EGR System - Diesel: Operation
The ECM controls EGR by controlling amount of "on" and "off" time of EGR solenoid using input from engine speed sensor and TPS. The ECM uses input from the MAP sensor to measure amount of absolute pressure in EGR vacuum line. If a minor variation between calculated EGR and actual EGR is monitored by ECM, the ECM will make a correction. If variation is too great for ECM to correct, an error is detected. The ECM will go then into default.
When EGR is not needed, the EGR vent solenoid is energized by the ECM to vent vacuum. The ECM also energizes EPR solenoid to close EPR valve at idle to lower exhaust backpressure.