DESCRIPTION
Purpose of the Exhaust Gas Recirculation (EGR) system is to limit formation of oxides of nitrogen (NOx) emissions. This is done by reducing high peak combustion temperatures at which NOx is formed. By reintroducing a small amount of exhaust gas back into the combustion chamber, high temperatures are avoided and thus NOx emissions formation is reduced.
EGR system consists of EGR valve, exhaust pressure regulator valve (EPR), EGR/EPR solenoid assembly, manifold absolute pressure (MAP) sensor, throttle position switch (TPS) and vacuum pump.
OPERATION
The ECM controls EGR by controlling the amount of "on" and "off" time of EGR solenoid through input from engine speed sensor and TPS. To monitor ECM control of EGR, a MAP sensor is used to measure the amount of absolute pressure in EGR vacuum line. If a minor variation between calculated EGR and actual EGR is monitored by the ECM, the ECM will make a correction. If variation is too great for ECM to correct, an error is detected. ECM will go into default.
When ECM monitors EGR is not needed, the EGR vent solenoid operates to vent vacuum. The ECM also energizes EPR solenoid to close EPR valve at idle to lower exhaust backpressure.
Scheme 197
Scheme 198
SYSTEM TESTING
Note. Testing information not available.