GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Tracker - 4WD 🢒 Engine 🢒 Engine Controls - 2.5L (LE8) 🢒 DTC P0400
Table 1: EGR Valve Terminal (Pin) Identification

Circuit Description

The DTC P0400 Exhaust Gas Recirculation (EGR) System 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 suspects that the EGR valve flow is incorrect when the monitored MAP sensor pressure change is too small.

Conditions for Running the DTC
    • The barometric pressure (BARO) is more than or equal to 75 kPa.
    • The engine coolant temperature is between 70-110°C (158-230°F).
    • The intake air temperature is more than -8°C (+18°F).
    • The vehicle speed is between 48-64 km/h (30-40 mph).
    • The engine speed is between 2,000-3,000 RPM for 3 minutes.

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 active.
    • 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 MIL turns OFF after 3 consecutively passing trips without a fault present.
    • A history DTC clears after 40 consecutive warm-up cycles without a fault.
    • Perform the scan tool Clear DTC Information function in order to clear the DTC.

Diagnostic Aids

A DTC P0400 is more likely to set during a short trips on the highway. Operate the vehicle on the highway, with frequent closed throttle stops, in order to validate a DTC P0400.

Check for any of the following conditions:

    • An EGR valve that is stuck closed, stuck open, or binding.
    • The incorrect PCM can cause DTC P0400 to set. Check that the correct PCM is installed in the vehicle as required for proper emission certification.

A DTC P0400 may set when the expected change in MAP is more than or 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:

    • A retarded ignition timing
    • A restricted exhaust system
    • A faulty MAP sensor
    • A restriction or a leak that affects the flow of exhaust gases through the EGR valve and into the intake air system.

If a DTC P0400 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 .

If a DTC P0400 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.

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 .

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 P0400 depends on MAP sensor output in order to monitor EGR valve performance.

    7.

  7. Fault not present indicates the condition that caused DTC P0400 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 P0400.

    8.

  8. This step determines whether an electrical fault is the cause of the EGR valve staying open. An EGR valve control circuit that becomes shorted or open when the EGR valve is open, can cause the valve to remain 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. This step checks whether the malfunction that caused the DTC P0400 is still present. Driving the vehicle under these conditions will verify whether the fault is present. After performing the scan tool Clear DTC Information function, the DTC P0400 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If DTC P0400 appears in the Not Ran Since Code Cleared list, the DTC P0400 diagnostic has not yet run. When DTC P0400 does not appear in the Not Ran Since Code Cleared list, the DTC P0400 diagnostic has run. If the MIL is NOT illuminated and there is no Pending DTC Status in DTC Information, the DTC P0400 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

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

  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 11

Go to Step 3

3

  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 9

Go to Step 4

4
  1. Start the engine.
  2. Backprobe the following EGR coil control circuits at the PCM with a test lamp connected to ground.
    3. • C4-4
    • C4-17
  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 5

Go to Step 6

5
  1. Start the engine.
  2. Backprobe the following EGR coil control circuits at the PCM with a test lamp connected to ground.
    3. • C4-5
    • C4-16
  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 7

Go to Step 6

6
  1. Turn OFF the ignition.
  2. Disconnect the EGR valve electrical connector.
  3. Use a 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 8

Go to Step 16

7

  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 18

Go to Step 16

8

  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 15

Go to Step 14

9

  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 18

Go to Step 10

10

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

11

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

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

--

Go to Step 13

Go to Step 12

12
  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 the condition or replace the EGR valve.

Did you complete the repair or replacement?

--

Go to Step 18

--

13

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

Was a repair necessary?

--

Go to Step 18

Go to Step 17

14

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

Is the action complete?

--

Go to Step 18

--

15
  1. Inspect for an open or a short in the EGR coil control circuits that did not illuminate On and Off in Step 4 or Step 5.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 18

Go to Step 17

16

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

Is the action complete?

--

Go to Step 18

--

17

Important: The replacement PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 18

--

18

  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 19

Go to Step 2

19

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