Error P0404 – how to fix it?

Definition of the code P0404

Exhaust gas recirculation circuit Scope/performance

What does the P0404 code mean?

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

What causes the P0404 code?

• The ECM controls the EGR position with a sensor mounted on 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 a code.
• The EGR sensor exceeded the upper limits when the ECM ordered 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 memory.
• The engine may have pre-ignition when accelerating.
• The engine’s EGR system may cause the engine to fire, hesitate or even stop if it does not indicate the correct EGR valve position to the ECM.

How can a mechanic diagnose a P0404 code?

• Scan the codes and document the freeze frame data to verify the problem.
• Remove codes from engine and perform road tests to see if problem persists.
• Monitor the EGR sensor pid on the scanner to see if the sensor indicates that the valve is stuck open or not moving smoothly.
• Remove the EGR sensor and manually run the sensor to isolate the valve or sensor failure.
• Remove and inspect the EGR valve to see if it is carbonized, causing bad sensor readings.

The most common errors when diagnosing the P0404 code.

• Failure to manually operate the EGR position sensor to isolate the valve or sensor failure before replacing components.
• Failure to check wiring harness and connection to EGR position sensor for problems before replacing EGR position sensor or EGR valve.

How serious is the code P0404?

• The EGR system triggering this ECM code can disable the EGR system and render it inoperable.
• If the Check Engine light comes on, the vehicle will fail the emissions test.
• The position of the EGR is critical for the ECM to properly control the opening and closing of the EGR valve.

What repairs can fix code P0404?

1. If the EGR valve is partially open due to carbon buildup in the pin area and cannot be cleaned, replace it.
2. Replace the EGR position sensor if it is found to be unable to give a correct input reading to the ECM when moved manually.
3. Repair shorted or open wires to the EGR position sensor or connector.

Additional notes on code P0404

The P0404 code is triggered when the EGR position is not as expected by the ECM, and the most common cause is partial blockage of the EGR valve due to carbon deposits on the valve stub.