P0405

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 Powertrain Control Module (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 desired EGR position.

The PCM monitors the position of the EGR valve through a feedback signal. The PCM supplies a 5-volt reference circuit and a ground circuit to the EGR valve. A voltage signal representing the EGR valve pintle position is sent to the PCM 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 be near the desired EGR position.

CONDITIONS FOR RUNNING THE DTC
^ The ignition voltage is more than 11.7 volts.
^ The engine is running.

CONDITIONS FOR SETTING THE DTC
^ The EGR feedback signal voltage is less than 0.14 volts.
^ All conditions are present for 5 seconds.

DIAGNOSTIC AIDS
^ Poor connection at the PCM or EGR valve-Inspect the harness connectors for:
- Backed out terminals
- Improper mating
- Broken locks
- Improperly formed or damaged terminals
- Poor terminal to wire connection
^ Refer to Connector Repairs in Diagrams.
^ Damaged harness-Inspect the wiring harness for damage. If the harness appears to be OK, connect a DMM and check the circuit continuity while moving connectors and wiring harnesses related to the EGR valve. A change in the DMM display will indicate the location of the malfunction. Refer to Connector Repairs in Diagrams.

TEST DESCRIPTION

Steps 1-3:

Steps 4-15:

The number below refers to the step number on the diagnostic table.
2. This step verifies that the malfunction is present.