GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Tracker - 4WD 🢒 Engine 🢒 Engine Controls - 2.5L (LE8) 🢒 Exhaust Gas Recirculation (EGR) System Diagnosis
Table 1: EGR Valve Terminal (Pin) Location

Circuit Description

The exhaust gas recirculation (EGR) system controls the formation of oxides of nitrogen (NOx) emissions by recirculating the exhaust gases into the combustion chamber. The EGR valve is a stepper motor design. The stepper motor moves a spring loaded plunger that controls the flow of exhaust gases into the intake manifold. The plunger movement is controlled by the powertrain control module (PCM). By turning the stepper motor in different directions, the PCM controls the opening of the exhaust gas passage to the intake manifold. The stepper motor has four coil windings that control the motor movement.

Diagnostic Aids

A normal engine operating temperature is specified as 80°C (176°F) or more.

An intermittent malfunction may be caused by a fault in the EGR control system electrical circuits. Inspect the EGR wiring 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) Location

Lock Tab

3

2

1

6

5

4

Test Description

The numbers below refer to the step numbers 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. A normal engine operating temperature is specified as 80°C (176°F) or more.

    3.

  3. This step checks the operation of the EGR valve. The EGR duty cycle output control is disabled by the powertrain control module (PCM) when any DTCs are stored and when 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 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.

    7.

  7. 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.

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

Use a scan tool and check for EGR system DTCs.

Is a DTC P0400 set?

--

Go to DTC P0400

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 10

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?

--

System OK

Go to Step 5

5
  1. Start the engine.
  2. Backprobe the following EGR coil control circuits at the PCM with a test lamp connected to ground.
    3. • C4-4
    • 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 6

Go to Step 7

6
  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 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 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 EGR valve assembly, and between pin 5 and the EGR assembly. The resistance should be infinite.

Does the EGR valve pass all the resistance tests?

20-24 ohms at 20°C (68°F)

Go to Step 9

Go to Step 15

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 18

Go to Step 15

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 harness side of terminal 5 and ground.

Does the test lamp illuminate on both circuits?

--

Go to Step 14

Go to Step 13

10

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

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

--

Go to Step 12

Go to Step 11

11
  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 18

--

12

  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 16

13

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

--

14
  1. Inspect for an open or a short in the EGR coil control circuits that did not illuminate On and Off in Step 5 or Step 6.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 18

Go to Step 16

15

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

Is the action complete?

--

Go to Step 18

--

16
  1. Inspect for poor electrical connections at the EGR valve and the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 18

Go to Step 17

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

Operate the vehicle within the conditions in which the customer concern was first noticed.

Is the customer concern still present?

--

Go to Diagnostic Trouble Code (DTC) List

System OK