GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The exhaust gas recirculation (EGR) vacuum sensor is used to monitor the amount of vacuum that is available to the EGR valve. A low reference circuit, 5 volt reference circuit and a vacuum sensor signal circuit are used to interface the ECM with the EGR vacuum sensor. If the EGR vacuum sensor signal voltage is above a calibrated value, DTC P0406 sets.

Conditions for Running the DTC

    • DTC P1639 is not set.
    • The ignition is ON.
    • The Ignition 1 Signal parameter is between 11-18 volts.

Conditions for Setting the DTC

    • The EGR Vacuum Sensor parameter is more than 158 kPa.
    • The above conditions are met for more than 5 seconds.

Action Taken When the DTC Sets

    • The control module illuminates the malfunction indicator lamp (MIL) on the second 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 3 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.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. If DTC P1639 sets, there is a short to voltage on the 5-volt reference circuit. Perform the DTC P1639 diagnostic before proceeding.

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

Is DTC P1639 also set?

--

Go to DTC P1639

Go to Step 3

3

  1. Start the engine.
  2. Command the EGR Solenoid to 100 % with a scan tool.
  3. Observe the EGR Vacuum Sensor parameter with a scan tool.

Is the EGR Vacuum Sensor parameter more than the specified value?

158 kPa

Go to Step 4

Go to Intermittent Conditions

4

  1. Turn OFF the ignition.
  2. Disconnect the EGR vacuum sensor harness connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the low reference circuit of the EGR vacuum sensor and B+.

Does the test lamp illuminate?

--

Go to Step 6

Go to Step 5

5

Test the low reference circuit of the EGR vacuum sensor for high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 7

6

  1. Disconnect the EGR vacuum sensor harness connector.
  2. With a scan tool, observe the EGR vacuum sensor parameter.

Does the scan tool indicate that the EGR Vacuum Sensor parameter is less than the specified value?

18 kPa

Go to Step 8

Go to Step 7

7

Test the signal circuit of the EGR vacuum sensor for a short to voltage. Refer to Testing for a Short to Voltage and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

8

Test for an intermittent and for a poor connection at the EGR vacuum sensor. 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 12

Go to Step 10

9

Test for an intermittent and for a poor connection at the 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 12

Go to Step 11

10

Replace the EGR vacuum sensor. Refer to Exhaust Gas Recirculation Valve Vacuum Sensor Replacement .

Did you complete the replacement?

--

Go to Step 12

--

11

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 12

--

12

  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 13

13

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