GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 2001 🢒 Aurora 🢒 Engine 🢒 Engine Controls - 4.0L 🢒 DTC 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 the MAP. If the expected increase in the MAP is not seen, the PCM notes the amount of error that was detected and adjusts an internal failure counter toward a failure threshold level. When the failure counter exceeds the failure 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 1 EGR flow test sample to be taken during an ignition cycle. In order to help verify a repair, the PCM allows 15 test samples during the first ignition cycle following either a scan tool Clear Info or a battery disconnect. Five to 15 samples should be sufficient for the PCM to determine an adequate EGR flow and to 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 TP angle is less than 1.19 percent, deceleration.
    • The Deceleration Fuel Cut- Off (DFCO) steady for 0.3 seconds.
    • The ECT is between 80-110°C (176-230°F).
    • The engine speed is between 700-1200 RPM.
    • The IAC position is consistently more than 8 counts.
    • The MAP is steady between 15-70 kPa (2-10 psi).
    •  The vehicle speed is more than 60 k/h (37 mph) during deceleration.
    • The BARO sensor is more than 70 kPa (10 psi).
    • The vehicle will need to be driven above 81 k/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. During the test, 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 the EGR flow test indicate 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.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

IMPORTANT: Inspect for the following conditions:

   • An EGR valve that shows signs of excessive heat--Check the exhaust system for a blockage or for a plugged catalytic converter. Refer to the 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 OK, observe the EGR Position Sensor display on the scan tool while moving the connectors and the wiring harnesses that are related to the EGR valve. A change in the display indicates the location of the malfunction.

In order to verify a repair, select Clear Info on 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 60 k/h (37 mph).
    •  Several deceleration cycles will be necessary in order to run a sufficient number of EGR flow test samples A sufficient number of samples is usually 5-15 samples.
    • If within the enabling RPM the engine speed drops more than 500 RPM, the PCM will reset the test. Refer to the Conditions for Running the DTC in the text.
    • 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 in the text.
    • 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 .

Test Description

The number below refers to the step number on the diagnostic table.

  1. This DTC is set when the PCM does not detect a predetermined change in the 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.

DTC P0401

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Is there any MAP DTCs set?

Go to the applicable DTC

Go to Step 3

3
  1. Inspect the exhaust system for modification of original installed parts or for leaks.
  2. If you locate a problem, repair the exhaust system as necessary.

Did you find and correct the condition?

Go to Step 7

Go to Step 4

4
  1. Check the EGR valve gasket and pipes for leaks.
  2. If you locate a problem, clean or replace the EGR system components as necessary. Refer to Exhaust Gas Recirculation Pipe Replacement .

Did you find and correct the condition?

Go to Step 7

Go to Step 5

5
  1. Remove the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement .
  2. Inspect the following components for leaks and for restrictions:
    3. • The EGR pintle
    • The EGR valve passages

Did you find and correct the condition?

Go to Step 7

Go to Step 6

6
  1. Remove the EGR inlet and outlet pipes from the exhaust manifold and from the intake manifold. Refer to Exhaust Gas Recirculation Pipe Replacement .
  2. Inspect the manifold EGR ports and inspect the EGR inlet and outlet pipes for a blockage caused by excessive deposits or by other damage.

Did you find and correct the condition?

Go to Step 7

Go to Diagnostic Aids

7
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC, as specified in the supporting text.

Does the DTC run and pass ?

Go to Step 8

Go to Step 2

8

With a scan tool, observe the stored information, Capture info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK