P1404

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The VCM tests the EGR system during deceleration by momentarily commanding the EGR valve open. The pressure in the intake manifold increases when the EGR valve is open. The VCM monitors the Manifold Absolute Pressure (MAP) sensor signal during the EGR system diagnostic in order to determine the amount of EGR flow. The VCM calculates an error based on the difference between the actual MAP increase and a predetermined value. The VCM records the error and adjusts an internal fail counter towards the fail threshold if the error is too great. The VCM sets a DTC P0401 when the fail counter exceeds the fail threshold. The number of test samples required to exceed the fail threshold varies according to the magnitude of the detected flow errors.

The VCM allows only one EGR flow test sample to be taken during an ignition cycle. Following a scan tool Clear Info or a battery disconnect, the VCM allows twelve test samples during the first ignition cycle in order to aid in verifying a repair.

CONDITIONS FOR SETTING THE DTC

^ ECT is greater than 80°C and less than 120°C

^ IAT is less than 100°C

^ The Desired EGR Position is greater than 14 percent.

ACTION TAKEN WHEN THE DTC SETS

^ The Malfunction Indicator Lamp (MIL) will illuminate.

^ The PCM will record operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers 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 that is 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 the Desired EGR Positions on a cold vehicle with a scan tool, you can easily verify the fault. Check the freeze frame data in order 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 EGR system can control the EGR valve accurately and if the malfunction is present.

4. When the EGR valve electrical connector is disconnected, the scan tool should display the Actual EGR Position as 0%. If it does not, the malfunction lies either in the EGR signal circuit or the VCM.

6. If the EGR valve 5.0 volt reference is shorted to voltage, the DMM will read battery voltage and additional DTCs may be set.

11. A poor electrical connection may have caused this DTC to set. Be sure to check the terminals for being backed out, improperly formed, damaged, and for poor tension.

15. 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.

16. 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 as the old position was inaccurate due to the malfunction that caused the DTC. If the VCM sees an EGR command, the new minimum pintle position will not be learned.

17. If no malfunctions have been found at this point and no additional DTCs were set, refer to the Diagnostic Aids for additional checks and information.