GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Venture - 4WD 🢒 Restraints 🢒 SIR 🢒 DTC P0401

Circuit Description

The powertrain control module (PCM) tests the exhaust gas recirculation (EGR) system during deceleration. The PCM does this by momentarily commanding the EGR valve to open while monitoring the signal circuit of the manifold absolute pressure (MAP) sensor. When the EGR valve is opened, the PCM will expect to see a predetermined increase in MAP. If the expected increase in MAP is not detected, the PCM records the amount of MAP difference that was detected and adjusts a calibrated fail counter towards a calibrated fail threshold level. The number of EGR flow test counts required to exceed the fail threshold may vary according to the amount of detected EGR flow error.

Normally, the PCM will only allow one EGR flow test during an ignition cycle. To aid in verifying a repair, the PCM will allow up to 12 EGR flow test counts during the first ignition cycle following a code clear event. Between 9-12 EGR flow test counts should be sufficient for the PCM to determine adequate EGR flow and pass the EGR flow test. If the PCM detects an EGR flow error, DTC P0401 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient

Conditions for Running the DTC
    • DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0403, P0404, P0405, P0406, P0502, P0503, P0506, P0507, P0641, P0651, P1404 are not set.
    • The engine run time may need to be more than 3 seconds.
    • The Ignition 1 signal parameter is between 11-18 volts.
    • The EGR position is less than one percent.
    • The AC Relay Command parameter does not change for more than one second.
    • The Current Gear parameter does not change for more than 1.5 seconds.
    • The transmission is in 3rd or 4th gear.
    • The Intake Air Temperature (IAT) sensor parameter is between -10 to +100°C (14-212°F).
    • The Engine Coolant Temperature (ECT) sensor parameter is more than 75°C (167°F).
    • The Engine Speed parameter is between 1,000-1,400 RPM.
    • The Manifold Absolute Pressure (MAP) sensor parameter is between 15-70 kPa.
    • The MAP sensor parameter does not change more than 3 kPa.
    • The Barometric Pressure (BARO) parameter is more than 70 kPa.
    • The power enrichment (PE) mode is not active.
    • The decel fuel cut off (DFCO) mode is not active.
    • The Throttle Position (TP) sensor parameter is less than one percent for more than 0.5 second.
    •  The Vehicle Speed sensor parameter is between 43-109 km/h (30-65 mph) during deceleration.
    • The Vehicle Speed Sensor parameter does not change more than 8 kmh (5 mph).
    • The Idle Air Control (IAC) Position parameter does not change more than 5 counts while the above conditions are met.
    • The above conditions must be met for 0.5 second.
    • The vehicle will need to be driven more than 80 km/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 EGR flow test to run. The EGR Flow Test Count parameter on the scan tool will increment when each EGR flow test is completed.
    • DTC P0401 may run a maximum of 9 tests after a code clear with a minimum of 0.5 second between each test.

Conditions for Setting the DTC

The MAP changes monitored by the PCM during the EGR flow tests indicate an insufficient amount of 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

Inspect for the following conditions:

    • A vacuum restriction to the MAP sensor--A skewed MAP sensor reading can cause the PCM to read incorrect MAP changes during the EGR flow test.
    • An engine that is running poorly due to a mechanical condition such as worn piston rings, worn camshaft, etc.--These types of conditions can cause low engine vacuum and thus can cause a less than expected MAP changes during the flow test.
    • Excessive back pressure in the exhaust system may cause this DTC to set. This condition can cause low engine vacuum and thus can cause a less than expected MAP changes during the EGR flow test. Possible causes of this could be a restriction in the exhaust system or non original equipment manufacture (OEM) exhaust parts.
    • Exhaust system leaks can cause an insufficient amount of EGR flow through the EGR valve. This condition can cause a less than expected MAP changes due to insufficient exhaust back pressure. possible causes of this could be a leaking exhaust system, a leaking EGR pipe or non original equipment manufacture (OEM) exhaust parts.
    • A restriction in the intake manifold such as carbon deposits and casting flash

Test Description

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

  1. MAP sensor faults must be diagnosed first. A skewed MAP sensor reading could cause this DTC to set.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Is DTC P0107 or P0108 also set?

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

Go to Step 3

3

Inspect the exhaust system for leaks, restrictions, and for modification of original equipment manufacture (OEM) parts.

Did you find and correct the condition?

Go to Step 7

Go to Step 4

4

Inspect for a vacuum leak between the exhaust gas recirculation (EGR) valve and the intake manifold.

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 EGR valve pintle and the EGR valve passages for leaks or for restrictions. Refer to Exhaust Gas Recirculation (EGR) System Cleaning or Exhaust Gas Recirculation Valve Replacement .

Did you find and correct the condition?

Go to Step 7

Go to Step 6

6
  1. Remove the EGR valve inlet pipe from the exhaust manifold. Refer to Exhaust Gas Recirculation Pipe Replacement .
  2. Inspect the exhaust manifold EGR port and the EGR valve pipe for a restriction.

Did you find and correct the condition?

Go to Step 7

Go to Diagnostic Aids

7
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
  5. Observe the EGR Flow Test Count parameter on the scan tool. 9-12 EGR Flow Test counts may be necessary to pass this DTC after the DTCs have been cleared.

Did the DTC fail this ignition?

Go to Step 2

Go to Step 8

8

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK