GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 1999 🢒 Intrigue 🢒 Engine 🢒 Engine Controls - 3.5L 🢒 DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient

Circuit Description

The PCM tests the 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 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 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 15 test samples during the first ignition cycle following a scan tool Clear Info or a battery disconnect. Between six and nine samples should be sufficient for the PCM to determine adequate EGR flow and pass the EGR test if the system is operating correctly.

Conditions for Running the DTC
  1. No Fuel injector faults, Misfire, Idle speed, EGR Pintle Position, VSS, TP, IAT, MAP, ECT, CKP or MAF sensor DTCs set.
  2. BARO is greater than 77 kPa.
  3. Engine coolant temperature is greater than 80°C (176°F).
  4. Engine speed is between 900 RPM and 1300 RPM.
  5. Vehicle speed is greater than 22.5 MPH.
  6. The throttle is closed.
  7. EGR pintle position less than 1% (valve closed).
  8. IAC position, MAP, engine rpm and vehicle speed steady.
  9. A/C clutch state and transmission state unchanged.

Conditions for Setting the DTC

MAP changes monitored during the EGR flow test indicate insufficient EGR flow.

Action Taken When the DTC Sets
    • The PCM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
    • The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame and/or Failure Records.

Conditions for Clearing the MIL/DTC
    • The PCM turns the MIL Off after three consecutive drive trips that the diagnostic runs and does not fail.
    • A last test failed (current DTC) clears when the diagnostic runs and does not fail.
    • A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
    • Use a scan tool in order to clear the MIL/DTC.
    • Interrupting the PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Powertrain Control Module (PCM) Description , Clearing Diagnostic Trouble Codes.

Diagnostic Aids

Notice: Use the connector test adapter kit J 35616-A for any test that requires probing the following items:

   • The PCM harness connectors
   • The electrical center fuse/relay cavities
   • The component terminals
   • The component harness connector
Using this kit will prevent damage caused by the improper probing of connector terminals.

Important: If the EGR valve shows signs of excessive heat, check the exhaust system for blockage (possibly a plugged catalytic converter). Refer to the Restricted Exhaust System Check .

To verify a repair, clear info with 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 at vehicle speeds above 22.5 MPH.
    • Several deceleration cycles will be necessary to run a sufficient number of EGR flow test samples (6-9).
    • The EGR Flow Test Counter displayed on the scan tool can be useful in determining that the EGR flow test is running and to keep track of the number of test samples taken. The counter will increment each time a test sample is taken.

Check for 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. Check for objects blocking the vacuum to the MAP sensor.

Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

If the problem is intermittent, refer to Intermittent Conditions .

Step

Action

Value(s)

Yes

No

1

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

--

Go to Step 2

Go to the Powertrain On Board Diagnostic (OBD) System Check

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

Was a problem found and corrected?

--

Go to Step 5

Go to Step 3

3
  1. Remove the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement .
  2. Visually and physically inspect the following items:
    3. • The pintle, the valve passages and the adapter for excessive deposits or any kind of a restriction.
    • The EGR valve gasket and pipes for leaks.
  3. If a problem is found, clean or replace EGR system components as necessary. Refer to Exhaust Gas Recirculation (EGR) System Cleaning

Was a problem found and corrected?

--

Go to Step 5

Go to Step 4

4
  1. Remove the EGR inlet and outlet pipes from the exhaust manifold and the intake manifold. Refer to Exhaust Gas Recirculation Pipe Replacement .
  2. Inspect the crossover assembly and the EGR inlet and outlet pipes for a blockage caused by excessive deposits or other damage. Refer to Exhaust Gas Recirculation (EGR) System Cleaning
  3. If a problem is found, correct the condition as necessary.

Was a problem found and corrected?

--

Go to Step 5

Refer to Diagnostic Aids.

5
  1. Review and record the scan tool Failure Records data.
  2. Clear DTC and monitor EGR Test Count display on the scan tool while operating the vehicle as specified in DTC P0401 Diagnostic Aids.
  3. Continue operating the vehicle until 9 -12 test samples have been taken.
  4. Select scan tool Specific DTC information for DTC P0401.

Note test result; does scan tool indicate DTC P0401 Test Ran and Passed?

--

Go to Step 6

Go to Step 2

6

Review Captured Info using the scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to the applicable DTC table

System OK