, how the request and response messages are structured, and provide practical examples for better clarity. By the end, you’ll have a clear grasp of how to implement and interpret this sub-function. Let’s dive into UDS diagnostics!

Introduction to 0x03 – Report DTC Snapshot Identification in UDS 0x19 Service

Hello, diagnostic enthusiasts! In this article, we’ll explore an essential part of the UDS (Unified Diagnostic Services) protocol – the Report DTC Snapshot Identification sub-function (0x03) of the 0x19 service. This service allows you to retrieve detailed freeze frame data related to specific Diagnostic Trouble Codes (DTCs). These snapshots capture real-time vehicle parameters at the moment a fault occurs, making them crucial for analyzing and diagnosing issues. Understanding how this sub-function works is vital for ECU developers, testers, and automotive engineers. We’ll cover how the request/response format looks, its parameters, and how it fits into the overall diagnostic process. By the end of this post, you’ll have a clear view of how to work with snapshot data using UDS. Let’s get started!

What is 0x03 Report DTC Snapshot Identification in UDS 0x19 Service?

The Unified Diagnostic Services (UDS) protocol is a diagnostic communication protocol used primarily in the automotive industry to communicate with various electronic control units (ECUs) in a vehicle. It’s part of the ISO 14229 standard, which is widely adopted for diagnostic and service-related tasks in modern vehicles. The 0x19 Service (also called “Read DTC Information”) is a key diagnostic service within the UDS protocol that allows a diagnostic tool (such as a scan tool or ECU tester) to read information about Diagnostic Trouble Codes (DTCs) stored in the vehicle’s ECUs. These DTCs help technicians identify issues or faults within the vehicle.

The 0x03 sub-function of the 0x19 Service is known as “Report DTC Snapshot Identification”. It plays a crucial role in retrieving additional context or snapshot data associated with specific DTCs. A snapshot is essentially a snapshot of the vehicle’s data at the time a fault (represented by a DTC) was detected. This snapshot data includes important vehicle parameters (such as engine speed, temperature, or voltage), which can help technicians understand the conditions under which a fault occurred. By providing this real-time data, the snapshot allows for a more thorough and accurate diagnosis.

Why do we need 0x03 Report DTC Snapshot Identification in UDS 0x19 Service?

The 0x03 Report DTC Snapshot Identification sub-function in the UDS 0x19 Service plays a critical role in modern automotive diagnostics. Here’s why it’s indispensable:

1. Provides Context for Diagnostic Trouble Codes (DTCs)

Simply retrieving a Diagnostic Trouble Code (DTC) doesn’t give enough insight into what was happening in the vehicle when the fault occurred. A DTC only points to a specific issue, but it doesn’t provide any contextual information about the state of the vehicle at the time of the fault.

The 0x03 Report DTC Snapshot Identification sub-function helps address this gap by capturing a snapshot of key vehicle parameters at the exact moment a fault was detected. These parameters can include engine speed, throttle position, fuel pressure, and many others. Without this context, diagnosing the root cause of a problem would be much harder.

2. Freeze-Frame Data for Intermittent Issues

Some faults are intermittent, meaning they don’t always occur under the same conditions, making them difficult to diagnose. For example, an engine misfire may only occur at a certain RPM or temperature. If a technician only has access to the DTC without knowing the exact vehicle conditions, they may struggle to reproduce or pinpoint the issue.

By using the 0x03 sub-function, the snapshot data freezes key parameters at the time the DTC is triggered, providing invaluable information about the conditions under which the issue occurred. This freeze-frame data helps capture fleeting issues that could be easily missed during normal operation.

3. Enhanced Troubleshooting and Faster Diagnosis

With the snapshot data, technicians can make much faster and more accurate diagnoses. Instead of guessing or manually testing various systems, they can use the snapshot data to:

• Pinpoint whether the problem was related to fuel delivery, sensor malfunction, or electrical issues.
• Identify patterns in the data, helping them understand if certain conditions (like high temperature or low fuel pressure) contribute to recurring faults.

This level of detailed diagnostics accelerates troubleshooting, reducing downtime and improving repair turnaround times.

