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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Sierra - 2WD (LPG) 🢒 DTC 🢒 DTC P0405

Circuit Description

The powertrain control module (PCM) and the alternative fuels ECM monitor the exhaust gas recirculation (EGR) valve pintle position. If the alternative fuels ECM detects an excessively low EGR valve position signal voltage, DTC P0405 will set.

Conditions for Running the DTC

The vehicle is operating on CNG.

Conditions for Setting the DTC
    • The EGR valve position signal voltage is less than 0.09 volts.
    •  The condition exists for more than 5 seconds.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/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. This step verifies that a condition does not exist with the EGR valve 5 volt reference circuit. If DTC P1635 is set, refer to that diagnostic procedure first.

    2.

  2. This step verifies that the condition is present.

    3.

  3. This step tests the 5 volt reference circuit of the EGR valve. If the DMM does not display 5 volts, test the circuit for an open.

    4.

  4. This step tests the signal circuit of the EGR valve. The scan tool should display 5 volts with the jumper wire installed.

    5.

  5. This step determines if the EGR valve is the cause of the concern. If the scan tool displays 5 volts in both data lists, inspect for poor connections at the EGR valve.

    6.

  6. This step verifies that the alternative fuels ECM is not the cause of the condition.

DTC P0405

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Alternative Fuels (Engine Controls)

2

  1. Turn ON the ignition, with the engine OFF.
  2. With a scan tool, establish communication with the PCM.
  3. Observe the diagnostic trouble code (DTC) information.

Does the scan tool display DTC P1635?

--

Go to DTC P1635 in Engine Controls in the C/K Pickup Service Manual

Go to Step 3

3

  1. With a scan tool, establish communication with the alternative fuels ECM.
  2. Observe the EGR position sensor voltage parameter.

Does the scan tool indicate that the EGR position sensor voltage is less than the specified value?

0.09 V

Go to Step 5

Go to Step 4

4
  1. Observe the Freeze Frame and/or the Failure records data for this DTC.
  2. Turn the ignition OFF 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 and/or the Failure records data.
  5. Monitor the Alternative Fuels ECM DTC information with a scan tool.

Does the DTC fail this ignition cycle?

--

Go to Step 5

Go to Intermittent Conditions

5

  1. Turn OFF the ignition.
  2. Disconnect the harness connector of the EGR valve.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the 5-volt reference circuit of the EGR position sensor with a DMM.

Does the DMM display a voltage near the specified value?

5 V

Go to Step 6

Go to Step 11

6

  1. Turn OFF the ignition.
  2. Connect a fused jumper wire between the 5-volt reference circuit and the signal circuit of the EGR position sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the EGR position sensor voltage parameter from the following modules:
    5. • Alternative Fuels ECM
    • PCM

Does the scan tool indicate that the EGR position sensor voltage is at the specified value in both data lists?

0 V

Go to Step 9

Go to Step 7

7

Does the scan tool indicate that the EGR position sensor voltage is at the specified value in both data lists?

5 V

Go to Step 13

Go to Step 8

8

Test the signal circuit of the EGR for an open between the Alternative Fuels ECM and the splice. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 14

9

  1. Turn OFF the ignition.
  2. Disconnect the alternative fuels ECM connector C002. Refer to Alternative Fuels Engine Control Module Replacement .
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, establish communication with the PCM.
  5. Observe the EGR position sensor voltage parameter.

Does the scan tool indicate that the EGR position sensor voltage is near the specified value?

5 V

Go to Step 17

Go to Step 10

10

Test the signal circuit of the EGR pintle position for a short to ground, or a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 16

11

Test the 5-volt reference circuit of the EGR position sensor for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 12

12

Inspect for proper connections at the harness connector of the PCM . Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 16

13

Inspect for proper connections at the harness connector of the EGR valve . Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 15

14

Inspect for proper connections at the harness connector of the Alternative Fuels ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 17

15

Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement in Engine Controls in the C/K Pickup Service Manual.

Did you complete the replacement?

--

Go to Step 18

--

16

Important: KL6 models require a switchover to gasoline with a scan tool in order to perform the Crankshaft Position Variation Learn Procedure.

KL8 models do not require the Crankshaft Position Variation Learn Procedure.

Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls in the C/K Pickup Service Manual.

Did you complete the replacement?

--

Go to Step 18

--

17

Replace the alternative fuels ECM. Refer to Alternative Fuels Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 18

--

18
  1. Use the scan tool in order to clear the DTCs from the following control modules:
    2. • Alternative Fuels ECM
    • PCM
  2. Turn OFF the ignition for 30 seconds.
  3. 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, select Capture Info in order to observe the stored information.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK