2001 Chevrolet/Geo Camaro  

DTC P0401

Circuit Description

The powertrain control module (PCM) tests the exhaust gas recirculation (EGR) system during deceleration by momentarily commanding the EGR valve to 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 this diagnostic trouble code (DTC). 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 1 EGR flow test sample to be taken during an ignition cycle. To aid in verifying a repair, the PCM allows 12 test samples during the first ignition cycle following a scan tool Clear Info or a battery disconnect. Between 9-12 samples should be sufficient for the PCM to determine adequate EGR flow and pass the EGR test.

Conditions for Running the DTC
Conditions for Setting the DTC

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

Action Taken When the DTC Sets
Conditions for Clearing the MIL/DTC
Diagnostic Aids

Important

Inspect for the following conditions:

In order to verify a repair, clear info with the scan tool and run the EGR flow test, keeping the following items in mind:

Test Description

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

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

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Is there any MAP DTCs set?

Go to the applicable DTC

Go to Step 3

3
  1. Inspect the exhaust system for modification of original installed parts or for leaks.
  2. Repair the exhaust system as necessary.

Did you find and correct the condition?

Go to Step 7

Go to Step 4

4
  1. Check the EGR valve gasket and pipes for leaks.
  2. Clean or replace the EGR system components as necessary.

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 (EGR) Valve Replacement .
  2. Inspect the following items for a leak or for a restriction:
    • The EGR pintle
    • The EGR valve passages

Did you find and correct the condition?

Go to Step 7

Go to Step 6

6
  1. Remove the EGR inlet and outlet pipes from the exhaust manifold and the intake manifold--Refer to Exhaust Gas Recirculation (EGR) Inlet Pipe Replacement and Exhaust Gas Recirculation (EGR) Outlet Pipe Replacement .
  2. Inspect the manifold EGR ports and the EGR inlet and outlet pipes for a blockage caused by excessive deposits or other damage.

Did you find and correct the condition?

Go to Step 7

Go to Diagnostic Aids

7
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run, and pass ?

Go to Step 8

Go to Step 2

8

Use a scan tool, in order to observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK