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Home >> Saturn >> 1996 >> SC2 Automatic, MP6 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Diagnostic Trouble Codes >> DTC P0401 - EGR System Insufficient Flow >> Circuit Description

Circuit Description

PCM directly controls the ground for the linear EGR valve when certain conditions have been met. Voltage is supplied by the underhood fuse/relay block to the EGR valve when ignition is turned on. When PCM grounds the valve, a diagnostic feedback signal can determine is valve had actually moved.

EGR flow restrictions are diagnosed during a deceleration. EGR valve is commanded closed during normal deceleration and a change in MAP is expected. If the change in MAP is less than a threshold, a restricted flow is indicated.

DTC will set if calculated value compared to an engine speed barometric pressure determines that there is restriction in EGR flow when engine speed is between 1350-2000 RPM, VSS is greater than 30 MPH, throttle is closed, coolant temperature is greater than 150°F (70°C), vehicle in top gear and no EGR, TP sensor, MAP, VSS, IAT, ECT or IAC DTCs have been set. EGR flow insufficient test is checked once per ignition cycle during deceleration.

NOTE: If DTC P1406 is present, diagnose this DTC first.
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