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For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2000 🢒 Grand Prix 🢒 DTC 🢒 DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient

Circuit Description

The powertrain control module PCM tests the exhaust gas recirculation (EGR) system during deceleration by momentarily commanding the EGR valve open while monitoring the manifold absolute pressure (MAP) sensor signal. When the EGR valve is opened, the PCM should detect a proportional increase in the MAP. If the expected increase in MAP is not detected, the PCM notes the amount of error that was detected, and adjusts an internal failure counter toward a fail threshold level. When the failure counter exceeds the fail threshold level, DTC P0401 will set . The number of test samples required to accomplish this can vary according to the amount of detected flow error.

The PCM will only allow one EGR flow test sample to be taken during an ignition cycle. To help verify a repair, the PCM allows 12 test samples during the first ignition cycle following a scan tool Clear Info command, or following a battery disconnect. Nine to 12 samples should be sufficient for the PCM to determine adequate EGR flow, and to pass the EGR test if the system is operating correctly.

Conditions for Running the DTC
    • The following DTCs are not set:
       - Vehicle speed sensor (VSS)
       - Throttle position (TP) sensor
       - Engine misfire
       - Intake air temperature (IAT) sensor
       - Manifold absolute pressure (MAP) sensor
       - Idle speed
       - Fuel injector faults
       - Exhaust gas recirculation (EGR) pintle position
       - Manifold absolute pressure (MAP) sensor
       - Engine coolant temperature (ECT) sensor
       - Crankshaft position (CKP) sensor
       - Mass air flow (MAF) sensor
    • The BARO is more than 70 kPa.
    • The engine coolant temperature is more than 75°C (167°F).
    • The intake air temperature is more than 80°C (176°F).
    • The engine speed is between 900 RPM and 1400 RPM.
    • The IAC position is steady.
    • The vehicle speed is more than 25 MPH.
    • The throttle is closed.
    • The commanded state of the A/C relay is steady.

Conditions for Setting the DTC

That MAP changes that are monitored during the EGR flow test indicate insufficient EGR flow.

Action Taken When the DTC Sets
    • The PCM will illuminate the malfunction indicator lamp (MIL) during the first trip in which the diagnostic test has been run and failed.
    • The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

Conditions for Clearing the MIL/DTC
    • The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed.
    • The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
    • The DTC can be cleared by using a scan tool.

Diagnostic Aids

Important: If the EGR valve shows signs of excessive heat, inspect the exhaust system for blockage. A plugged catalytic converter can cause blockage. Refer to Restricted Exhaust System Check .

in order to verify a repair, clear the scan tool and run the EGR flow test keeping the following items 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 during vehicle speeds above 25 MPH.
    • Several deceleration cycles will be necessary in order to run a sufficient number of EGR flow test samples, typically 9 to 12 samples.
    • If the engine speed increases more than 100 RPM for VIN K, or if the engine speed increases more than 200 RPM for VIN 1 from the enabling RPM, the PCM will reset the test.
    • If the engine speed decreases more than 300 RPM for VIN K, or if the engine speed decreases more than 350 RPM for VIN 1 from the enabling RPM, the PCM will reset the test.
    • When the PCM commands the EGR valve open, the engine speed will drop. If the engine speed drops to less than 700 RPM, the test will not run.
    • The EGR Test Counter displayed on the scan tool can help to determine that the EGR flow test is running and can keep track of the number of test samples taken. The counter will increment each time a test sample is taken.

Inspect for the following conditions:

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. Inspect for objects that block the vacuum to the MAP sensor. Also inspect for kinked or pinched MAP sensor vacuum hoses, if the vehicle is so equipped.

Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

Important: :  Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

    • Loose terminal connection
       -  Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.
       -  Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.
    • Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.
    •  Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.

DTC P0401 - EGR Flow Insufficient Detected

Step

Action

Values

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2
  1. Inspect the exhaust system for modification of original installed parts or for leaks.
  2. Repair the condition as necessary.

Did you find and correct the condition?

--

Go to Step 5

Go to Step 3

3
  1. Remove the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement .
  2. Inspect the following items:
    3. • The pintle, the valve passages, and the adapter for excessive deposits or for any kind of a restriction.
    • The EGR valve gasket and the pipes for leaks.
  3. Repair the condition as necessary.

Did you find and correct the condition?

--

Go to Step 5

Go to Step 4

4
  1. Remove the EGR inlet and outlet pipes from the exhaust manifold and from the intake manifold. Refer to Evaporative Emission System Hoses/Pipes Replacement .
  2. Inspect the manifold EGR ports and the EGR inlet and outlet pipes for a blockage caused by excessive deposits, or for other damage.
  3. Repair the condition as necessary.

Did you find and correct the condition?

--

Go to Step 5

Go to Diagnostic Aids

5
  1. Use a scan tool in order to clear the DTCs.
  2. Monitor the EGR Test Count with a scan tool while operating the vehicle within the Conditions for Running, as specified in the supporting text.
  3. Continue operating the vehicle you have 9 to 12 test samples.

Does the DTC reset?

--

Go to Step 2

System OK