4. Improves Vehicle System Testing and Calibration

For engineers developing or testing new ECUs (Electronic Control Units), having access to 0x03 Report DTC Snapshot Identification is essential. It allows them to:

• Test system behavior under various conditions.
• Ensure accuracy of sensor readings and ECU responses to faults.
• Refine system calibration, ensuring that the vehicle’s systems react appropriately when faults occur, leading to more reliable and optimized performance.

Snapshot data helps fine-tune systems by giving engineers a real-time view of the vehicle’s operational state when faults are triggered.

5. Critical for ECU Development and Validation

When working with ECUs during development, engineers and developers rely heavily on detailed data to verify that the systems are functioning as expected. If an ECU triggers a fault, 0x03 Report DTC Snapshot Identification provides the precise data needed to:

• Validate that the ECU is reading and responding to sensor inputs correctly.
• Identify issues in real-time, making it easier to debug and resolve problems before the vehicle is released to the market.

Without this data, engineers would be left to perform manual troubleshooting, which is much more time-consuming and error-prone.

6. Supports Advanced Diagnostic Tools

Modern diagnostic tools and scan tools can utilize the 0x03 sub-function to provide advanced diagnostics that go beyond just reading DTCs. These tools can:

• Graph vehicle parameters at the time the DTC was triggered.
• Generate reports that display the data in a way that’s easy for technicians to interpret.
• Offer proactive diagnostics, allowing for predictive maintenance before a fault turns into a serious issue.

The snapshot data enhances the functionality of diagnostic equipment, allowing it to provide better insights and facilitating predictive vehicle maintenance.

7. Reduces Repair Costs and Increases Reliability

With the ability to view the snapshot data, mechanics and technicians can make more accurate repairs the first time around, reducing the need for:

• Trial and error repairs.
• Multiple trips to the shop for the same issue.
• Costly downtime for vehicle owners or fleet operators.

This not only leads to reduced repair costs but also improves vehicle reliability by ensuring that faults are fixed correctly the first time, preventing recurring issues.

Report DTC Snapshot Identification SBFID (0x03) of SID (0x19)

• A client can retrieve DTCSnapshot record identification information for all stored snapshots by sending a request with the sub-function reportDTCSnapshotIdentification.
• The server will return a list of DTCSnapshot records, each containing a DTC number (high, middle, and low byte) and a unique DTCSnapshot record number.
• If multiple snapshots are stored for a single DTC, each occurrence will be listed with a different record number.

Note: A server may store multiple snapshots for a single DTC to track conditions at each occurrence.

• The system supplier or vehicle manufacturer defines how many snapshots are stored, as well as the criteria for defining an “occurrence.”
• DTCSnapshot records are cleared with a successful ClearDiagnosticInformation request, and the vehicle manufacturer determines the rules for deleting DTCs and snapshots in case of memory overflow.

What is DTC Snapshot Identification?

DTC Snapshot Identification refers to the process of capturing and identifying a snapshot of specific conditions or data points when a Diagnostic Trouble Code (DTC) is set. In automotive diagnostics, when a fault is detected and a DTC is generated, the system may also capture a “snapshot” of relevant vehicle parameters at the time the fault occurred. This snapshot can include information such as engine speed, vehicle speed, sensor readings, and other operational data.

Key Points about DTC Snapshot Identification:

1. Snapshot Records: When a fault occurs, the system stores a snapshot record that captures the conditions under which the fault happened. This record is linked to the specific DTC.
2. Identification Information: Each snapshot is assigned a unique identifier, which includes the DTC number and a snapshot record number. This identification information allows technicians to retrieve and analyze the exact conditions present when the fault was detected.
3. Multiple Snapshots: If the same DTC occurs multiple times, the system may store multiple snapshot records, each with a different record number, to track the conditions of each occurrence.
4. Usage: The snapshot identification information is useful for troubleshooting, as it provides a detailed context for the fault, helping technicians understand the circumstances leading to the issue.
5. Clearing Snapshots: Snapshots are cleared from the system when the ClearDiagnosticInformation request is successfully processed.
   • DTC Snapshot Identification is a mechanism to track and retrieve detailed information about the conditions under which a DTC was triggered, aiding in the diagnosis and repair of vehicle faults.

