Richard McCuistian, ASE Certified Master Automobile Technician

Technical Reviewer at

Written by Staff Writerns - Updated on September 23rd, 2021

Trouble codes are designed to provide a starting point for diagnosing problems that could increase vehicle emissions. Without them, it would be more difficult to figure out what’s going wrong with your car. Each code has a unique combination of letters and numbers.

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If you want to fix your car after finding out the code P0406 on your code reader or scanner, you have to know what it means, what are its causes and its symptoms.

What Does the P0406 Code Mean?

Diagnostic trouble code (DTC) P0406 stands for “Exhaust Gas Recirculation Sensor A Circuit High.” It means that the powertrain control module (PCM) perceives a high voltage signal from the exhaust gas recirculation (EGR) position sensor.

As its name implies, the EGR position sensor detects the position of the EGR valve. The PCM uses the sensor signal to monitor and adjust EGR valve operation.

The check engine code P0406 is triggered when the signal being sent back by the EGR position sensor to the PCM is higher than the specified range. The check engine light will activate as the PCM sets this code.

P0406 code is triggered when the signal being sent back by the EGR position sensor to the PCM is higher than the specified range.

If you’re planning a DIY approach to fix P0406, a technical understanding of the EGR system could help. You can read our advanced discussion here. If you have a Ford vehicle, additional reading about Delta Pressure Feedback EGR (DPFE) could also help. You can read our explanation here. Otherwise, continue below to quickly learn the possible causes of P0406.

Note: The definition of code P406 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What are the Possible Causes of the P0406 Code?

Here are the possible reasons why the sensor is sending too high voltage signals to the PCM:

Faulty EGR valve position sensorBad EGR valveCircuit issues, such as damaged wires or poor connectionsAn issue with the PCM, such as software in need of an update

What are the Common Symptoms of the P0406 Code?

The code P0406 can cause performance concerns. These problems can affect the driveability of your vehicle (but they usually won’t), but pay attention. Be ready to face some of these symptoms if you’ got a P0406 code on your OBD-II scan tool:

Failed emission test due to increased NOx emissionsDecreased engine performanceEngine pingingPoor fuel economyEngine stalling

How to Diagnose the P0406 Code

The information listed above contains the basics of the P0406 code. If you want to learn more about how to fix code P0406, you must first understand how to diagnose it. To get an idea of what the troubleshooting process might involve, just head on over to the videos linked below:

How to Fix the P0406 Code

The diagnostic and repair processes of the P0406 code may vary based on the vehicle’s make and model. Fixing this DTC is a task best left to the professionals if you are not that confident with your automotive know-how and DIY skills.

The first step to resolving the P0406 code is diagnosis. Pinpoint the underlying cause of the issue. Then, with the help of online auto repair resources and guides, figure out the correct way to fix the DTC. You can look up confirmed P0406 fixes and other useful information in a vehicle-specific factory repair subscription, such as ALLDATA.

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Products Mentioned in this Guide

EGR Valve
EGR Valve Position Sensor

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