GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2006 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Engine 🢒 Engine Controls - 7.8L 🢒 Turbocharger System Diagnosis

Circuit Description

The variable nozzle turbocharger (VNT) control solenoid valve is located in the turbocharger. The VNT control solenoid valve is controlled by the engine control module (ECM). The VNT control solenoid valve has a 12-volt reference circuit and a VNT control circuit. The ECM supplies voltage to the VNT control solenoid on the 12-volt reference circuit. The VNT control solenoid valve is controlled by the time of voltage supply from the ECM to the VNT control solenoid valve. When the time of voltage supply increases, the VNT control solenoid valve position decreases.

Diagnostic Aids

If any intermittent condition is suspected, the following may cause an intermittent:

    • Poor connections
    • A misrouted harness
    • Rubbed through wire insulation
    • Broken wire inside the insulation
    • Poor connection at the ECM--Inspect the harness connector for the following conditions:
       - Backed-out terminals
       - Improper mating
       - Broken locks
       - Improperly formed or damaged terminals
       - Poor terminal to wire connection
       - Damaged harness--Inspect the wiring harness for damage. If the harness appears to be OK, observe the Current VNT Position display on the scan tool while moving the connectors and the wiring harness related to the sensor. A change in the display will indicate the location of the fault.

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Turn OFF ignition for 30 seconds.
  2. Start the engine.
  3. Monitor the DTC information with a scan tool.

Is DTC P2007, P2008, P2564, P2565, or P2900 also set?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 3

3
  1. Inspect the following for damage and leakage:
    2. • The intake pipe
    • The charge air cooler
    • The boost pressure sensor
    • The EGR valve
  2. Repair as necessary.

Did you find and correct the condition?

--

Go to Step 4

--

4
  1. Observe the TC vane position.
  2. Connect the scan tool.
  3. Turn ON the ignition.
  4. Perform the actuator test for TC vane position sensor with a scan tool.
  5. Observe the TC vane position?

Did the TC vane position operate through the entire specified range?

0-100%

Go to Step 5

Go to Step 8

5
  1. Test the signal circuit between the engine control module (ECM) and the vane position sensor for a short to voltage circuit.
  2. Repair the circuits as necessary.

Did you find and correct the condition?

--

Go to Step 6

Go to Step 7

6
  1. Observe the TC vane position.
  2. Connect the scan tool.
  3. Turn ON the ignition.
  4. Perform the actuator test for TC vane position sensor with a scan tool.
  5. Observe the TC vane position?

Did the TC vane position operate through the entire specified range?

0-100%

Go to Step 7

Go to Step 12

7

Replace the turbocharger vane position sensor. Refer to Turbocharger Vane Position Sensor Replacement .

Did you complete the replacement?

--

Go to Step 8

--

8
  1. Observe the TC vane position.
  2. Connect the scan tool.
  3. Turn ON the ignition.
  4. Perform the actuator test for TC vane position sensor with a scan tool.
  5. Observe the TC vane position?

Did the TC vane position operate through the entire specified range?

0-100%

Go to Step 12

Go to Step 9

9

Replace the turbocharger assembly. Refer to Turbocharger Replacement .

Did you complete the replacement?

--

Go to Step 10

--

10
  1. Observe the TC vane position.
  2. Connect the scan tool.
  3. Turn ON the ignition.
  4. Perform the actuator test for TC vane position sensor with a scan tool.
  5. Observe the TC vane position?

Did the TC vane position operate through the entire specified range?

--

Go to Step 12

Go to Step 11

11

Important: The replacement ECM must be programmed.

Replace the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data or Fuel Injector Flow Rate Programming .

Did you complete the replacement?

--

Go to Step 12

--

12

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2