Mandatory Snapshot Records

There are so many Snapshot data records can be added by the OEM or any suppliers. But still there are some data records that should be the mandatory as per the ISO standards, such as:

• Outdoor Temperature(P1AFR)
• Odometer(P1AFS)
• Vehicle mode(P1AFT)

Syntax of Report DTC Snapshot Identification (SBFID-0x03) of SID-0x19

Request Message Definition – Sub-Function = Report DTC Snapshot Identification

Data byte	Parameter Name	Byte Value
#1	Read DTC Information Request SID	0x19
#2	sub-function = [ report Type =             report DTC Snapshot Identification ]	0x03
#3 #4 #5	DTC Mask Record[] = [                                        DTC High Byte                                        DTC Middle Byte                                        DTC Low Byte ]	0x00 – 0xFF 0x00 – 0xFF 0x00 – 0xFF
#6	DTC Snap shot Record Number	0x00 – 0xFF
C: The presence of the DTC Mask Record record and the DTC Snapshot Record Number parameter is conditional upon the sub-function parameter being set to report DTC Snapshot Record By DTC Number.

SBFID (0x03) Request Message Data-Parameter of SID (0x19)

reportType: This parameter reflects bits 6 – 0 of the sub-function parameter from the client’s request message.

DTCMaskRecord [DTCHighByte, DTCMiddleByte, DTCLowByte]

DTCMaskRecord is a 3-byte value representing a unique diagnostic trouble code (DTC) using DTCHighByte, DTCMiddleByte, and DTCLowByte. The DTC can be decoded in various ways:

• ISO 15031-6: Identified by DTCFormatIdentifier = SAE_J2012-DA_DTCFormat_00
• ISO 14229: Identified by DTCFormatIdentifier = ISO_14229-1_DTCFormat (manufacturer-defined)
• SAE J1939-73: Identified by DTCFormatIdentifier = SAE_J1939-73_DTCFormat
• ISO 11992-4: Identified by DTCFormatIdentifier = ISO_11992-4_DTCFormat
• ISO 27145-2: Identified by DTCFormatIdentifier = SAE_J2012-DA_WWH-OBD_DTCFormat

DTCSnapshotRecordNumber

DTCSnapshotRecordNumber is a 1-byte value indicating the specific DTCSnapshot data record requested for a DTCMaskRecord via the reportDTCSnapshotByDTCNumber sub-function. 0x00 is reserved for legislated purposes. Values 0x01 to 0xFE are for manufacturer-specific use, and 0xFF requests all stored DTCSnapshot records at once.

Syntax of 0x19 SID Positive Response Message

Response Message Definition – Sub-Function = Report Snapshot Identification

Data byte	Parameter Name	Byte Value
#1	Read DTC Information +Ve Response SID	0x59
#2	Report Type = [                             report DTC Snapshot Identification ]	0x03
#3 #4 #5	DTC Record[]#1 = [                                     DTC High Byte#1                                     DTC Middle Byte#1                                     DTC Low Byte#1 ]	0x00 – 0xFF 0x00 – 0xFF 0x00 – 0xFF
#6	DTC Snapshot Record Number#1	0x00 – 0xFF
:	:	:
#n-3 #n-2 #n-1	DTC Record[]#m = [                                   DTC High Byte#m                                   DTC Middle Byte#m                                   DTC Low Byte#m ]	0x00 – 0xFF 0x00 – 0xFF 0x00 – 0xFF
#n	DTC Snapshot Record Number#m	0x00 – 0xFF
Certainly, here’s a shorter version: C1: DTC Record and DTC Snapshot Record Number are included only if DTC Snapshot records are available. C2: Additionally, they’re included only when multiple DTC Snapshot records are available.

SBFID (0x03) Response Message Data-Parameter of SID (0x19)

reportType: This parameter reflects bits 6 – 0 of the sub-function parameter from the client’s request message.

