The EGR valve is located atop the intake manifold in a port that is machined into the manifold (figure 5-50). A vacuum-operated pintle in the valve controls the amount of exhaust gas that is recirculated into the intake manifold.
Recirculating these gases helps reduce emissions. A normally open EGR solenoid controls the EGR valve. The solenoid allows vacuum to pass to the EGR. An EGR vent solenoid is used to vent pressure from the EGR valve chamber during non-EGR conditions.
EGR Circuit Operation
The PCM provides a ground path to the EGR solenoid on CKT 435 that allows the solenoid to control the EGR valve (figure 5-51). The PCM also energizes the EGR vent solenoid through CKT 971. Both solenoids receive battery power through the ignition switch on CKT 539. During normal operation, the PCM compares the EGR duty cycle command with the EGR pressure control/baro sensor signal it receives on CKT 433. If there is a difference between PCM-command EGR and actual EGR position, the PCM makes minor adjustments in the duty cycle to correct the difference. If the difference is too great for the PCM to compensate, a DTC may set.
DTC 32 — “EGR Circuit Error”
DTC 32 sets when engine RPM is greater than 506, there is a 50 kPa difference between desired EGR and actual EGR for more than 25.5 seconds, and there is no DTC 31 or 33. A DTC 32 will prompt the PCM to shut down the EGR system.
DTC 44 — “EGR Pulse Width Error”
DTC 44 sets when the PCM doesn’t see ignition voltage at terminal E15 when the EGR solenoid is commanded “OFF.”
DTC 45 — “EGR Vent Error”
DTC 45 sets when the PCM doesn’t see ignition voltage at terminal A4 when EGR vent is commanded “OFF.”