P0404

Diagnostic Chart:

Wiring Diagram:

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 feeding 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 exhaust flow into the intake manifold from the exhaust manifold through an orifice with a VCM controlled pintle. The VCM controls the pintle position using inputs from the Throttle Position (TP) sensor and the Manifold Absolute Pressure (MAP) sensor. The VCM 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 DESIRED EGR POSITION.

The VCM monitors the position of the EGR valve through a feedback signal. The VCM supplies a 5.0 volt reference and a ground to the EGR valve. A voltage signal representing the EGR valve pintle position is sent to the VCM from the EGR valve. This feedback signal can also be monitored on a scan tool and is the actual position of the EGR pintle. The ACTUAL EGR POSITION should always be near the commanded or DESIRED EGR POSITION.

CONDITIONS FOR SETTING THE DTC

^ No MAP DTCs

^ No IAT DTCs

^ No ECT DTCs

^ No TP DTCs

^ P0300, P1336, or P1404 have not set

^ No EVAP DTCs

^ No IAC DTCs

^ Ignition voltage is greater than 11.7V.

^ EGR commanded ON (DESIRED EGR POSITION is greater than 0%).

^ ACTUAL EGR POSITION differs from DESIRED EGR POSITION by more than 9% for 18 seconds.

ACTION TAKEN WHEN THE DTC SETS

^ The Malfunction Indicator Lamp (MIL) will illuminate.

^ The VCM will record operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records will store this information.

^ A history DTC is stored

^ The EGR Valve is disabled.

CONDITIONS FOR CLEARING THE MIL/DTC

^ The VCM turns the MIL OFF after 3 consecutive drive trips when the test has Run and Passed and not Failed.

^ A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle).

^ Use the scan tool Clear Information function.

^ Disconnect the VCM battery feed for 30 seconds.

DIAGNOSTIC AIDS

Due to the moisture associated with exhaust systems, the EGR valve may freeze and stick in colder weather at times. After the vehicle is brought into a warm shop for repairs, the valve warms and the problem disappears. By watching the Actual EGR and Desired EGR Positions on a cold vehicle with a scan tool, the fault can be verified easily. Check the freeze frame data to determine if the DTC set when the vehicle was cold by viewing the Engine Coolant Temperature (ECT).

TEST DESCRIPTION

Number(s) below refer to the step number(s) on the Diagnostic Table.

2. Commanding the EGR valve open determines whether the VCM can control the EGR valve accurately and if the malfunction is present.

4. A test light will glow dimly when the EGR valve is commanded to 20%, and brighter as the EGR valve is commanded to 100%.

12. If the EGR valve 5 volt reference is shorted to voltage, the DMM will read battery voltage and additional DTCs may be set.

15. A problem may exist within the terminals which would not show up in probe type testing. Be sure to check the terminals for being backed out, improperly formed, or damaged.

21. The replacement VCM must be programmed and the Crankshaft Position System Variation Learn Procedure must be performed. Refer to the latest Techline procedures for VCM programming.

22. Clearing the DTCs is a very important step for this diagnostic. The clearing function allows the EGR valve to relearn a new minimum pintle position.