DTCRecord: This parameter record includes one or more groupings of DTCHighByte, DTCMiddleByte, and DTCLowByte. The interpretation of the DTCRecord depends on the value included in the DTCFormatIdentifier parameter, as defined in the following table:

DTCFormatIdentifier	Specification
SAE_J2012-DA_DTCFormat_00	ISO 15031-6 [12]
ISO_14229-1_DTCFormat	Vehicle manufacturer-defined
SAE_J1939-73_DTCFormat	SAE J1939-73 [19]
ISO_11992-4_DTCFormat	ISO 11992-4 [5]
SAE_2012-DA_WWHOBD_DTCFormat	ISO 27145-2 [16]

DTCRecord: This parameter record includes one or more groupings of DTCHighByte, DTCMiddleByte, and DTCLowByte. The interpretation of the DTCRecord is based on the DTCFormatIdentifier parameter value

DTCSnapshotRecordNumber: This parameter is either the echo of the DTCSnapshotRecordNumber specified by the client in the reportDTCSnapshotRecordByDTCNumber request, or the actual DTCSnapshotRecordNumber of a stored DTC snapshot record.

DTCSnapshotRecord: The DTCSnapshotRecord contains a snapshot of data values captured at the time of the system malfunction.

Syntax of 0x19 SID Negative Response Message

Response Message Definition – Sub-Function = Report Snapshot Identification

Data byte	Parameter Name	Byte Value
#1	Read DTC Information –Ve Response SID [ byte#1 ]	0x7F
#2	Requested SID [ byte#1 ]	0x19
#3	Negative Response Code [Byte#1]	NRC

Example of 0x03 Report DTC Snapshot Identification in UDS 0x19 Service

Below are the Examples of 0x03 Report DTC Snapshot Identification in UDS 0x19 Service:

Example of Request Message Frame Format of SBFID-0x03 for SID-0x19

ReadDTCInformation, sub-function = reportDTCSnapshotIdentification, request message flow Example

Message direction	Client → Server
Message Type	Request
Data Byte	Description (all values are in hexadecimal)	Byte Value
#1	Read DTC Information Request SID	0x19
#2	Sub-Function = reportDTCSnapshotIdentification,                  Suppress Pos Rsp Msg Indication Bit = FALSE	0x03

Example of Positive Response Message Frame Format of SBFID-0x03 for SID-0x19

ReadDTCInformation, sub-function = reportDTCSnapshotIdentification, positive response

Message direction	Server → Client
Message Type	Response
Data Byte	Description (all values are in hexadecimal)	Byte Value
#1	Read DTC Information +Ve Response SID	0x59
#2	Report Type = report DTC Snapshot Identification	0x03
#3 #4 #5 #6	DTC And Status Record#1 [ DTC High Byte ] DTC And Status Record#1 [ DTC Middle Byte ] DTC And Status Record#1 [ DTC Low Byte ] DTC Snapshot Record Number#1	0x12 0x34 0x56 0x01
#7 #8 #9 #10	DTC And Status Record#2 [ DTC High Byte ] DTC And Status Record#2 [ DTC Middle Byte ] DTC And Status Record#2 [ DTC Low Byte ] DTC Snapshot Record Number#2	0x12 0x34 0x56 0x02
#11 #12 #13 #14	DTC And Status Record #3 [ DTC High Byte ] DTC And Status Record#3 [ DTC Middle Byte ] DTC And Status Record#3 [ DTC Low Byte ] DTC Snapshot Record Number#3	0x78 0x9A 0xBC 0x01

Example of Negative Response Message Frame Format of SBFID-0x03 for SID-0x19

ReadDTCInformation, sub-function = reportDTCSnapshotIdentification, negative response

Message direction	Server → Client
Message Type	Response
Data Byte	Description (all values are in hexadecimal)	Byte Value
#1	Read DTC Information –Ve Response SID [ byte#1 ]	0x7F
#2	Requested SID [ byte#1 ]	0x19
#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-0x19
Request: Client --> Server
02 19 03
Positive Response: Server --> Client
14 59 03 12 34 56 01 12 34 56 02 78 9A BC 01
// Example for Negative Response for SID-0x19
Request: Client --> Server
03 19 03
Negative Response: Server --> Client
03 7F 19 13

CAN Data Format for UDS (DoCAN Protocol)

UDS over CAN follows a specific format where the first byte indicates the length of the data, followed by the SID and sub-functions.

