GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2004 🢒 Tracker - 4WD 🢒 Engine 🢒 Engine Controls - 2.0L 🢒 DTC P0401
Table 1: EGR Valve Terminal (Pin) Identification

Circuit Description

The DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient diagnostic monitors the operation of the EGR valve. The EGR system controls the formation of oxides of nitrogen (NOx) emissions by recirculating the exhaust gases into the combustion chamber. The powertrain control module (PCM) uses the expected changes in the manifold absolute pressure (MAP) sensor readings in order to evaluate the performance of the EGR system. The PCM sends a signal to the EGR valve while monitoring the MAP sensor signal. The PCM sets DTC P0401 when the monitored MAP sensor pressure change is less than the expected value.

Conditions for Running the DTC
    • Barometric pressure (BARO) is more than or equal to 75 kPa.
    • Engine coolant temperature is between 70°C and +110°C (158°F-230°F).
    • Intake air temperature is more than -8°C (+18°F).
    • Vehicle speed is at least 97 km/h (60 mph) for 7 minutes prior to deceleration.
    • The vehicle is allowed to decelerate with no accelerator or brake pedal input.
    • During deceleration the throttle valve angle is 0 degrees, and the engine is operating in Fuel Cutoff mode.

Conditions for Setting the DTC

The difference in intake manifold pressure between when the EGR valve is OPEN, and when the EGR valve is CLOSED, is less than a specified value.

Action Taken When the DTC Sets
    • The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault.
    • The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

Conditions for Clearing the MIL/DTC
    • The PCM turns OFF the MIL after 3 consecutive trips without a fault.
    • The PCM clears a history DTC after 40 consecutive warm-up cycles without a fault.
    • You perform the scan tool Clear DTC Information function.

Diagnostic Aids

A DTC P0401 is more likely to set during short trips on the highway. Operate the vehicle on the highway, with frequent closed throttle stops, in order to validate a DTC P0401.

Check for any of the following conditions:

    • An EGR valve that is stuck closed, stuck open, or binding.
    • The incorrect PCM can cause DTC P0401 to set. Check that the correct PCM is installed in the vehicle as required for proper emission certification.

A DTC P0401 sets when the change in MAP signal is less than the expected value during the operation of the EGR valve. Investigate any condition that can affect the accuracy of the MAP sensor readings:

    • Retarded ignition timing
    • Restricted exhaust system
    • Faulty MAP sensor
    • Restriction or a leak that affects the flow of exhaust gases through the EGR valve and into the intake air system.

If a DTC P0401 is intermittent, driving the vehicle under the conditions outlined in the Inspection/Maintenance (I/M) section can verify whether the fault is present. Refer to Inspection/Maintenance (I/M) Exhaust Gas Recirculation (EGR) System Set Procedure .

An intermittent malfunction may be caused by a fault in the EGR valve or MAP sensor electrical circuits. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .

If a DTC P0401 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC was first set.

Use the following table in order to locate the correct terminals to test during diagnosis. The table layout corresponds to the pin location of the EGR valve electrical terminals.

EGR Valve Terminal (Pin) Identification

Connector Lock Tab

Pin 3

Pin 2

Pin 1

Pin 6

Pin 5

Pin 4

Test Description

The number below refer to the step number in the diagnostic table.

  1. The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

    2.

  2. This step checks for an EGR valve that is leaking, stuck open, or turned on at idle. Normal engine operating temperature is specified as 80°C (176°F) or above.

    3.

  3. This step checks the operation of the EGR valve. The duty cycle output control of the EGR is disabled by the PCM when any DTCs are stored and when the engine temperature is less than 80°C (176°F).

    4.

  4. This step checks for a physically stuck EGR valve or plugged EGR passages.

    5.

  5. This step checks the ignition positive voltage supply to the EGR coils.

    6.

  6. This step checks for proper manifold absolute pressure (MAP) sensor operation. The diagnostic for a DTC P0401 depends on MAP sensor output in order to monitor EGR valve performance.

    7.

  7. Fault not present indicates the condition that caused DTC P0401 to set is intermittent and not currently present. If no other DTCs are stored, refer to Diagnostic Aids for additional information on diagnosing an intermittent DTC P0401.

    8.

  8. This step determines whether an electrical fault is the cause of the EGR valve staying open. A grounded EGR valve control circuit can cause the EGR valve to be open all the time.

    9.

  9. This step checks for an EGR valve control circuit that is shorted to ground. If the circuit wiring is OK, a faulty PCM with an internally shorted circuit can cause the EGR valve to be open.

    10.

  10. Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. The DTC P0401 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0401 appears in the Not Ran Since Code Cleared list, the DTC P0401 diagnostic has not yet run. When the DTC P0401 does not appear in the Not Ran Since Code Cleared list, the DTC P0401 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the DTC P0401 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status, in order to determine the outcome of the diagnostic test involved.

