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Engine-Codes – Generic – P0408

P0408 Code - Exhaust Gas Recirculation Sensor 'B' Circuit High

Quick Answer

The P0408 diagnostic trouble code (DTC) indicates a problem with the Exhaust Gas Recirculation (EGR) sensor 'B' circuit being too high. Common causes include Faulty EGR sensor 'B', Wiring or connector issues in the EGR sensor circuit, Carbon buildup in the EGR system. 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
P0408 indicates Exhaust Gas Recirculation Sensor 'B' Circuit High.
Common causes
Common causes include Faulty EGR sensor 'B', Wiring or connector issues in the EGR sensor circuit, Carbon buildup in the EGR system.
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 08, 2024
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Code P0408 Description

The P0408 diagnostic trouble code (DTC) indicates a problem with the Exhaust Gas Recirculation (EGR) sensor 'B' circuit being too high. The EGR system is responsible for reducing nitrogen oxide emissions by recirculating a portion of the exhaust gases back into the engine's intake system. The EGR sensor 'B' monitors the EGR system's performance and sends signals to the engine control module (ECM) to adjust the EGR valve's operation.

OBDII Code P0408 - Exhaust Gas Recirculation Sensor 'B' Circuit High
P0408 Code - Exhaust Gas Recirculation Sensor 'B' Circuit High

Common Causes of P0408

  1. Faulty EGR sensor 'B'
  2. Wiring or connector issues in the EGR sensor circuit
  3. Carbon buildup in the EGR system
  4. Vacuum leaks in the EGR system
  5. ECM software issues

Symptoms of P0408

  1. Check Engine Light illuminated on the dashboard
  2. Decreased fuel efficiency
  3. Rough idling or stalling
  4. Engine misfires
  5. Increased emissions

How to Fix P0408

  1. Begin by conducting a visual inspection of the EGR sensor 'B' and its wiring for any signs of damage or corrosion.
  2. Use a multimeter to test the voltage output of the EGR sensor 'B' while the engine is running to determine if it is within the specified range.
  3. Check for any obstructions or carbon buildup in the EGR system and clean or replace the EGR valve if necessary.
  4. Inspect the vacuum lines connected to the EGR system for leaks and repair or replace any damaged hoses.
  5. Clear the DTC using an OBD-II scanner and test drive the vehicle to ensure the issue has been resolved.

Cost to Fix P0408

The typical repair costs for addressing a P0408 code can vary depending on the specific cause of the issue. In general, replacing a faulty EGR sensor 'B' can cost between $150 to $300, including parts and labor. However, if additional components need to be replaced or if extensive diagnostic work is required, the total repair cost can increase. It is advisable to consult with a certified mechanic or auto repair shop to obtain a more accurate estimate based on your vehicle's make and model. Keep in mind that labor rates can vary, with hourly rates typically ranging from $80 to $150.

When is the Code Detected?

An improper voltage signal is sent to ECM through the valve

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Code P0408 Information for Specific Makes

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 P0408 Code

1. What are the common symptoms of OBDII code P0408?

- Common symptoms of P0408 may include engine stalling, rough idle, decreased fuel efficiency, and the illumination of the Check Engine Light.

2. What can cause the Exhaust Gas Recirculation (EGR) Sensor 'B' Circuit High fault code?

- The P0408 code is typically triggered by a faulty EGR position sensor, damaged wiring or connectors, or a malfunctioning EGR valve.

3. How can I diagnose the cause of P0408?

- To diagnose P0408, you can use an OBDII scanner to retrieve the fault code and then visually inspect the EGR system components for damage or corrosion. Testing the EGR sensor and related wiring may also be necessary.

4. Can a dirty EGR valve cause code P0408?

- Yes, a dirty or clogged EGR valve can disrupt the sensor readings and lead to the P0408 code being triggered. Regular maintenance can help prevent this issue.

5. What are the repair options for OBDII code P0408?

- Repair options for P0408 may include cleaning or replacing the EGR valve, testing and replacing the EGR sensor, repairing damaged wiring or connectors, and resetting the fault code with a scanner.

6. Will driving with code P0408 harm my vehicle?

- Driving with code P0408 may result in decreased engine performance and fuel efficiency. Continued driving with this fault unresolved can potentially cause damage to other engine components over time.

7. How urgent is it to address code P0408?

- While P0408 may not cause immediate harm to your vehicle, it is recommended to address the issue promptly to prevent further engine problems and ensure optimal performance.

8. Can I reset the Check Engine Light after fixing code P0408?

- Yes, once you have addressed the underlying cause of P0408, you can reset the Check Engine Light using an OBDII scanner to clear the fault code.

9. Is it possible to prevent OBDII code P0408 from recurring?

- Regular maintenance of the EGR system, including cleaning or replacing components as needed, can help prevent the recurrence of P0408. Keeping the system in good condition is key to avoiding this fault code.

10. Should I attempt to repair OBDII code P0408 myself?

- If you have experience with automotive repair and access to the necessary tools, you may be able to address P0408 yourself. However, if you are unsure or uncomfortable with the process, it is advisable to seek professional assistance to ensure the issue is properly diagnosed and resolved.

Discuss the causes and fixes for P0408 OBDII Code

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  • i have a 2004 f150 with a 4.2 with codes for missfire on #5 and #3 cyl and p0408 iv changed the coil , plugs and plug wires nothing has changed, it only misses somtimes usually around accelaration of about 2000 rpms and ltft for bank 2 is very high 23.99 , im going to check for vaccume leaks . any advice would help thanks . wally

    Reply to Comment

  • The P0408 code is for the EGR system. If the EGR got stuck open, it can cause an engine misfire.

    Reply to Comment

  • hello on VW 1.6tdi 2010 first the p046c00 fault code come up.
    I cleaned the egr complete and replaced the vacum regulator because it was not working. for 10km the car was working fine.After that the fault code p04800 always comes up and the car goes in limp mode...what could this be?

    Reply to Comment