Understanding “Report DTC Fault Detection Counter (0x14)” in UDS Protocol 0x19 Service

Hello, automotive diagnostics enthusiasts! In this blog post, I will introduce you to an important and insightful sub-function of the UDS protocol: Report DTC Fault Detection

Counter (0x14), part of the 0x19 Diagnostic Service. This sub-function helps retrieve valuable data about how often a specific Diagnostic Trouble Code (DTC) was detected by the ECU. It plays a crucial role in understanding fault behavior over time and is essential for detailed diagnostics and root cause analysis. In this post, I will explain what the fault detection counter is, how it is requested and interpreted, and when to use it effectively. We’ll also explore the structure of request and response messages on the CAN bus. By the end, you’ll clearly understand how to use this sub-function in real diagnostic workflows. Let’s dive into the world of UDS diagnostics!

Introduction to “Report DTC Fault Detection Counter (0x14)” in UDS Protocol 0x19 Service

In the world of automotive diagnostics, the Unified Diagnostic Services (UDS) protocol plays a key role in reading and managing fault codes from vehicle ECUs. One of its powerful sub-functions is “Report DTC Fault Detection Counter (0x14)”, which belongs to the 0x19 service (ReadDTCInformation). This sub-function allows a diagnostic tester or scan tool to request the number of times a specific Diagnostic Trouble Code (DTC) has been detected by the ECU. The fault detection counter provides valuable insight into how frequently a fault has occurred, aiding technicians in determining whether an issue is intermittent, persistent, or resolved. Understanding this counter is essential for effective troubleshooting, emission analysis, and repair verification. In this article, we’ll explore how this sub-function works, how it is implemented over the CAN bus, and how to interpret its response data accurately.

What is “Report DTC Fault Detection Counter (0x14)” in UDS Protocol 0x19 Service?

In the UDS (Unified Diagnostic Services) protocol, the service with Service ID 0x19 (ReadDTCInformation) is used to request various types of Diagnostic Trouble Code (DTC) information from an Electronic Control Unit (ECU). The sub-function 0x14, known as “Report DTC Fault Detection Counter”, is used to retrieve the fault detection counter value for a specific DTC.

This counter represents how many times the ECU has detected the fault condition associated with that DTC since the last memory clear or since a defined reset. It is an 8-bit counter maintained internally by the ECU, and its value helps diagnostic tools or service engineers understand how frequent or severe a specific fault is.

• The response includes:
  • A status availability mask
  • The DTC value queried
  • The current detection counter value

• This sub-function is especially useful for:
  • Determining the frequency of an intermittent fault
  • Deciding whether a repair was effective
  • Supporting warranty and emissions-related diagnostics

Why do we need “Report DTC Fault Detection Counter (0x14)” in UDS Protocol 0x19 Service?

Here’s the detailed explanation of why we need “Report DTC Fault Detection Counter (0x14)” in the UDS Protocol 0x19 Service:

1. To Track Fault Frequency

The Report DTC Fault Detection Counter helps track how often a particular fault has occurred in the vehicle’s system. By providing the number of times a Diagnostic Trouble Code (DTC) has been detected, it allows technicians to distinguish between intermittent faults and persistent issues. This information is crucial for prioritizing repairs and understanding the severity of the problem. A high counter value usually indicates a recurring issue that requires immediate attention, whereas a low value may suggest a one-time or minor anomaly.

2. To Support Effective Troubleshooting

Having access to the fault detection counter greatly improves troubleshooting accuracy. It provides insight into the fault’s behavior over time, helping technicians decide whether the fault is still active or sporadic. This enables them to make more informed decisions about what component or system to investigate further. By understanding the frequency and pattern of faults, diagnostics become more precise, saving time and reducing unnecessary part replacements.

3. To Evaluate Repair Success

After repairing a fault, the fault detection counter is useful to verify whether the repair was successful. If the counter resets or remains unchanged after the repair, it indicates that the fault condition no longer occurs. Conversely, if the counter continues to increase, it suggests that the fault is still present and may need further investigation. This helps avoid repeated repairs and provides confidence to technicians and vehicle owners about the effectiveness of maintenance.

