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. The pressure in the intake manifold increases when the EGR valve is open. The PCM monitors the Manifold Absolute Pressure (MAP) sensor signal during the EGR system diagnostic in order to determine the amount of EGR flow. The PCM calculates an error based on the difference between the actual MAP increase and a predetermined value. The PCM records the error and adjusts an internal fail counter towards the fail threshold if the error is too great. The PCM sets a DTC P0401 when the fail counter exceeds the fail threshold. The number of test samples required to exceed the fail threshold varies according to the magnitude of the detected flow errors.

The PCM allows only one EGR flow test sample to be taken during an ignition cycle. Following a scan tool Clear Info or a battery disconnect the PCM allows twelve test samples during the first ignition cycle in order to aid in verifying a repair.

Conditions for Running the DTC

• DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0405, P0500, P0502, P0503, P0562, P0563, P1404 are not set.
• The ignition voltage is between 11.7 and 18 volts.
• The BARO is greater than 70 kPa.
• The ECT is between 60°C (140°F) and 117°C (243°F).
• The IAT is less than 65°C (140°F).
• The TP sensor angle is less than 1.1%
• The engine speed is between 800 RPM and 2,000 RPM.
• The engine vacuum (BARO minus MAP) is between 60 kPa (9 psi) and 83 kPa (12 psi).
• The IAC position is steady.
• The vehicle speed is between 42 km/h (26 mph) and 113 km/h (70 mph).
• The change in VSS is less 6 km/h (4 mph).
• The change in MAP is less than 0.5 kPa.
• The A/C clutch status is steady.
• Not in fuel deceleration cut-off.

Conditions for Setting the DTC

• The change in the MAP is less than a predetermined value during the EGR flow test.
• All conditions present for 2.0 seconds.

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 OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
• A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
• 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

1. Use a scan tool in order to clear info. Run the EGR flow test in order to verify a repair. Keep the following items in mind when running the EGR flow test:
• The PCM runs the EGR flow test during a gradual deceleration.
• The PCM runs the EGR flow test during a closed throttle condition.
• The PCM runs the EGR flow test at vehicle speeds between 42 km/h (26 MPH) and 113 km/h (70 MPH).
• Several deceleration cycles will be necessary to run a sufficient number of EGR flow test samples (9-12).
2. 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 blocking the vacuum to the MAP sensor.
• An engine that is running poorly may cause this DTC to set.
• Poor connections or a damaged harness.
• If the harness appears to be OK, observe the Actual EGR Position 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.
3. Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can aid in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also aid determining how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This isolates when the DTC failed.
4. For an intermittent, refer to Symptoms .

Test Description

The numbers below refer to the step numbers 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. A malfunctioning MAP sensor may cause this DTC to set.