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Is DTC P0403 also set?

--

Go to DTC P0403

Go to Step 3

3

  1. Start the engine.
  2. Run the engine at a normal operating temperature.

Does the engine run rough, or is the idle unstable?

--

Go to Step 12

Go to Step 4

4

  1. Install a scan tool.
  2. Perform the scan tool Clear DTC Information function.
  3. Start the engine.
  4. Using the scan tool, gradually command the EGR valve OPEN to 100 percent.

Does the engine run rough or stall?

--

Go to Step 10

Go to Step 5

5
  1. Start the engine.
  2. Backprobe the EGR control circuits pin 1 and pin 4 with a test lamp connected to ground. Refer to the EGR Valve Terminal Identification table in Diagnostic Aids.
  3. The test lamp should illuminate on both circuits.
  4. Continue to backprobe both EGR control circuits with the test lamp.
  5. Observe the test lamp on each circuit while commanding the EGR valve OPEN to the specified value with the scan tool.
  6. The test lamp should illuminate and then turn OFF when the EGR valve is commanded OPEN.

Does the EGR valve pass both tests?

5%

Go to Step 6

Go to Step 7

6
  1. Start the engine.
  2. Backprobe the EGR control circuits pin 3 and pin 6 with a test lamp connected to ground.
  3. The test lamp should NOT illuminate on either circuit.
  4. Continue to backprobe both EGR control circuits with the test lamp.
  5. Observe the test lamp on each circuit while commanding the EGR valve OPEN to the specified value with the scan tool.
  6. The test lamp should illuminate when the EGR valve is commanded OPEN.

Does the EGR valve pass both tests?

5%

Go to Step 8

Go to Step 7

7
  1. Turn OFF the ignition.
  2. Disconnect the EGR valve electrical connector.
  3. Use a digital multimeter (DMM) to measure the following EGR valve coil windings for the specified value of resistance. Refer to the EGR Valve Terminal Identification table in Diagnostic Aids.
    4. • Between pin 1 and pin 2
    • Between pin 2 and pin 3
    • Between pin 5 and pin 6
    • Between pin 4 and pin 5
  4. Measure the resistance between pin 2 and the EGR valve assembly, and between pin 5 and the EGR assembly. The resistance should be infinite.

Does the EGR valve pass all resistance tests?

20-24 ohms at 20°C (68°F)

Go to Step 9

Go to Step 17

8

  1. Remove the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement .
  2. Inspect the EGR system for the following conditions:
    3. • Inspect all the EGR passages for any obstruction or blockage.
    • Inspect the EGR valve for physical damage or carbon deposits.
  3. Repair as necessary.

Was a repair necessary?

--

Go to Step 19

Go to Step 17

9

  1. Disconnect the EGR valve electrical connector.
  2. Turn ON the ignition, leaving the engine OFF.
  3. Connect a test lamp between the harness side of terminal 2 and ground.
  4. Connect a test lamp between the harness side of terminal 5 and ground.

Did the test lamp illuminate for both circuits?

--

Go to Step 16

Go to Step 15

10

  1. Inspect the vehicle for any condition that can affect the accuracy of the manifold absolute pressure (MAP) sensor:
    2. • A malfunctioning or incorrectly calibrated MAP sensor
    • A faulty manifold vacuum supply to the MAP sensor
    • An engine performance concern that can affect the engine manifold vacuum readings
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 19

Go to Step 11

11

The fault is not present.

Are there any DTCs stored that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Diagnostic Aids

12

With the engine running, disconnect the EGR valve electrical connector.

Does the engine performance improve when the EGR valve is disconnected?

--

Go to Step 14

Go to Step 13

13
  1. Remove the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement .
  2. Inspect the EGR valve for any of the following conditions:
    3. • Inspect the EGR valve for sticking open
    • Inspect the EGR valve and the gasket for leaks
  3. Repair or replace as necessary.

Is the action complete?

--

Go to Step 19

--

14

  1. Inspect the EGR coil control circuits for a short to ground.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 19

Go to Step 18

15

Repair the ignition positive voltage supply to the EGR valve. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 19

--

16
  1. Inspect for an open or a short in the EGR coil control circuits between the EGR valve and the PCM.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 19

Go to Step 18

17

Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement .

Is the action complete?

--

Go to Step 19

--

18

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 19

--

19

  1. Turn OFF the ignition.
  2. Remove the DOME fuse for 30 seconds.
  3. Install the DOME fuse.
  4. Reset the radio clock time. Refer to Radio/Audio System Description and Operation in Entertainment.
  5. Start the engine.
  6. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or until the DTC P0401 diagnostic test has run.

Does the DTC run and pass?

--

Go to Step 20

Go to Step 2

20

With a scan tool, 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