P0401

Diagnostic Chart:

Wiring Diagram:

The linear EGR system consists of a linear EGR valve, the PCM and its associated wiring. The PCM directly controls the ground for the EGR valve when certain conditions have been met. Voltage is supplied by the Under Hood Junction Block (UHJB) to the EGR valve when the ignition is turned On. When the PCM grounds the valve, a diagnostic feedback signal can determine if the valve had actually moved. Since the correct feedback voltage is possible, but the passage has restricted flow, P0401 was implemented.

DTC PARAMETERS

EGR flow restrictions are diagnosed during a deceleration. The EGR valve is commanded closed during a normal deceleration. To run the P0401 test the valve is opened during deceleration and a change in MAP is expected. If the change is MAP is below a threshold it indicates flow is restricted.

DTC P0401 will set if a calculated value compared to an engine speed vs barometric pressure determines there is a restriction in EGR flow when:

^ Engine speed is between 1350-2000 rpm.

^ VSS is greater than 48 km/h (30 mph).

^ Throttle is closed.

^ ECT is greater than 70°C (150°F).

^ Vehicle is in top gear.

^ No EGR pintle, TP, MAF, VSS, IAT, ECT or IAC DTCs have been set.

NOTE: The EGR flow insufficient test is checked once per ignition cycle during deceleration.

DIAGNOSTIC AIDS

When attempting to diagnose an intermittent problem use the Scan tool to review malfunction history diagnostic information. The supplemental data can be used to duplicate a problem.

The Scan tool can read the number of deceleration test that have been performed since the DTCs were cleared. The Scan tool also displays the EGR decel average value as well as the fail threshold when the DTC will set. The average must be greater than the threshold to set P0401.

Check the tightness of the female terminal grip with a spare male terminal.

^ B+ is supplied to the E terminal on the EGR valve when the ignition is On.

^ Carbon buildup around the pintle valve may restrict exhaust gas flow.

^ Diagnose the other DTCs listed under parameters, especially a MAP sensor DTC before diagnosing P0401.