Exhaust Gas Recirculation: Description and Operation

DESCRIPTION
The EGR system is designed to lower NOx (oxides of nitrogen) emission levels created by high combustion temperatures. The main element of the system is an EGR valve. The EGR valve opens in one of two ways, vacuum or electrical depending on which valve or control system is being used. On vehicles equipped with California emissions, a linear EGR valve and a canister purge solenoid are used in most applications.

OPERATION
The EGR valve will open when conditions of operation have been met. The valve will open and allow exhaust gasses to reenter the combustion chamber. When too much exhaust gas is allowed to enter the chamber, proper combustion will not occur. For this reason only very little exhaust gas is allowed to re-enter the combustion chamber.

NOTE: When performing an inspection of the EGR system, Do Not connect exhausting shop air to the tailpipe of the vehicle. The vacuum created by the shop air could cause false EGR valve operation to occur.

EGR VALVES AND CONTROLLERS
There are three types of EGR valves used based on engine and emissions package. Verify which system your vehicle is equipped with before performing diagnostics. Refer to EGR Valve / Application and ID.