Exhaust Gas Recirculation: Description and Operation

Linear EGR Valve Operation:

Linear EGR Valve - Cross Sectional View:

DESCRIPTION
The Exhaust Gas Recirculation (EGR) system is used to lower NOx (Oxides of Nitrogen) emission levels caused by high combustion temperature and excessive oxygen. It does this by decreasing combustion temperature and displacing oxygen.

The main element of the system is the EGR valve which is mounted to the right lower front of the engine.

The EGR valve feeds small amounts of exhaust gas back into the combustion chamber as shown in the image.

The EGR valve is controlled by the ECM, to let exhaust flow into the plenum. The exhaust gas then moves with the air/fuel mixture into the combustion chamber. If too much exhaust gas enters, combustion will not occur. For this reason, very little exhaust gas is allowed to pass through the valve. The EGR valve is usually open during warm engine operation and when the vehicle is above idle speed.

EGR CONTROL
The linear EGR valve contains a solenoid that directly actuates the valve's pintle to open against a normally closed spring. The pintle position of the EGR valve is controllable since the valve provides pintle position sensor feedback to the ECM. Pintle position is controlled by the ECM through the EGR interface module. The ECM determines when EGR is enabled based on various engine parameters:

- Throttle Position (TP) sensor.
- Engine Coolant Temperature (ECT) sensor.
- Engine speed (RPM).
- Vehicle Speed Sensor (VSS).
- Manifold Absolute Pressure (MAP).

Based on all these inputs, the ECM will determine the proper amount of exhaust gas recirculation necessary to lower combustion temperatures.

Positioned at top of the linear EGR assembly are 5 terminals:

A. The pulse width modulated signal from the EGR valve signal modifier module.
B. Ground circuit.
C. EGR position signal.
D. 5 volt reference.
E. 12 volt supply.