GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 GMC Sierra Denali 🢒 Body 🢒 Data Link Communications 🢒 DTC C0305

Circuit Description

The front 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 increases as speed increases. The transfer case shift control module converts the pulsating AC voltage to a propshaft RPM which is used for the following functions:

    • Calculations
    • To monitor the difference between the front and rear propshaft speed
    • In the AUTO, or the Adapt mode of operation, to determine the amount of slip and the percent of torque to apply to the front axle

The module accesses this input when the vehicle is in AUTO mode, 4HI, and 4LO ranges. 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 front propshaft input indicates a speed of less than 16 RPM for 30 seconds while all of the following are true:

    • Transmission NOT in Park/Neutral
    • Engine is running
    • Front axle is engaged
    • Rear propshaft speed exceeds 512 RPM
    • Vehicle speed on Class 2 Data bus exceeds 16 km/h (10 mph)

Action Taken When the DTC Sets
    • All shifts to AUTO mode are disabled. If the current mode is AUTO, the system does not allow any further adaptive events, such as correcting the slip.
    • The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

Conditions for Clearing the DTC
    • The transfer case shift control module will clear the DTC if the condition for setting the DTC is not currently present.
    • A history DTC will clear 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 front speed sensor low signal circuit for a short to ground, a high resistance, or an open.

    5.

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

    6.

  6. This step tests the front speed sensor low signal circuit for a short to voltage.

    7.

  7. This step tests the front speed sensor high signal circuit for a short to voltage.

    8.

  8. This step tests the front speed sensor low signal circuit for a short to the front speed sensor high circuit.

Step

Action

Values

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. Place the transfer case in AWD mode.
  2. Drive the vehicle for a short test drive.
  3. With the scan tool, observe the value of the Front 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 front 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 front 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 front wheel while rotating the other front wheel.
  6. Observe the AC voltage reading on the DMM.

Is the voltage reading greater than the specified value?

0.2-0.5 V AC

Go to Step 5

Go to Step 10

5

  1. Disconnect the transfer case shift control module.
  2. Test the front 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.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 6

6

Test the front 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.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 7

7

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

Did you find and correct the condition?

--

Go to Step 12

Go to Step 8

8

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

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

9

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

Did you find and correct the condition?

--

Go to Step 12

Go to Step 11

10

Replace the transfer case front propshaft speed sensor. Refer to Transfer Case Front Output Shaft Speed Sensor Replacement .

Did you complete the repair?

--

Go to Step 12

--

11

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

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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