Report First Confirmed DTC (0x0C) in UDS Protocol 0x19 SID: Complete Guide for Diagnostics

Hello, automotive diagnostics enthusiasts! In this blog post, we’ll explore Report First Confirmed DTC (0x0C) in UDS – one of the most vital sub-functions in the UDS (Uni

fied Diagnostic Services) protocol: Report First Confirmed DTC (0x0C) under Service 0x19. This feature is crucial for retrieving the earliest confirmed Diagnostic Trouble Code (DTC) recorded by a vehicle’s ECU. Understanding how this works helps technicians and engineers identify and resolve the root cause of a fault more efficiently. We’ll break down how the request and response work, what conditions affect the response, and why preserving the first confirmed DTC is important even after aging criteria are met. Whether you’re new to UDS or deepening your knowledge, this guide will clarify the role of 0x0C in automotive diagnostics. Let’s dive in and decode how it all works!

Introduction to Report First Confirmed DTC (0x0C) in UDS Protocol: Service 0x19

In the world of automotive diagnostics, understanding how Diagnostic Trouble Codes (DTCs) are reported is crucial for effective fault detection and resolution. One such important feature provided by the UDS (Unified Diagnostic Services) protocol is the Report First Confirmed DTC, identified by sub-function 0x0C under Service 0x19. This service allows a diagnostic tester to retrieve the very first DTC that was confirmed and logged by the vehicle’s control unit. Knowing the first confirmed DTC helps technicians trace back to the origin of a fault, even if other DTCs were logged later. In this article, we’ll explore how the 0x0C sub-function works, the structure of its request and response messages, and the conditions that affect the returned data. Whether you’re a beginner or an experienced engineer, understanding this function will enhance your grasp of UDS diagnostics. Let’s begin!

What is Report First Confirmed DTC (0x0C) in UDS Protocol: Service 0x19?

In the UDS (Unified Diagnostic Services) protocol, which is widely used in modern automotive ECUs for diagnostics and communication, Service 0x19 is designated for ReadDTCInformation. This service provides access to stored Diagnostic Trouble Codes (DTCs), helping technicians or diagnostic tools understand the health status of vehicle systems.

One of the key sub-functions under Service 0x19 is 0x0C, known as ReportFirstConfirmedDTC. This sub-function allows the diagnostic client (typically a scan tool or tester) to retrieve the first DTC that was confirmed by the ECU after the last time DTCs were cleared. It’s especially useful for identifying the original root cause of a fault when multiple DTCs have been recorded.

How It Works?

1. Client Request:
   • The client sends a diagnostic request to the ECU using:
     • Service ID (SID): 0x19 (ReadDTCInformation)
     • Sub-function: 0x0C (Report First Confirmed DTC)
   • Optional parameters like the DTCStatusAvailabilityMask may be included to filter or interpret the DTC status.
2. Server (ECU) Response:
   • If there is at least one confirmed DTC since the last time DTCs were cleared, the ECU will return:
     • A DTCStatusAvailabilityMask byte.
     • The DTC number (3 bytes).
     • The DTC status (1 byte).
   • If no confirmed DTCs exist, the ECU will respond only with the DTCStatusAvailabilityMask and no DTC data following it.

Important Behavior Rules:

• If only one DTC has become confirmed, both 0x0C (first confirmed) and 0x0E (most recent confirmed) sub-functions will return the same DTC.
• The first confirmed DTC remains stored even if it later satisfies the aging criteria and is considered “aged out,” unless the client sends a ClearDiagnosticInformation (Service 0x14) request.
• This feature ensures that even if the issue is temporarily resolved or masked by other faults, you can still trace the very first confirmed issue, aiding in effective root-cause analysis.

Why do we need Report First Confirmed DTC (0x0C) in UDS Protocol: Service 0x19?

The Report First Confirmed DTC (0x0C) sub-function in Service 0x19 of the UDS protocol plays a critical role in identifying the root cause of faults in modern vehicle diagnostics. In real-world automotive systems, multiple DTCs can be triggered almost simultaneously due to cascading issues. Without knowing which fault occurred first, technicians may misinterpret the sequence of events and address symptoms instead of the actual cause.

Here’s why this sub-function is essential:

1. Root Cause Identification

In automotive diagnostics, it’s common for multiple faults to occur simultaneously, making it difficult to determine the exact origin of a problem. The Report First Confirmed DTC (0x0C) sub-function helps resolve this by providing the first confirmed DTC since the last diagnostic reset. By knowing which fault was first, technicians can directly address the root cause of the problem, rather than wasting time on secondary or unrelated faults. This ensures that the actual issue is prioritized for repair, improving the overall efficiency of the diagnostic process.

