Purpose
The Exhaust Gas Recirculation (EGR) system is used to lower the oxides
of nitrogen (NOx) emission levels that are caused by high combustion temperatures.
The EGR does this by decreasing combustion temperature.
The main element of the system is the linear EGR valve. The EGR valve
feeds small amounts of exhaust gas back into the combustion chamber. When
the exhaust gases dilute the fuel-to-air mixture, combustion temperatures
are reduced.
Operation
The linear EGR valve is supplies the EGR to the engine independent
of the intake manifold vacuum. The valve controls the EGR flow from the exhaust
to the intake manifold through an orifice with a PCM-controlled pintle.
During operation, the PCM controls the pintle position by monitoring the
pintle position feedback signal. The feedback signal can be monitored with
the scan tool Actual EGR Pos. The Actual EGR Pos should always similar to
the commanded EGR position (Desired EGR Pos). The PCM uses information from
the following sensors in order to control the pintle position:
| • | The engine Coolant Temperature (ECT) sensor |
| • | The throttle Position (TP) sensor |
| • | The Mass Airflow (MAF). |
The linear EGR valve is usually activated during the following
conditions:
