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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2007 🢒 Escalade 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 DTC C0306

Circuit Description

The transfer case motor is a bi-directional, permanent magnet, DC motor. When energized, through motor control A or motor control B, the ground is provided by the opposing motor control circuit and then grounded through the transfer case shift control module ground circuit, the motor, through a series of gears, rotates a shaft which moves the mode and range forks to shift the transfer case between the following ranges:

    • 2HI
    • 4HI
    • 4LO
    • AUTO 4WD
    • Neutral

This DTC detects an open, short to voltage, or short to ground in the motor control A or motor control B circuits, or an open, or short to ground inside the motor.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC C0306 05: Motor A or B Circuit Short to Battery or Open

DTC C0306 02: Motor A or B Circuit Short to Ground

Diagnostic Fault Information

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Motor A or B Circuit

C0306 02

C0306 05

C0306 05

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Conditions for Running the DTC
    • The ignition is ON.
    • The system voltage is 9-18 volts.

Conditions for Setting the DTC
    • The system tests the motor circuits by checking for unwanted voltage.
    • Then, the system supplies voltage on each of the motor circuits and reads the voltage back on the other circuit.
    • If the system detects a condition with the circuits, the DTC is logged. The transfer case shift control module senses a low voltage return in the motor control A or motor control B circuits when a high voltage is expected.
    • The fault must remain current for 30 seconds to set the DTC.

Action Taken When the DTC Sets
    • All shifting is disabled.
    • The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.
    • The transfer case shift control module provides a reference voltage of 4.5 volts on the motor A/B line for diagnostic purposes.

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 the battery positive and ground circuits for poor connections.

    2.

  2. This step tests the encoder motor for an internal short to ground.

    3.

  3. This step helps isolate motor malfunctions from the transfer case shift control module and wiring.

    4.

  4. This step tests for an open, high resistance, short to ground or short to voltage.

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 - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Check the battery positive and ground circuits at the transfer case shift control module for poor connections. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 8

Go to Step 3

3

Important: Use test leads designed for this connector and make firm contact with the leads.

  1. Turn off the ignition.
  2. Disconnect the encoder motor.
  3. With a DMM at the encoder motor pigtail connector, test motor control A and motor control B for a short to ground within the encoder motor.

Is motor control A or motor control B shorted to ground?

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Go to Step 6

Go to Step 4

4

    Important: Use test leads designed for this connector and make firm contact with the leads.

  1. Turn OFF the ignition.
  2. Disconnect the encoder motor connector.
  3. Zero the DMM with ohms selected by touching the 2 leads.
  4. Connect the DMM between motor control A terminal and motor control B terminal and test the resistance in the encoder motor.

Is the motor/encoder within the specified values?

0.3-35 ohms

Go to Step 5

Go to Step 6

5

  1. Disconnect the transfer case shift control module connectors C1 and C2.
  2. Test the motor A and motor B control circuits for a short to ground, a short to voltage, an open, or a high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 8

Go to Step 7

6

Replace the encoder motor. Refer to Transfer Case Encoder Motor Replacement . Perform the Clutch Reset Procedure. Refer to Transfer Case High/Low Clutch Reset .

Did you complete the repair?

--

Go to Step 8

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7

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 Control Module References for replacement, setup, and programming. Perform the Clutch Reset Procedure. Refer to Transfer Case High/Low Clutch Reset .

Did you complete the repair?

--

Go to Step 8

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8
  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