GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2004 🢒 LeSabre 🢒 DTC 🢒 DTC P0405

Circuit Description

The exhaust gas recirculation (EGR) valve position sensor is monitored by the powertrain control module (PCM). The 5-volt reference circuit, low reference circuit and the EGR valve position signal circuit are used by the PCM to determine the EGR valve position. If the EGR valve position sensor signal voltage is pulled below a calibrated value, DTC P0405 sets.

Conditions for Running the DTC
    • The Ignition 1 Signal parameter is more than 11 volts.
    • The ignition is ON.
    • The EGR command will be disabled if the startup ECT is less than 5°C (41°F), and will not enable until the ECT is more than 75°C (167°F).

Conditions for Setting the DTC
    • The EGR Position Sensor parameter is less than 0.14 volts.
    • The above condition is met for more than 20 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 number below refers to the step number on the diagnostic table.

  1. By disconnecting each component one at a time, the component that is pulling the 5-volt reference circuit low will be revealed.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

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

Is DTC P0641 also set?

--

Go to DTC P0641

Go to Step 3

3

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

Is the EGR Position Sensor voltage parameter less than the specified value?

0.14 V

Go to Step 5

Go to Step 4

4
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. 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 5

Go to Intermittent Conditions

5
  1. Turn OFF the ignition.
  2. Disconnect the exhaust gas recirculation (EGR) valve.
  3. Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the exhaust gas recirculation (EGR) valve and the EGR valve position signal circuit.
  4. Turn ON the ignition, with the engine OFF.
  5. Observe the EGR Position Sensor parameter with a scan tool.

Is the EGR Position Sensor parameter more then the specified value?

4.9 V

Go to Step 11

Go to Step 6

6
  1. Disconnect the 3-amp fused jumper wire.
  2. Connect a test lamp between the 5-volt reference circuit of the EGR valve and the low reference circuit of the EGR valve

Does the test lamp illuminate?

--

Go to Step 10

Go to Step 7

7

Test the 5-volt reference circuit of the EGR valve for an open or for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 8

8

Test all 5-volt reference circuits 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 16

Go to Step 9

9

  1. Connect a DMM between the 5-volt reference circuit of the EGR valve and the low reference circuit of the EGR valve. Observe the voltage while disconnecting all sensors, one at a time, that use a 5-volt reference circuit. A change in voltage indicates the faulty component.
  2. Replace that component as necessary. Refer to the appropriate replacement procedure.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 12

10

Test the EGR valve position signal circuit for the following conditions:

    • A short to ground
    • An open
    • High resistance

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 12

11

Test the EGR valve position signal circuit for a short to the EGR solenoid high control circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 13

12

Test for an intermittent and for a poor connection at the powertrain control module (PCM). 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 16

Go to Step 15

13

Test for an intermittent and for a poor connection 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 16

Go to Step 14

14

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

Did you complete the replacement?

--

Go to Step 16

--

15

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 16

--

16
  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 17

17

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