GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Astro - 4WD 🢒 DTC 🢒 DTC C0300

Circuit Description

The rear propshaft speed sensor is a permanent magnet generator. The permanent magnet generator produces a pulsing AC voltage. The AC voltage level and number of pulses increases 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.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC C0300 Rear Speed Sensor Malfunction

Conditions for Running the DTC
    • The ignition is ON.
    • The system voltage is 9-16 volts.
    • The vehicle speed must be greater than 16 km/h (10 mph).
    • The transmission is not in Park/Neutral.
    • The engine is running.
    • The front axle is engaged.

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.

Action Taken When the DTC Sets
    • All Shifts to AUTO 4WD mode are disabled. If the current mode is AUTO 4WD, the system does not allow any further adaptive events, such as correcting wheel 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 speed sensor low circuit for a short to ground, a high resistance, or an open.

    5.

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

    6.

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

    7.

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

    8.

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

Step

Action

Value(s)

Yes

No

Schematic Reference: Transfer Case Control Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Drive the vehicle for a short test drive.
  2. While driving, use a scan tool in order to observe the value of the Rear Propshaft Speed parameter.

Does the RPM value vary while driving at a steady speed?

--

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. With a DMM measure the resistance of the transfer case rear propshaft speed sensor.

Is the resistance reading within the specified values?

1300-2700 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. Refer to Lifting and Jacking the Vehicle in General Information.
  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 speed sensor low circuit for the following conditions:
    3. • Short to ground
    • High resistance
    •  An open
    • Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find an correct the condition?

--

Go to Step 12

Go to Step 6

6

Test the rear speed sensor high circuit for the following conditions:

    • Short to ground
    • High resistance
    •  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 rear speed sensor high circuit for a short to voltage. Refer to Testing for a Short to Voltage and Wiring Repairs in Wiring Systems.

Did you find an correct the condition?

--

Go to Step 12

Go to Step 8

8

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

Did you find an correct the condition?

--

Go to Step 12

Go to Step 9

9

Test the rear speed sensor high circuit for a short to the rear speed sensor low 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 rear propshaft speed sensor. Refer to Transfer Case Speed Sensor Replacement .

Did you complete the repair?

--

Go to Step 12

--

11

Replace the transfer case shift control module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

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 reset?

--

Go to Step 2

System OK