2. Accurate Troubleshooting

When several DTCs are logged, it can be challenging to know which one is the initial fault. The Report First Confirmed DTC helps solve this by identifying the first confirmed issue, which is often the root cause that triggers additional faults. By pinpointing the sequence of failures, technicians can approach troubleshooting more effectively, tackling the primary issue before dealing with secondary ones. This leads to a more focused and accurate repair process, reducing the likelihood of misdiagnosing the problem.

3. Persistent Record of First Fault

Even if the first confirmed DTC is no longer active due to aging criteria or temporary recovery, the ECU retains a record of it until a ClearDiagnosticInformation request is made. This persistent storage allows the diagnostic tool to access historical fault data, even when the fault condition has been resolved or is no longer present. This feature is especially useful for diagnosing intermittent issues or faults that are difficult to reproduce, as it preserves valuable diagnostic history for future reference and analysis.

4. Improved Efficiency in Service Operations

The Report First Confirmed DTC (0x0C) function speeds up the diagnostic process by allowing technicians to focus directly on the first fault that caused the issue. Instead of manually sifting through multiple DTCs to determine which one is the root cause, technicians can get a clear and immediate indication of the primary problem. This not only saves time but also enhances overall repair efficiency, which is especially valuable in high-demand service environments where quick turnaround is crucial.

5. Compliance, Warranty, and Emissions Diagnostics

Manufacturers and regulatory authorities often require that the first confirmed DTC be identified and logged for compliance, especially for warranty claims or emissions-related diagnostics. By using the Report First Confirmed DTC function, manufacturers can verify that the correct fault was addressed, ensuring that all necessary repairs were performed in accordance with industry standards. It also supports emissions testing by identifying the original source of a fault, helping technicians ensure compliance with environmental regulations.

6. Integration with Diagnostic Tools

Many modern diagnostic scan tools and service platforms integrate the Report First Confirmed DTC function to provide users with a seamless, automated diagnostic experience. These tools rely on this sub-function to automatically display the first confirmed fault in their diagnostic reports or logs. This makes it easier for technicians to track and resolve issues efficiently. Furthermore, it helps improve the overall usability and functionality of diagnostic platforms, making them more intuitive and user-friendly.

7. Enhanced Data-Driven Decision Making

The Report First Confirmed DTC (0x0C) provides valuable historical fault data, enabling service teams to make better-informed decisions based on reliable diagnostic information. By knowing which DTC was confirmed first, service technicians can assess whether the fault is part of an ongoing issue or if it has been properly resolved in the past. This data-driven approach helps in making strategic decisions regarding vehicle repairs, maintenance, and parts replacement, ultimately enhancing service quality and customer satisfaction.

Report First Confirmed DTC (0x0C) in UDS Protocol: Service 0x19

The sub-function 0x0C in the UDS protocol allows the diagnostic client to request the first confirmed Diagnostic Trouble Code (DTC) stored by the server. When this request is made, the server responds with the DTCStatusAvailabilityMask followed by the earliest confirmed DTC and its current status only if such a DTC exists.

If no confirmed DTCs have been recorded since the last successful execution of the ClearDiagnosticInformation service, then the response will contain only the DTCStatusAvailabilityMask, and no DTC data will follow. This ensures accurate feedback based on the latest clearing action.

Interestingly, if just one DTC has been confirmed since the last clearing event, it will be returned as the first confirmed DTC, even if it is also the most recent one. This simplifies tracking for single-fault conditions. Moreover, even if the first confirmed DTC has aged out (i.e., it met aging criteria and is no longer active), its record is still retained and will be provided in the response, assuming no new DTCs were confirmed in the meantime.

Syntax of Report First Confirmed DTC (SBFID-0x0C) of SID-0x19

Request Message Definition – Sub-function = Report First Confirmed DTC

Data byte	Parameter Name	Byte Value
#1	Read DTC Information Request SID	0x19
#2	sub-function = [ report Type =                             Report First Confirmed DTC ]	0x0C

Syntax of 0x19 SID Positive Response Message

Response Message Definition – Sub-function = Report First Confirmed DTC

Data byte	Parameter Name	Byte Value
#1	Read DTC Information +Ve Response SID	0x59
# 2	Report Type = [                               Report First Confirmed DTC ]	0x0C
#3	DTC Status Availability Mask	0x00 – 0xFF
#4 #5 #6 #7 #8 #9 #10 #11 : #n-3 #n-2 #n-1 #n	DTC And Status Record[] = [                                           DTC High Byte#1                                                 DTC Middle Byte#1                                                 DTC Low Byte#1                                                      status Of DTC#1                                                 DTC High Byte#2                                                 DTC Middle Byte#2                                                   DTC Low Byte#2                                                      status OfDTC#2                                                                   :                                                      DTC High Byte#m                                                      DTC Middle Byte#m                                                  DTC Low Byte#m                                                      status Of DTC#m	0x00 – 0xFF 0x00 – 0xFF 0x00 – 0xFF 0x00 – 0xFF 0x00 – 0xFF 0x00 – 0xFF 0x00 – 0xFF 0x00 – 0xFF : 0x00 – 0xFF 0x00 – 0xFF 0x00 – 0xFF 0x00 – 0xFF
C1: This parameter is only present if DTC information is available to be reported. C2: This parameter is only present if reportType = reportSupportedDTCs, reportDTCByStatusMask, reportMirrorMemoryDTCByStatusMask, reportEmissionsOBDDTCByStatusMask, reportDTCWithPermanentStatus and more than one DTC information is available to be reported.