4. To Ensure Compliance with Emission Standards

Emission regulations require detailed monitoring and reporting of faults related to the vehicle’s emission control systems. The fault detection counter plays a vital role in this by tracking how many times emission-related faults occur. It ensures that persistent emission issues are detected and addressed promptly, helping vehicles comply with environmental standards. This data supports regulatory inspections and assists in maintaining overall vehicle emission health.

5. To Enable Smart ECU Behavior

Modern ECUs use the fault detection counter internally to make smarter decisions about warning signals such as the Check Engine Light (MIL). Instead of illuminating the warning for every minor or momentary fault, the ECU considers the counter to determine if the fault is persistent enough to alert the driver. This reduces false alarms and improves the reliability of warnings, ensuring drivers are alerted only when genuine issues exist.

6. To Enhance Diagnostic Tool Reporting

Diagnostic scan tools use the fault detection counter to provide users with deeper insights into vehicle health. Displaying this counter allows both technicians and vehicle owners to better understand the nature and frequency of detected faults without needing to interpret raw ECU data. This improved visibility leads to more informed decision-making, better maintenance planning, and clearer communication between technicians and customers.

7. To Assist in Warranty and Vehicle History Analysis

The fault detection counter provides valuable data for warranty claims and vehicle history assessments. By documenting how frequently a fault occurred before a repair, manufacturers and service centers can verify whether a problem was persistent or just a rare incident. This helps in making fair warranty decisions and offers transparency in vehicle maintenance history. It also supports fleet managers and used car buyers by providing detailed fault occurrence records, which can influence servicing and resale value.

“Report DTC Fault Detection Counter (0x14)” in UDS Protocol 0x19 Service

The sub-function 0x14, known as Report DTC Fault Detection Counter, enables the client to retrieve a list of all current “prefailed” Diagnostic Trouble Codes (DTCs). These DTCs may or may not have been marked as “pending” or “confirmed” at the time the request is made. The purpose of the Fault Detection Counter is to provide a straightforward way to identify faults that are either developing or intermittent issues that might not be clearly indicated by the standard status byte of a DTC. How this counter is implemented internally varies between vehicle manufacturers. One key application of monitoring “prefailed” DTCs is during manufacturing, where it helps accelerate fault detection for problems that need time to fully manifest, a delay that manufacturing tests cannot afford. Additionally, this functionality proves useful in service scenarios after repairs or component replacements to quickly identify emerging faults.

Syntax of Report Supported DTC (SBFID-0x14) of SID-0x19

Request Message Definition – Sub-Function = Report DTC Fault Detection Counter

Data byte	Parameter Name	Byte Value
#1	Read DTC Information Request SID	0x19
#2	sub-function = [ report Type =                                          Report DTC Fault Detection Counter ]	0x0A

SBFID (0x14) 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.

Syntax of 0x19 SID Positive Response Message

Response Message Definition – Sub-Function = Report DTC Fault Detection Counter

Data byte	Parameter Name	Byte Value
#1	Read DTC Information +Ve Response SID	0x59
#2	report Type =     [            Report DTC Fault Detection Counter ]	0x14
#3 #4 #5 #6 #7 #8 #9 #10 #n-3 #n-2 #n-1 #n	DTCFaultDetectionCounterRecord[] = [ DTCHighByte#1 DTCMiddleByte#1 DTCLowByte#1 DTCFaultDetectionCounter#1 DTCHighByte#2 DTCMiddleByte#2 DTCLowByte#2 DTCFaultDetectionCounter#2 : DTCHighByte#m DTCMiddleByte#m DTCLowByte#m DTCFaultDetectionCounter#m ]	0x00 – 0xFF 0x00 – 0xFF 0x00 – 0xFF 0x01 – 0xFF 0x00 – 0xFF 0x00 – 0xFF 0x00 – 0xFF 0x01 – 0xFF : 0x00 – 0xFF 0x00 – 0xFF 0x00 – 0xFF 0x01 – 0xFF
C1: This parameter is only present if at least one DTC has a DTCFaultDetectionCounter with a positive value less than 0x7F. C2: This parameter record is only present if more than one DTC has a DTCFaultDetectionCounter with a positive value less than 0x7F.

