GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC K Sierra - 4WD (CNG) 🢒 DTC 🢒 DTC P0406

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 high EGR valve position signal voltage, DTC P0406 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 more than 4.9 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 the condition is present.

    2.

  2. This step determines if the signal circuit of the EGR valve is shorted to a voltage.

    3.

  3. This step tests the 5 volt reference circuit of the EGR valve. If the DMM displays above 5 volts, test the circuit for a short to voltage.

    4.

  4. This step tests the low reference circuit of the EGR valve position sensor. If the test lamp does not illuminate, test the circuit for an open.

    5.

  5. This step verifies that the PCM is not the cause of the condition.

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 alternative fuels ECM.
  3. Observe the EGR position sensor voltage parameter.

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

4.9 V

Go to Step 4

Go to Step 3

3
  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 4

Go to Intermittent Conditions

4

  1. Turn OFF the ignition.
  2. Disconnect the harness connector of the EGR valve.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the EGR position sensor voltage parameter with a scan tool.

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

4.9 V

Go to Step 8

Go to Step 5

5

Measure the voltage from the 5-volt reference circuit of the EGR position sensor with a DMM.

Does the DMM display a voltage more than the specified value?

5.2 V

Go to Step 10

Go to Step 6

6

Probe the low reference circuit of the EGR pintle position sensor with a test lamp connected to B+.

Does the test lamp illuminate?

--

Go to Step 12

Go to Step 7

7

Test the low reference of the EGR pintle position sensor for an open. 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 15

Go to Step 11

8

  1. Turn OFF the ignition.
  2. Disconnect the PCM connector C1. Refer to Powertrain Control Module Replacement in Engine Controls in the C/K Pickup Service Manual.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the EGR position sensor voltage parameter with a scan tool.

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

4.9 V

Go to Step 9

Go to Step 13

9

Test the signal circuit of the EGR pintle position for a short to voltage. 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 15

Go to Step 14

10

Test the 5-volt reference circuit of the EGR position sensor for a short to voltage. 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 15

Go to Step 13

11

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 15

Go to Step 13

12

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 15

--

13

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 15

--

14

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

Did you complete the replacement?

--

Go to Step 15

--

15
  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 16

Go to Step 2

16

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