SBFID (0x0C) 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.

DTCStatusAvailabilityMask: A byte where the bits are defined the same as the statusOfDTC, representing the status bits supported by the server. Bits not supported by the server will be set to ‘0’. Each supported bit (indicated by a value of ‘1’) will be implemented for every DTC supported by the server.

DTCAndStatusRecord: This parameter record includes one or more groupings of DTCHighByte, DTCMiddleByte, DTCLowByte, and statusOfDTC, based on the following formats:

Supported DTC Formats:

• ISO_14229-1_DTCFormat
• SAE_J2012-DA_DTCFormat_00
• SAE_J1939-73_DTCFormat
• SAE_J2012-DA_DTCFormat_04
• ISO_11992-4_DTCFormat

• DTCHighByte, DTCMiddleByte, DTCLowByte: Together represent a unique identification number for a specific diagnostic trouble code.
  • DTCHighByte and DTCMiddleByte: Represent the circuit/system being diagnosed.
  • DTCLowByte: Indicates the type of fault (e.g., sensor open circuit, sensor shorted to ground).

Formats Supported:

• SAE_J2012-DA_DTCFormat_04
• SAE_J2012-DA_DTCFormat_00
• ISO_14229-1_DTCFormat
• SAE_J1939-73_DTCFormat
• ISO11992-4DTCFormat

Syntax of 0x19 SID Negative Response Message

Response Message Definition – Sub-Function = Report First Confirmed DTC

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 Report First Confirmed DTC (0x0C) in UDS Protocol: Service 0x19

Here are the Examples of Report First Confirmed DTC (0x0C) in UDS Protocol Service 0x19:

Example of Request Message Frame Format of SBFID-0x0C for SID-0x19

Read DTC Information, Sub-Function = Report First Confirmed DTC, Request Message Flow Example

// 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 0C
Positive Response: Server --> Client
15 59 0C FF 12 34 56 26 C0 AC 08 A4 17 91 03 BC
// Example for Negative Response for SID-0x19
Request: Client --> Server
03 19 0C Negative Response: Server --> Client
03 7F 19 13

Understanding UDS Commands Over CAN: Example for SID 0x19 and Sub-Function 0x0C

In the Unified Diagnostic Services (UDS) protocol, communication between the diagnostic tester (client) and the ECU (server) occurs using specific service identifiers (SIDs). The 0x19 service is used for ReadDTCInformation, and sub-function 0x0C specifically requests the first confirmed DTC stored in the ECU. Below is a breakdown of how these commands and responses work over CAN.

UDS Request: Client → Server

02 19 0C

Explanation of the Code:

• 02 → Indicates the length of the data that follows (2 bytes: 0x19 and 0x0C).
• 19 → Service Identifier (SID) for ReadDTCInformation.
• 0C → Sub-function for ReportFirstConfirmedDTC.

The client is asking the ECU: “Please report the first confirmed DTC since the last time DTCs were cleared.”

Positive Response: Server → Client

15 59 0C FF 12 34 56 26 C0 AC 08 A4 17 91 03 BC

Explanation of the Code:

• 15: Indicates 21 bytes of total data (might be part of a multi-frame message).
• 59: Positive response to service 0x19 (0x19 + 0x40).
• 0C: Echoes the requested sub-function.
• FF: Snapshot record number.
• 12 34 56: Example DTC – 0x123456.
• 26: Snapshot record ID or count.
• C0 AC 08 A4 17 91 03 BC: Snapshot data values, possibly RPM, temperature, voltage, etc.

The server provides the DTC 0x123456 snapshot record number 26, with detailed parameter values that describe the exact moment the fault was detected.

Negative Response: Server → Client

03 7F 19 13

Explanation of the Code:

• 03 → Length of the response (3 bytes follow).
• 7F → Indicates a negative response.
• 19 → The original service ID that caused the negative response.
• 13 → NRC (Negative Response Code) → 0x13 means “Invalid Format”.

Key Takeaways:

• This indicates an error in the request. Possible reasons include:
  • Wrong data length.
  • Missing required bytes.
  • Malformed structure in the request frame.