AutoCodes – Mercedes-Benz – P0418 Mercedes-Benz

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

Quick Answer

An air pump is used on the vehicle to lower tail pipe emissions on start-up. Common causes include Faulty Air Pump inoperative, Air bypass solenoid harness is open or shorted, Air bypass solenoid circuit poor electrical connection. 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 Mercedes-Benz indicates Secondary Air Injection System Relay 'A' Circuit Malfunction.
Common causes: Common causes include Faulty Air Pump inoperative, Air bypass solenoid harness is open or shorted, Air bypass solenoid circuit poor electrical connection.
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.

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Code Popularity 11,938

How popular is this code, among other codes? Low

Repair Importance Level

Moderate (Service soon) (2 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on Apr 18, 2019

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P0418 Mercedes-Benz Description

An air pump is used on the vehicle to lower tail pipe emissions on start-up. The Powertrain Control Module (PCM) grounds the Air pump relay control circuit which energizes the Air pump. The PCM also grounds the Air combination valve vacuum control solenoid circuit, which energizes the Air vacuum control solenoid. Vacuum is then applied to both Air combination valve diaphragms which opens the shut off valves. The PCM enables both circuits simultaneously when Air system operations id desired. When the AIR system is active, then Air pump forces fresh air into the exhaust stream in order to accelerate catalyst operation. The AIR combination valves replace the conventional check valves. When the AIR system is inactive the shut off valves prevent air flow in either direction.

OBDII Code P0418 Mercedes-Benz - Secondary Air Injection System Relay 'A' Circuit Malfunction - AutoCodes.com — P0418 Mercedes-Benz Code - Secondary Air Injection System Relay 'A' Circuit Malfunction

What does this mean?

What are the Possible Causes of the DTC P0418 Mercedes-Benz?

Faulty Air Pump inoperative
Air bypass solenoid harness is open or shorted
Air bypass solenoid circuit poor electrical connection

How to Fix the DTC P0418 Mercedes-Benz?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0418 Mercedes-Benz code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P0418 Mercedes-Benz code?

Need more information on how to fix the P0418 Mercedes-Benz code? Get Access to Factory Service Manuals

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Get the P0418 Mercedes-Benz code diagnosed by a professional: Find a repair shop in your area

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.

Frequently Asked Questions about P0418 Mercedes-Benz Code

1. What are the common symptoms of OBDII code P0418 in a Mercedes-Benz?

The common symptoms of code P0418 include the illumination of the Check Engine Light on the dashboard, rough idling, decreased engine performance, and potential exhaust system issues.

2. What can cause the OBDII code P0418 to trigger in a Mercedes-Benz?

The most common cause of code P0418 in a Mercedes-Benz is a malfunctioning secondary air injection system relay 'A', which controls the flow of air into the exhaust system for emission control purposes.

3. How does the secondary air injection system relay 'A' malfunction lead to code P0418 in a Mercedes-Benz?

When the secondary air injection system relay 'A' malfunctions, it may fail to properly regulate the flow of air into the exhaust system, triggering the OBDII code P0418 due to a detected circuit malfunction.

4. Can a faulty secondary air injection system relay 'A' be repaired in a Mercedes-Benz?

In some cases, the secondary air injection system relay 'A' can be repaired by cleaning or replacing the relay itself. However, it is recommended to diagnose the root cause of the malfunction to prevent further issues.

5. How can I diagnose and repair OBDII code P0418 in my Mercedes-Benz?

Diagnosing and repairing code P0418 involves checking the secondary air injection system relay 'A' for proper functionality, inspecting related wiring and connections, and ensuring the air injection system components are working correctly.

6. Are there any DIY tips for troubleshooting OBDII code P0418 in a Mercedes-Benz?

DIY enthusiasts can start by visually inspecting the secondary air injection system relay 'A' for any signs of damage or corrosion. Additionally, checking the relay's connections and related wiring can help identify potential issues.

7. Can driving with OBDII code P0418 illuminated cause further damage to a Mercedes-Benz?

Continuing to drive with code P0418 illuminated may lead to decreased fuel efficiency, increased emissions, and potential damage to the catalytic converter or other emission control components over time.

8. Is it safe to clear OBDII code P0418 in a Mercedes-Benz without repairing the issue?

Clearing the OBDII code P0418 without addressing the underlying problem with the secondary air injection system relay 'A' can temporarily turn off the Check Engine Light, but the issue may persist and trigger the code again.

9. How much does it typically cost to repair OBDII code P0418 in a Mercedes-Benz at a professional mechanic?

The cost of repairing code P0418 can vary depending on the extent of the issue and the labor rates of the mechanic. On average, the repair cost can range from $200 to $500, including parts and labor.

10. Can OBDII code P0418 in a Mercedes-Benz be prevented in the future?

Regular maintenance and inspection of the secondary air injection system components, including the relay 'A', can help prevent the occurrence of code P0418. Additionally, addressing any related issues promptly can aid in avoiding future problems.