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P0418 Lexus Code - Secondary Air Injection System Relay 'A' Circuit Malfunction

Quick Answer

The P0418 diagnostic trouble code (DTC) for Lexus vehicles refers to a malfunction in the Secondary Air Injection System Relay 'A' circuit. Common causes include Faulty Relay: The most common cause of this code is a faulty relay that controls the secondary air injection system, Wiring Issues: Damage or corrosion to the wiring connected to the relay can also trigger this code, Relay Control Module Failure: A malfunction in the relay control module can prevent the relay from operating correctly. Severity is Moderate - service should be scheduled soon. The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.

What it means
P0418 Lexus indicates Secondary Air Injection System Relay 'A' Circuit Malfunction.
Common causes
Common causes include Faulty Relay: The most common cause of this code is a faulty relay that controls the secondary air injection system, Wiring Issues: Damage or corrosion to the wiring connected to the relay can also trigger this code, Relay Control Module Failure: A malfunction in the relay control module can prevent the relay from operating correctly.
Severity
Moderate - service should be scheduled soon.
Can I drive?
The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.
What is this?
Table of contents Created and updated by William Orellana on Sep 12, 2024
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Code P0418 Lexus Description

The P0418 diagnostic trouble code (DTC) for Lexus vehicles refers to a malfunction in the Secondary Air Injection System Relay 'A' circuit. The secondary air injection system is designed to reduce harmful emissions by injecting fresh air into the exhaust system during cold engine starts. This code indicates that there is an issue with the relay that controls the secondary air injection system, which can lead to improper operation of the system.

OBDII Code P0418 Lexus - Secondary Air Injection System Relay 'A' Circuit Malfunction
P0418 Lexus Code - Secondary Air Injection System Relay 'A' Circuit Malfunction

Common Causes of P0418 Lexus

  1. Faulty Relay: The most common cause of this code is a faulty relay that controls the secondary air injection system.
  2. Wiring Issues: Damage or corrosion to the wiring connected to the relay can also trigger this code.
  3. Relay Control Module Failure: A malfunction in the relay control module can prevent the relay from operating correctly.
  4. Vacuum Leaks: Any leaks in the vacuum system that supplies air to the secondary air injection system can cause this code to be triggered.

Symptoms of P0418 Lexus

  1. Check Engine Light: The most common symptom associated with this code is the illumination of the check engine light on the vehicle's dashboard.
  2. Decreased Fuel Efficiency: A malfunctioning secondary air injection system can lead to decreased fuel efficiency due to improper combustion.
  3. Rough Idle: The engine may experience rough idling or stalling as a result of the malfunction.
  4. Increased Emissions: The vehicle may produce higher emissions than normal, potentially leading to a failed emissions test.

How to Fix P0418 Lexus

  1. Diagnose the Issue: Begin by using a diagnostic scanner to retrieve the specific trouble code and identify the source of the problem.
  2. Inspect Relay and Wiring: Check the relay and wiring for any signs of damage or corrosion, and repair or replace as needed.
  3. Test Relay Control Module: Test the relay control module to ensure it is functioning properly, and replace if necessary.
  4. Check for Vacuum Leaks: Inspect the vacuum system for leaks and repair any issues found.
  5. Clear Codes and Test: Once the repairs have been completed, clear the trouble codes from the vehicle's computer and test the system to ensure the issue has been resolved.

Cost to Fix P0418 Lexus

The typical repair costs for addressing a P0418 code on a Lexus vehicle can range from $150 to $400, depending on the specific repairs needed and the cost of parts. This estimate includes the cost of parts such as a new relay or wiring components, as well as labor costs for diagnosis and repair. It's important to note that labor rates at auto repair shops can vary, so it's advisable to check with local shops for a more accurate estimate based on your location and vehicle model.

When is the Code Detected?

The DTC P0418 is detected the the AIR vacuum control solenoid circuit not operating as desired by the PCM.

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

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