P0404

Circuit Description
An Exhaust Gas Recirculation (EGR) system is used in order to lower Oxides of Nitrogen (NOx) emission levels. The EGR system accomplishes this by recirculating small amounts of exhaust gas back into the combustion chamber. High combustion temperatures cause NOx. Combustion temperatures are reduced when the air/fuel mixture is diluted with the exhaust gases.
The EGR valve is designed to accurately supply exhaust gases to the engine without the use of intake manifold vacuum. The EGR valve controls the exhaust flow into the intake manifold from the exhaust manifold through an orifice with a PCM controlled pintle. The PCM controls the pintle position using inputs from the Throttle Position (TP) sensor, the Manifold Absolute Pressure (MAP) sensor and, the Engine Coolant Temperature (ECT) sensor. The PCM commands the EGR valve in order to supply the correct amount of exhaust gas recirculation for the current engine operating conditions. This can be monitored on a scan tool as the Commanded EGR Position.
The ability of the PCM to control the EGR valve is verified with this test. The PCM calculates an error based on the difference between the actual EGR position and the commanded EGR position. The PCM sets this DTC if the error is too great.

Conditions for Running the DTC
^ The ignition voltage is greater than 11.7 volts.
^ The commanded EGR position is greater than 0%.
^ The EGR flow test is not active.

Conditions for Setting the DTC
The difference between the commanded EGR position and the actual EGR position is greater than 10%.
The failure counter is greater than a predetermined value.

Action Taken When the DTC Sets
^ The PCM illuminates the Malfunction Indicator Lamp on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure records.
^ The PCM disables the EGR for the ignition cycle.

Conditions for Clearing the MIL/DTC
^ The PCM turns the MIL OFF after three consecutive ignition cycles that the diagnostic runs and does not fail.
^ A last test failed (current DTC) clears when the diagnostic runs and does not fail.
^ A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
^ Use a scan tool in order to clear the MIL/DTC.

Diagnostic Aids

Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

The following may cause an intermittent:
^ Poor connections.
^ Corrosion.
^ Mis-routed harness.
^ Rubbed through wire insulation.
^ Broken wire inside the insulation.
Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can aid in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also aid determining how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This will isolate when the DTC failed. For an intermittent condition, refer to Symptoms. Symptom Related Diagnostic Procedures

Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
2. This step determines if the EGR valve can be commanded open.
3. Excessive resistance in the EGR control circuit or the EGR ground circuit will result in the EGR not responding correctly to the commanded EGR position.
4. Inspect the PCM connector for poor connections. Refer to Intermittents and Poor Connections Diagnosis.
5. Inspect the PCM connector for poor connections. Refer to Intermittents and Poor Connections Diagnosis.
6. Excessive resistance in the control circuit or the ground circuit will cause this DTC to set. With the EGR commanded to 100% the test lamp should light with full intensity. Connect the test lamp across the battery terminals and compare the test lamp intensity to the EGR control circuit intensity.