Overview of UDS Protocol on CAN Bus:

The UDS protocol is commonly used in automotive diagnostics to communicate with Electronic Control Units (ECUs). It allows diagnostic tools to request various information, including DTCs (Diagnostic Trouble Codes), and provides mechanisms for querying and managing fault codes, ECU configurations, and system data.

In UDS, the Service ID (SID) identifies which service is being requested. The service in this case is 0x19, which is the Read DTC Information service. The sub-function 0x03 is used to request DTC Snapshot Identification.

1. Positive Response Example for SID 0x19 (Request to Read DTC Information)

Request (Client to Server):

02 19 03

• 02: Request Length (In this case, the length of the request is 3 bytes).
• 19: Service ID (SID) for the Read DTC Information service.
• 03: Sub-function for Report DTC Snapshot Identification (0x03) – requesting the snapshot associated with the stored DTCs.

The client (diagnostic tool) sends this message to the server (ECU) to request snapshot information related to Diagnostic Trouble Codes (DTCs).

Positive Response (Server to Client):

14 59 03 12 34 56 01 12 34 56 02 78 9A BC 01

• 14 – Total length of data.
• 59 – Positive Response Service ID (0x40 + 0x19)
• 03 – Echo of the requested sub-function
• 12 34 56 – First DTC code
• 01 – Status byte for the first DTC
• 12 34 56 – Second DTC code
• 02 – Status byte for the second DTC
• 78 9A BC – Third DTC code
• 01 – Status byte for the third DTC

This response tells the client that three DTCs are currently active and each is followed by its status byte, describing its state (e.g., confirmed, pending, etc.).

2. Negative Response Example for SID 0x19 (Request to Read DTC Information)

Request (Client to Server):

03 19 03

• 03: Request Length (In this case, the length of the request is 3 bytes).
• 19: Service ID (SID) for Read DTC Information service.
• 03: Sub-function for Report DTC Snapshot Identification (0x03), again requesting the snapshot associated with DTCs.

The client is sending the same request to the ECU, but this time, the response could be different (negative response) due to an error or condition.

Negative Response (Server to Client):

03 7F 19 13

• 03: Response Length (The response is 3 bytes).
• 7F: Negative Response Identifier (This indicates that the server is sending a negative response due to an error).
• 19: Service ID (SID) for Read DTC Information.
• 13: Negative Response Code.

The negative response code 0x13 means “Sub-function not supported”. This indicates that the sub-function requested (in this case, 0x03 Report DTC Snapshot Identification) is not supported by the ECU. It could be that the ECU does not have snapshot data, or it doesn’t implement that particular sub-function for reading DTC snapshot information.

Summary of Commands and Steps:

• Positive Response:
  • The client sends a request with SID 0x19 and Sub-function 0x03 (asking for DTC snapshot data).
  • The server (ECU) responds with a positive response (SID 0x59) and the requested snapshot data (indicating success).
• Negative Response:
  • The client sends a request with SID 0x19 and Sub-function 0x03.
  • If there’s an error (such as the sub-function not being supported by the ECU), the server responds with a negative response (SID 0x7F) and error code 0x13 (Sub-function not supported).

When is a Negative Response Expected?

A negative response can occur in several situations:

1. Sub-function not supported: The ECU does not support the requested sub-function (e.g., if the vehicle doesn’t store snapshot data).
2. Invalid parameters: If the parameters sent with the request are invalid or out of range.
3. Internal errors: The ECU may have encountered an error while processing the request.

In general, a negative response signifies that the ECU was unable to fulfill the request, and it provides a response code to explain why.

Importance of These Commands

These UDS commands are crucial for the diagnostic process in modern vehicles:

• They help automotive technicians retrieve vital data from ECUs for troubleshooting.
• Snapshot data provides additional context for faults, allowing technicians to better understand the conditions under which problems occurred.
• Negative responses help narrow down why a request failed, guiding technicians toward resolving ECU communication issues or identifying unsupported functions.