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P0405 OBD-II Trouble Code: Exhaust Gas Recirculation Sensor Circuit A Low

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P0405 code definition

Exhaust Gas Recirculation Sensor Circuit A Low

What the P0405 code means

P0405 is an OBD-II generic code that the engine control module (ECM) detected the engine exhaust gas recirculation (EGR) sensor has went below its specification range. A short to ground of the sensor input to the ECM.

What causes the P0405 code?

  • The ECM monitors the EGR position sensor any time the key is on and if the sensor input signal voltage drops below a specified voltage returning to the ECM, then the code is set.

  • The EGR sensor return is internally shorted to ground.

  • The EGR sensor return wiring or connection is shorted to ground.

  • The EGR sensor 5 volt reference voltage is open in the sensor or connection is not making contact.

What are the symptoms of the P0405 code?

  • The Check Engine Light will be illuminated and the code is set in ECM memory.

  • The ECM may open the EGR valve more than needed if voltage is too low causing a stall or hesitation on acceleration.

  • The engine EGR system can cause the engine to run rough, hesitate, or even stall if it is not indicating the proper EGR valve position to the ECM.

  • The ECM may disable the valve from opening when it sees a fault and the engine may have pre-ignition on acceleration.

How does a mechanic diagnose the P0405 code?

  • Scans codes and documents the freeze frame data in order to verify the problem
  • Clears the engine codes and road tests to verify concern and codes comes back
  • Monitors the EGR sensor pid on a scanner to see if the sensor indicates the valve is in the correct closed position or the sensor voltage return is below specifications
  • Removes the EGR sensor connector and checks for corrosion in connector and cleans if needed
  • Checks the connector if the 5 volts reference is getting to the sensor connection
  • Connects the sensor reference voltage and signal return pins together and checks the scanner to show reference voltage on EGR sensor pid
  • Replaces the EGR sensor or repairs wiring as needed then rechecks system for proper readings

Common mistakes when diagnosing the P0405 code

  • Not connecting the sensor reference voltage and signal return pins together to see if all the wiring is good before replacing the EGR position sensor

  • Not checking the wiring harness and connection to the EGR position sensor for shorts or open circuits before replacing the EGR position sensor

How serious is the P0405 code?

  • The ECM may disable the EGR system and render it inoperative when this code is active.

  • The Check Engine Light being on causes the vehicle to fail emission testing.

  • The EGR position is critical for the ECM to properly control the EGR valve opening and closing, and can cause the engine to run rough and stall.

What repairs can fix the P0405 code?

  • Replacing the EGR position sensor after the wiring is checked to be okay
  • Repairing the wiring short to the EGR position sensor or connector signal return
  • Repairing an open in the voltage reference to the EGR sensor

Additional comments for consideration regarding the P0405 code

Code P0405 is triggered when the EGR position is below the ECM expected sensor position and the most common cause is the EGR sensor has an open circuit internally.

Need help with a P0405 code?

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