GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 Envoy - 4WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 126-NP4 🢒 DTC C0300

Circuit Description

The rear propshaft speed sensor is a permanent magnet (PM) generator. The PM generator produces a pulsing AC voltage. The AC voltage level and number of pulses increase as speed increases. The module converts the pulsating AC voltage to a propshaft RPM which is used for calculations. The propshaft RPM can be displayed with a scan tool.

This DTC detects an open , short to ground, short to voltage or faulty sensor.

Conditions for Running the DTC
    • The ignition is ON.
    • System voltage is 9-18 volts.
    • Vehicle speed exceeds 16 km/h (10 mph).

Conditions for Setting the DTC

The system logs the DTC if the rear propshaft input indicates a speed of less than 16 RPM for 30 seconds while all of the following are true:

    • The transmission is NOT in PARK/NEUTRAL.
    • The engine is running.
    • Vehicle Speed On Class 2 Data bus exceeds 16 km/h (10 mph).

Action Taken When the DTC Sets
    • All shifts to AUTO, Adapt mode are disabled. If the current mode is AUTO, the system does not allow any further adaptive events, correct slip.
    • The SERVICE AWD indicator remains illuminated for the remainder of the current ignition cycle.

Conditions for Clearing the DTC
    • The transfer case shift control module clears the DTC if the condition for setting the DTC no longer exists.
    • A history DTC clears after 100 consecutive ignition cycles without a fault present.
    • History DTCs can be cleared using a scan tool.

Test Description

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

  1. This step tests to see if the malfunction is intermittent.

    2.

  2. This step tests the internal resistance of the propshaft speed sensor.

    3.

  3. This step tests to see if the propshaft speed sensor can generate a sufficient amount of AC voltage.

    4.

  4. This step tests the rear propshaft speed sensor low circuit for a short to ground, a high resistance, or an open.

    5.

  5. This step tests the rear propshaft speed sensor high circuit for a short to ground, a high resistance, or an open.

    6.

  6. This step tests the rear propshaft speed sensor low circuit for a short to voltage.

    7.

  7. This step tests the rear propshaft speed sensor high circuit for a short to voltage.

    8.

  8. This step tests the rear propshaft speed sensor low circuit for a short to the rear propshaft speed sensor high circuit.

Step

Action

Value(s)

Yes

No

Schematic Reference: Transfer Case Control Schematics

Connector End View Reference: Transfer Case Control Connector End Views

1

Did you perform the Diagnostic System Check - Transfer Case?

--

Go to Step 2

Go to Diagnostic System Check - Transfer Case

2

  1. Drive the vehicle for a short test drive.
  2. With the scan tool, observe the value of the Rear Propshaft Speed Data Parameter in the Transfer Case Data List while driving.

Does the RPM value vary while driving?

--

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

  1. Turn the ignition OFF.
  2. Disconnect the transfer case rear propshaft speed sensor.
  3. Measure the resistance of the transfer case rear propshaft speed sensor.

Is the resistance reading within the specified values?

1,300-2,700 ohms

Go to Step 4

Go to Step 10

4

  1. Connect a DMM to the transfer case rear propshaft speed sensor.
  2. Block the front wheels.
  3. Place the transmission in NEUTRAL.
  4. Raise and support the rear axle so that the wheels turn freely.
  5. Hold one rear wheel while rotating the other rear wheel.
  6. Observing the AC voltage reading on the DMM

Is the voltage reading greater than the specified value?

0.5 V AC

Go to Step 5

Go to Step 10

5

  1. Disconnect the transfer case shift control module.
  2. Test the rear propshaft speed sensor low signal circuit for a short to ground, a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Was the condition found and corrected?

--

Go to Step 12

Go to Step 6

6

Test the rear propshaft speed sensor high signal circuit for a short to ground, a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Was the condition found and corrected?

--

Go to Step 12

Go to Step 7

7

Test the rear propshaft speed sensor low signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Was the condition found and corrected?

--

Go to Step 12

Go to Step 8

8

Test the rear propshaft speed sensor high signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Was the condition found and corrected?

--

Go to Step 12

Go to Step 9

9

Test the rear propshaft speed sensor high circuit for a short to the rear propshaft sensor low signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Was the condition found and corrected?

--

Go to Step 12

Go to Step 11

10

Replace the transfer case rear propshaft speed sensor. Refer to Transfer Case Rear Output Shaft Speed Sensor Replacement - Right Side .

Did you complete the repair?

--

Go to Step 12

--

11

Important: After transfer case shift control module replacement and reprogramming, ensure all doors are closed and the key is out of the ignition, then open and close the doors again and wait 2 minutes to avoid incomplete programming or false communication DTCs.

Replace the transfer case shift control module. Refer to Transfer Case Shift Control Module Replacement and Transfer Case Shift Control Module Reprogramming .

Did you complete the repair?

--

Go to Step 12

--

12
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC set?

--

Go to Step 2

System OK