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P0409 OBD-II Trouble Code: Exhaust Gas Recirculation Sensor "A" Circuit

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P0409 code definition

P0409 is a generic OBD2 diagnostic trouble code pointing to an issue with the exhaust gas recirculation circuit. This code may be seen with other EGR codes.

What the P0409 code means

The P0409 code is set when there is a malfunction in the exhaust gas recirculation sensor A circuit. Low voltage from sensor A is detected by the ECU. This causes a Check Engine Light to be shown on the dashboard.

What causes the P0409 code?

  • Faulty EGR valve
  • Open or short in the wiring harness
  • Carbon Buildup on EGR valve
  • Failed EGR solenoid or position sensor

What are the symptoms of the P0409 code?

P0409 has a few typical symptoms. In all cases the Check Engine Light will be seen on the dashboard. The vehicle may experience a lack of power and a ping noise under heavy use. In some cases no adverse symptoms are noticed other than the Check Engine Light.

How does a mechanic diagnose the P0409 code?

  • Hooks up a scan tool tool to the DLC port on the vehicle and checks for any history, pending, or current codes.

  • Checks the freeze frame data which tells the technician under what conditions the DTC was set under

  • Clears the codes and takes the vehicle on a test drive under similar circumstances as the freeze frame data

  • Performs a visual inspection on the EGR valve, wiring, and vacuum lines.

  • Uses a scan tool to check EGR operation

  • Inspects the EGR for any carbon buildup or a stuck valve

Common mistakes when diagnosing the P0409 code

Mistakes are seen when steps are overlooked or not completed in the proper order. This can cause the replacement of parts that work fine wasting time and money.

How serious is the P0409 code?

The P0409 can be a minor annoyance but should not prevent the vehicle from being driven to a safe location once the code is seen. The EGR system is used to recycle exhaust gases back into the intake to help with emissions and will prevent the passing of OBD2 emissions while P0409 is present.

What repairs can fix the P0409 code?

  • Replacing the EGR valve
  • Decarbonizing the EGR valve
  • Repairing or replacing the wiring harness
  • Replacing the EGR solenoid
  • Replacing the EGR position sensor

Additional comments for consideration regarding the P0409 code

In cases where the EGR valve is stuck open or closed with carbon buildup this can be removed with cleaners which will fix the problem in some cases. A throttle body cleaner can be used to remove the carbon buildup and restore EGR valve operation.

Need help with a P0409 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
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