P0405

Circuit Description
An Exhaust Gas Recirculation (EGR) system is used to lower Oxides of Nitrogen (NOx) emission levels caused by high combustion temperatures. It accomplishes this by feeding small amounts of exhaust gases back into the combustion chamber. When the air/fuel mixture is diluted with the exhaust gases combustion temperatures are reduced.

A linear EGR valve is used on this system. The linear EGR valve is designed to accurately supply exhaust gases to the engine without the use of intake manifold vacuum. The valve controls exhaust flow going into the intake manifold from the exhaust manifold through an orifice with a Control Module (PCM/VCM) controlled pintle valve. The Control Module commands the EGR by applying a 12 volt duty cycle to the EGR valve. This can be monitored on a scan tool as Desired EGR position.

The Control Module can monitor the pintle position with the EGR pintle position signal. This sensor uses a variable resistor with a 5 volt reference, a signal circuit and a ground. The signal circuit monitors changes in voltage on the variable resistor as the pintle moves.

The VCM will set a DTC P0405 if an unusually low pintle position signal voltage is detected for a calibrated period of time.

Conditions for Running the DTC
The ignition voltage is more than 5 volts to enable the diagnostic or less than 4 volts to disable the diagnostic.

Conditions for Setting the DTC
The EGR feedback signal voltage is less than 0.12 volts for more than 10 seconds.

Action Taken When the DTC Sets
^ The Control Module illuminates the Malfunction Indicator Lamp (MIL) if a failure is detected during 2 consecutive key cycles.
^ The Control Module will set the DTC and records the operating conditions at the time the diagnostic fails. The Control Module stores the failure information in the scan tools Freeze Frame and/or the Failure Records.

Conditions for Clearing the MIL/DTC
^ The Control Module turns OFF the MIL after 3 consecutive drive trips when the test has Run and Passed.
^ 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 start-up coolant temperature and the Engine Coolant Temperature is more than 70°C (158°F) during the same ignition cycle).
^ Use the scan tool Clear Information function.

Diagnostic Aids
Be sure to check for intermittents.
An intermittent may be caused by any of the following conditions:
^ A poor connection
^ Rubbed through wire insulation
^ A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
3. Commanding the EGR valve open determines whether the EGR system can control the EGR valve accurately and if the condition is present.
6. Jumping the 5 volt reference circuit to the signal circuit checks the signal circuit and VCM.
9. The 5 volt reference of the VCM supply is shared by the MAP, TP, FTP and EGR sensors. A short in any of the sensors' 5 volt reference circuits or an internally shorted sensor will cause this DTC to set.
11. A 5 volt reference circuit short to the EGR valve feed control circuit will ground through the EGR valve when the EGR valve harness connector is connected.
19. Check the terminals for being backed out, improperly formed, damaged and for poor tension.
20. 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.
21. 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.