P0401

DTC P0401 Exhaust Gas Recirculation (EGR) Insufficient Flow Detected:

Exhaust Gas Recirculation (EGR):

CIRCUIT DESCRIPTION
The Vehicle Control Module-A (VCM-A) tests the exhaust gas recirculation valve by momentarily commanding the valve "ON" while monitoring Manifold Absolute Pressure (MAP). If the expected MAP increase is not seen under certain operating conditions (decel) for a calibrated number of tests, the VCM-A will turn "ON" the Malfunction Indicator Lamp (MIL) (Service Engine Soon) and store DTC P0401. DTC P0401 is a type "A" DTC.

DTC P0401 WILL SET WHEN
^ No Throttle Position (TP) sensor DTCs set.
^ No Manifold Absolute Pressure (MAP) DTCs set.
^ No Vehicle Speed Sensor (VSS) DTCs set.
^ No Intake Air Temperature (IAT) sensor DTCs set.
^ No Engine Coolant Temperature (ECT) sensor DTCs set.
^ No Idle Air Control (IAC) DTCs set.
^ No linear Exhaust Gas Recirculation (EGR) Pintle Position DTCs set.
^ No Transmission DTCs set.
^ No Misfire DTCs set.
^ No Heating Ventilation Air Conditioning (HVAC) DTCs set.
^ Change in (IAC) is less than 3 counts.
^ ECT is greater than 78°C (172°F).
^ Barometric Absolute Pressure (BARO) is greater than 70 kPa (21 Hg).
^ Vehicle speed is greater than 30 mph.
^ AC clutch status is unchanged.
^ Transmission is in locked or unlocked stage (stable).
^ Engine speed is between 1000 RPM and 1600 RPM.
^ The EGR flow test will be failed and DTC P0401 set if the VCM-A does not detect a sufficient rise in MAP during above conditions.

ACTION TAKEN (VCM-A WILL DEFAULT TO)
With a current DTC P0401 set, the VCM-A will turn "ON" the MIL (Service Engine Soon).

DTC P0401 WILL CLEAR WHEN
The VCM-A will turn the MIL "OFF" after three consecutive trips without a fault condition present. A history DTC will be cleared if no fault conditions have been detected for forty warm-up cycles [coolant temperature has risen 22°C (40°F) from start-up coolant temperature and engine coolant temperature exceeds 71°C (160°F) that same ignition cycle] or the Tech 1 clearing feature has been used.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Ensures that the EGR valve is allowing EGR flow and the VCM-A is capable of controlling the EGR valve.
2. Ensures that CKT 433 is not shorted to ground.
3. Ensures that CKT 433 is not open and that the VCM-A quad-driver for CKT 435 is functioning properly.

DIAGNOSTIC AIDS
An intermittent may be caused by a wire broken inside the insulation.

Check for:
^ Poor connection or damaged harness - Inspect VCM-A harness connectors for backed out terminal "BL18", improper mating, broken locks, improperly formed or damaged terminal, poor terminal to wire connection and damaged harness.
^ Intermittent test - If connections and harness check OK, monitor a digital voltmeter connected between terminal "BL18" and ground while moving related connectors and wiring harness. If the failure is induced, the voltage reading will change.

NOTE: If the EGR valve shows signs of excessive heat, check the exhaust system for blockage (possibly a plugged converter) using the procedure found on restricted exhaust system check. If the exhaust system is restricted, repair the cause; one of which might be an injector which is open due to one of the following:
A. Stuck.
B. Grounded driver circuit.
C. Possible faulty VCM-A.

If this condition is found, the oil should be checked for possible fuel contamination.