B1742 DTC Code: Understanding and Troubleshooting


In the realm of automotive diagnostics, DTC codes play a significant role in identifying and resolving issues within a vehicle. One such code is the B1742 DTC code. In this comprehensive article, we will delve into the details of the B1742 code, its meaning, common causes, and steps to troubleshoot it effectively. So let’s get started!

Understanding the B1742 DTC Code

The B1742 DTC code is primarily associated with a specific fault related to the secondary air injection system in many vehicles. In the OBD-II (On-Board Diagnostic) system, this code signifies an issue with the secondary air injection system relay control circuit. This code is often encountered in newer vehicles equipped with advanced emission control systems.

To better understand the B1742 DTC code, let’s break it down:

  • B: The “B” prefix indicates that the code is specific to the body of the vehicle, encompassing various electrical components and systems.
  • 1: The first digit of the code usually indicates a generic issue related to the body of the vehicle or multiple systems within it.
  • 7: The third digit signifies that the code is related to the secondary air injection system.
  • 4: The fourth digit indicates a specific fault within the secondary air injection system.
  • 2: The last digit provides additional information about the nature of the fault, specifically pertaining to the relay control circuit.

Common Causes of the B1742 DTC Code

Several factors can contribute to the generation of the B1742 DTC code. Identifying the underlying cause is crucial for effectively diagnosing and resolving the issue. Here are some primary causes to consider:

  1. Faulty relay: A faulty secondary air injection relay can trigger the B1742 code. This relay controls the activation and deactivation of the secondary air injection system, which aids in reducing vehicle emissions during cold starts.

  2. Wiring or connector issues: Damaged or poor-quality wiring harnesses and connectors associated with the secondary air injection system can contribute to the B1742 DTC code. Corrosion, loose connections, or wire breaks can disrupt the relay control circuit and trigger the code.

  3. ECU malfunctions: The Engine Control Unit (ECU) is responsible for managing various systems within the vehicle, including the secondary air injection system. A malfunction in the ECU may lead to the B1742 code.

  4. Faulty secondary air pump: The secondary air pump is an integral component of the secondary air injection system. If the pump becomes damaged or malfunctions, it can trigger the B1742 code.

Troubleshooting the B1742 DTC Code

Effectively diagnosing and resolving the B1742 DTC code requires a systematic approach. Here is a step-by-step guide to troubleshooting the code:

  1. Scan for additional codes: Begin by utilizing an OBD-II scanner to retrieve all stored codes. Ensure that you check for any additional codes related to the secondary air injection system. This will provide a comprehensive overview of potential issues and help pinpoint the root cause.

  2. Inspect wiring and connectors: Visually inspect the wiring harnesses, connectors, and associated components of the secondary air injection system. Look for any signs of physical damage, loose connections, or corrosion. Carefully repair or replace any damaged wiring or connectors as necessary.

  3. Test the secondary air injection relay: Use a multimeter to test the secondary air injection relay’s functionality. Ensure that the relay is receiving the necessary voltage and properly sending signals to activate the secondary air injection system. Replace the relay if found to be faulty.

  4. Check the secondary air pump: Inspect the secondary air pump for any signs of damage or malfunction. Listen for unusual noises or vibrations that may indicate a problem. If necessary, consult the vehicle’s repair manual for guidance on testing and replacing the pump.

  5. Examine the ECU: If all previous steps have been performed without resolving the B1742 code, it may be necessary to inspect the ECU. Consult a professional or refer to the vehicle’s repair manual for an in-depth analysis of the ECU’s functionality and potential troubleshooting methods.

Frequently Asked Questions (FAQs)

Q1: Can the B1742 DTC code cause any significant damage to the vehicle if left unresolved?

A1: While the B1742 code indicates a fault within the secondary air injection system relay control circuit, it is unlikely to cause any immediate damage or affect the vehicle’s drivability. However, it is advisable to address the issue promptly to maintain optimal performance and minimize potential concerns related to emissions.

Q2: Can I reset the B1742 code without addressing the underlying issue?

A2: Resetting the B1742 code without resolving the root cause will temporarily eliminate the error code from the system, but it will likely reappear once the vehicle undergoes emissions-related tests during regular driving conditions. It is essential to diagnose and fix the issue to prevent the code from resurfacing.

Q3: Can I troubleshoot the B1742 code without professional assistance?

A3: While some basic troubleshooting steps, such as inspecting wiring and connectors, can be performed by vehicle owners with appropriate knowledge and tools, diagnosing and repairing the B1742 code may require extensive expertise. To ensure an accurate diagnosis and effective resolution, it is recommended to consult a qualified automotive technician or refer to the vehicle’s repair manual for guidance.


The B1742 DTC code pertaining to the secondary air injection system relay control circuit can be resolved by following a systematic troubleshooting process. By scanning for additional codes, inspecting wiring and connectors, and testing the relay and secondary air pump, you can effectively diagnose and resolve the issue. If necessary, consult a professional for further guidance and expertise. Remember, addressing the B1742 DTC code promptly will help maintain your vehicle’s optimal performance and adhere to emission control standards.

About author


Meet Sam Mitchell, your experienced and reliable guide in the complex world of car fault codes. With a robust career spanning over 15 years as a professional car mechanic, John has the skills, knowledge, and practical experience to help you navigate car fault issues with confidence.


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