P0401

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) tests the Exhaust Gas Recirculation (EGR) system during deceleration by momentarily commanding the EGR valve to open while monitoring the Manifold Absolute Pressure (MAP) sensor signal. When the EGR valve is opened, the PCM should see a proportional increase in MAP. If the expected increase in MAP is not seen, the PCM notes the amount of error that was detected and adjusts an internal fail counter towards a fail threshold level. When the fail counter exceeds the fail threshold level, the PCM will set Diagnostic Trouble Code (DTC) P0401. The number of test samples required to accomplish this may vary according to the amount of detected flow error.

Normally, the PCM will only allow one EGR flow test sample to be taken during an ignition cycle. To aid in verifying a repair, the PCM allows fifteen test samples during the first ignition cycle following a scan tool Clear Info or a battery disconnect. Between five and fifteen samples should be sufficient for the PCM to determine adequate EGR flow and pass the EGR test.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0201-P0208, P0300, P0335, P0336, P0385, P0386, P0405, P0449, P0502, P0503, P0506, or P0507 are not set.
^ The system voltage is between 11-18 volts.
^ The AC status does not change.
^ The transaxle range does not change.
^ The Throttle Position (TP) angle is less than 1.19 percent, deceleration.
^ The Deceleration Fuel Cut-off (DFCO) is steady for 0.3 second.
^ The Engine Coolant Temperature (ECT) is between 80-110°C (176-230°F).
^ The engine speed is between 700-1,200 RPM.
^ The Idle Air Control (IAC) position is steady greater than 8 counts.
^ The Manifold Absolute Pressure (MAP) is steady between 15-70 kPa.
^ The vehicle speed is more than 62.5 km/h (37 mph) during deceleration.
^ The Barometric Pressure (BARO) sensor is more than 70 kPa.
^ The vehicle will need to be driven above 84.5km/h (50 mph), and then allowed to decelerate. When the vehicle is decelerating while meeting all of the criteria listed above, the PCM will enable the test to run. As the test is running, you will see the Desired EGR parameter and the EGR position sensor on the scan tool change from 0 to a calibrated value above 0.

CONDITIONS FOR SETTING THE DTC
The MAP changes monitored during EGR flow test indicate an insufficient EGR flow.

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the Malfunction Indicator Lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
^ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
^ Use a scan tool in order to clear the MIL and the DTC.

DIAGNOSTIC AIDS

IMPORTANT: Inspect for the following conditions:
^ An EGR valve that shows signs of excessive heat-Check the exhaust system for blockage or for a plugged catalytic converter. Refer to the Restricted Exhaust. Restricted Exhaust
^ A vacuum restriction to the MAP sensor-A restriction to the MAP sensor can cause the EGR flow test to fail due to insufficient MAP changes being monitored during the test.
^ An engine that is running poorly may cause this DTC to set.
^ A poor connection or damaged harness-Inspect the wiring harness for damage.
^ If the harness appears to be OK, observe the EGR position sensor display on the scan tool while moving connectors and wiring harnesses related to the EGR valve. A change in the display indicates the location of the malfunction.

In order to verify a repair, clear info with the scan tool and run the EGR flow test keeping the following conditions in mind:
^ The PCM will only run the EGR flow test during a gradual deceleration.
^ The PCM will only run the EGR test during a closed throttle condition.
^ The PCM will only run the EGR test at vehicle speeds above 62.5 km/h (37 mph).
^ Several deceleration cycle, usually 5-15 cycles, will be necessary in order to run a sufficient number of EGR flow test samples.
^ If within the enabling RPM the engine speed drops more than 500 RPM, the PCM will reset the test. Refer to Conditions For Running The DTC.
^ If within the enabling RPM the engine speed increases more than 75 RPM, the PCM will reset the test. Refer to Conditions For Running the DTC.
^ When the PCM commands the EGR valve open, the engine speed will drop. If the engine speed drops below 500 RPM, the test will not run.

If the condition is intermittent, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-8:

The number below refers to the step number on the diagnostic table.
2. This DTC is set when the PCM does not detect a predetermined change in MAP when the EGR valve is commanded. This step checks for any MAP sensor DTCs. A malfunctioning MAP sensor may cause this DTC to set.