SBFID (0x14) 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.

DTC Fault Detection Counter Record:

The DTCFaultDetectionCounterRecord is a structured data element that includes one or more Diagnostic Trouble Codes (DTCs), along with a corresponding value that represents the detection counter for each DTC. This record helps provide detailed insights into each fault.

DTC Fault Detection Counter:

The DTCFaultDetectionCounter itself indicates how many times a specific DTC has been identified by the system. It essentially tracks the frequency of fault detection, offering a deeper understanding of how often a particular issue is occurring. This information is particularly useful for diagnosing intermittent problems and monitoring the development of faults over time.

Syntax of 0x19 SID Negative Response Message

Response Message Definition – Sub-Function = Report DTC Fault Detection Counter

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 DTC Fault Detection Counter (0x14)” in UDS Protocol 0x19 Service

Here are the Examples of “Report DTC Fault Detection Counter (0x14)” in UDS Protocol 0x19 Service:

// 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 14
Positive Response: Server --> Client
11 59 14 00 01 D0 09 AA 11 02 AC 0E
// Example for Negative Response for SID-0x19
Request: Client --> Server
03 19 14
Negative Response: Server --> Client
03 7F 19 13

UDS Command Steps for Report DTC Fault Detection Counter (0x14)

The following example demonstrates how the Unified Diagnostic Services (UDS) commands are transmitted and received using the CAN protocol, following the DoCAN (Diagnostics over CAN) standard. This focuses on sub-function 0x14 of Service 0x19, which is used to report the DTC Fault Detection Counter.

1. Positive Response Example for SID 0x19 with Sub-function 0x14

🔹 Request: Client → Server

02 19 14

• 02 → Number of following data bytes (2 bytes: 19 14)
• 19 → Service Identifier (SID) for ReadDTCInformation
• 14 → Sub-function code for ReportDTCFaultDetectionCounter

This request asks the server to return the Fault Detection Counter values for supported DTCs.

🔹 Positive Response: Server → Client

11 59 14 00 01 D0 09 AA 11 02 AC 0E

• 11: PCI byte – total length of response.
• 59: Positive response code (0x40 + 0x19).
• 14: Echoed sub-function (0x14).
• 00 01 D0: DTC value being reported.
• 09 AA 11 02 AC 0E: Extended data record related to the reported DTC.

These extended data bytes (09 AA 11 02 AC 0E) are usually manufacturer-defined and can represent runtime information like:

• Number of DTC occurrences.
• Ignition cycles since last failure.
• Temperature, voltage, or other signal values when the fault occurred.

2. Negative Response Example for SID 0x19 with Sub-function 0x14

🔹 Request: Client → Server

03 19 14

• 03 → Indicates 3 bytes follow
• 19 → Service Identifier (ReadDTCInformation)
• 14 → Sub-function code (ReportDTCFaultDetectionCounter)

Here, the client might have added more parameters (depending on implementation), or used unsupported values.

🔹 Negative Response: Server → Client

03 7F 19 13

• 03 → Number of following bytes
• 7F → Negative Response indicator
• 19 → Service Identifier that caused the error
• 13 → Negative Response Code (NRC)

0x13 typically means “Invalid Format” – the server did not understand the structure of the request, possibly due to wrong data length or unsupported parameter combination.

These UDS messages show how clients and ECUs communicate diagnostic requests and responses using the CAN protocol. Understanding the structure of both positive and negative responses is essential for troubleshooting and proper diagnostic tool development. The ReportDTCFaultDetectionCounter service is especially helpful in identifying intermittent or developing faults early during testing or in service diagnostics.