GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The coil of the exhaust gas recirculation (EGR) valve has 12 volts supplied to it by an ignition voltage circuit. The control circuit of the EGR valve is a pulse width modulated (PWM) ground produced by an internal low side driver of the engine control module (ECM). The ECM monitors the position of the EGR pintle through the EGR position sensor. The EGR position sensor sends a feedback voltage on the signal circuit to the ECM. This voltage varies depending on the position of the EGR valve pintle. The ECM interprets this voltage as the position of the EGR valve pintle. If the ECM determines that EGR valve pintle is open during crank, DTC P0402 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0402 Exhaust Gas Recirculation (EGR) Flow Excessive

Conditions for Running the DTC

    • The engine is cranking.
    • The ignition voltage is between 10-16 volts.
    • DTC P0402 runs continuously once the above conditions are met .

Conditions for Setting the DTC

The ECM detects excessive EGR flow due to the EGR valve pintle being open more than 70 percent for 3 seconds during crank.

Action Taken When the DTC Sets

    • The control module illuminates the malfunction indicator lamp (MIL) on the third consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

    • The control module turns OFF the malfunction indicator lamp (MIL) after 4 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Turn ON the ignition, with the engine OFF.
  2. Observe the EGR Position Sensor parameter with a scan tool.

Is the percentage within the specified range?

0-3%

Go to Step 3

Go to Step 4

3

  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Intermittent Conditions

4

  1. Disconnect the harness connector of the exhaust gas recirculation (EGR) valve.
  2. Turn ON the ignition, with the engine OFF.
  3. Probe the control circuit of the EGR valve with a test lamp that is connected to battery voltage.

Does the test lamp illuminate?

--

Go to Step 6

Go to Step 5

5

  1. Turn OFF the ignition.
  2. Remove the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement .
  3. Inspect the EGR valve for carbon deposits or foreign material between the EGR pintle and seating surface.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 9

6

Test the control circuit of the EGR valve for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 7

7

Test for short terminals and poor connections at the EGR valve. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 8

8

Test for short terminals and poor connections at the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 10

9

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

Did you complete the replacement?

--

Go to Step 11

--

10

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 11

--

11

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 12

12

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK