Exhaust Gas Recirculation (EGR) System Description. Buick Lucerne 2008

For 1990-2009 cars only

Makes 🢒 Buick 🢒 2008 🢒 Lucerne 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Exhaust Gas Recirculation (EGR) System Description

Exhaust Gas Recirculation (EGR) System

The exhaust gas recirculation (EGR) system is used to reduce the amount of nitrogen oxide (NOx) emission levels caused by combustion temperatures exceeding 816°C (1,500°F). It does this by introducing small amounts of exhaust gas back into the combustion chamber. The exhaust gas absorbs a portion of the thermal energy produced by the combustion process and thus decreases combustion temperature. The EGR system will only operate under specific temperature, barometric pressure and engine load conditions in order to prevent driveability concerns and to increase engine performance.

Linear EGR Valve


(1)	Cap-Sensor
(2)	Sensor-EGR Pintle Position
(3)	Pole Piece-Primary
(4)	Bobbin and Coil Assembly
(5)	Sleeve-Armature
(6)	Valve-Pintle
(7)	Armature and Base Assembly

Linear EGR Control

The linear EGR valve is controlled by a high side driver within the engine control module (ECM). The high side driver provides 12 volts that is pulse width modulated (PWM) by a duty cycle via the high control circuit of the EGR valve . The ground path is provided by the low control circuit of the EGR valve. The ECM calculates the amount of EGR needed based on the following inputs:

•	The engine coolant temperature (ECT) sensor

•	The intake air temperature (IAT) sensor

•	The barometric pressure (BARO)

•	The manifold absolute pressure (MAP) sensor

•	The throttle position (TP) sensor

•	The mass air flow (MAF) sensor

EGR Diagnostics

The engine control module (ECM) tests the EGR flow during deceleration by momentarily commanding the EGR valve to open while monitoring the signal of the manifold absolute pressure (MAP) sensor. When the EGR valve is opened, the ECM will expect to see a predetermined increase in MAP. If the expected increase in MAP is not detected, the ECM records the amount of MAP difference that was detected and adjusts a calibrated fail counter towards a calibrated fail threshold level. When the fail counter exceeds the fail threshold level, the ECM will set a diagnostic trouble code (DTC).

Normally, the ECM will only allow one EGR Flow Test Count during an ignition cycle. To aid in verifying a repair, the ECM allows twelve EGR Flow Test Counts during the first ignition cycle following a code clear or a battery disconnect. Between nine and twelve EGR Flow Test Counts should be sufficient for the ECM to determine adequate EGR flow and pass the EGR flow test. If the ECM detects an EGR flow error, a DTC will set.

The ECM monitors the position of the EGR valve pintle via the EGR position sensor. If the ECM detects a calibrated variance between the Desired EGR Position parameter and the EGR Position Sensor parameter, actual position, for a calibrated amount of time a DTC will set.

The ECM also monitors the EGR solenoid high control circuit EGR solenoid low control circuit for electrical faults. If an EGR control circuit fault is detected for a calibrated amount of time a DTC will set.