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

Conditions for Setting the DTC

Action Taken When the DTC Sets

Conditions for Clearing the MIL/DTC

Diagnostic Aids

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:

Inspect for the following conditions:

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed helps determine when the condition that caused the DTC to be set occurred. This may assist in diagnosing the condition.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This DTC is set when the PCM does not detect a predetermined change in MAP when the EGR valve is commanded. This step inspects for any MAP or MAF sensor DTCs. A malfunctioning MAP or MAF sensor may cause this DTC to set.

DTC P0401 - EGR Flow Insufficient Detected







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


Go to Step 2

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


Is there any MAP or MAF DTC's set?


Go to the applicable DTC

Go to Step 3


  1. Inspect the exhaust system for modification of original installed parts or leaks. Refer to Exhaust Leakage in Engine Exhaust.
  2. Repair the exhaust system as necessary if you locate a condition.

Did you find and correct the condition?


Go to Step 7

Go to Step 4


Inspect the EGR valve gasket and pipes for leaks. Clean or replace the EGR system components as necessary if you locate a condition. Did you find and correct the condition?


Go to Step 7

Go to Step 5


  1. Remove the EGR valve. Refer to EGR Valve Replacement .
  2. Visually and physically inspect the following items for a leak and/or a restriction:
    • The EGR pintle
    • The EGR valve passages

Did you find and correct the condition?


Go to Step 7

Go to Step 6


  1. Remove the EGR inlet and outlet pipes from the exhaust manifold and the intake manifold. Refer to EGR System Cleaning .
  2. Inspect the manifold EGR ports and the EGR inlet and outlet pipes for a blockage caused by excessive deposits or other damage.
  3. Correct the condition as necessary.

Did you find and correct the condition?


Go to Step 7

Go to Diagnostic Aids


  1. Select the Diagnostic Trouble Code (DTC) option and the Clear DTC option using the scan tool.
  2. Idle the engine at the normal operating temperature.
  3. Select the Diagnostic Trouble Code (DTC) option and the Specific DTC option, then enter the DTC number using the scan tool.
  4. Operate vehicle within the Conditions for Running this DTC as specified in the supporting text, if applicable.

Does the scan tool indicate that this test failed?


Go to Step 8

Go to Step 2


Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed?


Go to applicable DTC

System OK