EGR System - Diesel: 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.