Error P0404 – how to fix?

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Code Definition P0404

Exhaust Gas Recirculation Circuit Range / Performance

What does the code P0404 mean?

P0404 is a generic OBD-II code which indicates that the engine control module (ECM) has detected that the engine exhaust gas recirculation (EGR) valve or sensor is out of specification or that its performance is out of specification.

What causes the P0404 code?

  • The ECM monitors the EGR position with a sensor mounted on the top of the EGR valve and the valve was out of position when the EGR was commanded to close.
  • The movement of the EGR valve must be smooth, without jerking, otherwise the ECM sets the code.
  • The EGR sensor exceeded its high limits when the ECM commanded the EGR to open.

What are the symptoms of the P0404 code?

  • The Check Engine light will come on and the code will be stored in the ECM’s memory.
  • The engine may preign when accelerating.
  • The engine EGR system can cause the engine to misfire, rock or even stall if it does not correctly position the EGR valve to the ECM.

How can a mechanic diagnose the P0404 code?

  • Scan the codes and document the data from the frozen frame to verify the problem.
  • Removes codes from the engine and runs road tests to see if the problem recurs.
  • Monitor the pid of the EGR sensor on a scanner to see if the sensor indicates that the valve is stuck open or not moving smoothly.
  • Remove the EGR sensor and manually trigger the sensor to isolate the valve or sensor failure.
  • Remove and inspect the EGR valve to see if it is charred, causing bad sensor readings.

The most common errors when diagnosing the P0404 code

  • No manual operation of the EGR position sensor to isolate the valve or sensor failure before replacing components.
  • Failure to check the wiring harness and connection to the EGR position sensor for problems before replacing the EGR position sensor or EGR valve.

How serious is the P0404 code?

  • An EGR system that triggers this ECM code may disable the EGR system and render it inoperable.
  • Illumination of the Check Engine light causes the vehicle to fail the Emission Test.
  • The EGR position is critical to the ECM to properly control the opening and closing of the EGR valve.

What repairs can fix the code P0404?

  1. If the EGR valve is partially open due to carbon build-up in the pin area and cannot be cleaned, replace it.
  2. Replace the EGR position sensor if it is found that it is unable to give a valid input to the ECM during manual shifting.
  3. Repair the shorted or open wires to the EGR position sensor or connector.

Additional notes regarding code P0404

Code P0404 triggers when the EGR position is not as expected by the ECM and the most common cause is a partial obstruction of the EGR valve due to carbon build-up on the valve plug.

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