GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The transfer case shift control module controls the Transfer Case Lock Solenoid.

The lock is energized (locking action released, grounding the Lock Control Circuit) during gear shifts and in AUTO 4WD mode of operation. When power or ground is removed from the lock solenoid, (locking action applied), the transfer case motor is prevented from moving. In this manner, the system is capable of providing a 4H and 4L lock-up without the need of additional vehicle power to hold the transfer case in these positions.

This DTC detects an open lock control circuit or an open Lock feed.

Conditions for Setting the DTC

    • The system will try to turn the lock solenoid off by opening the ground circuit.
    • If the module is unable to de-energize the solenoid, the system will not attempt to de-energize the solenoid again during that ignition cycle.
    •  Transfer Case Lock output reads back as a low voltage when a high voltage is expected.

Action Taken When the DTC Sets

    • All shifting will be disabled.
    • The SERVICE 4WD indicator will be latched on 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 no longer exists.
    • 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. Measures for proper voltage on the lock feed circuit.

  2. Measures the resistance through the lock control solenoid.

  3. Measures for a short to ground in the transfer case lock solenoid.

  4. Tests the Transfer Case Lock circuit for a short to ground.

  5. Tests the Transfer Case Lock circuit for an open.

  6. Repairs the Brake Feed circuit for an open.

Step

Action

Value(s)

Yes

No

Schematic Reference: Transfer Case Control Schematics

1

Was the Transfer Case Diagnostic System Check performed?

--

Go to Step 2

Go to Diagnostic System Check - Transfer Case

2

  1. Turn the ignition OFF.
  2. Disconnect the encoder motor.
  3. Turn the ignition ON, with the engine OFF.
  4. Probe the Lock Feed circuit of the encoder motor with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 3

Go to Step 7

3

Measure the resistance across the encoder motor lock control using a Digital Multimeter DMM.

Is the resistance reading within the specified value?

20-80 ohms

Go to Step 4

Go to Step 8

4

At the transfer case side of the 4 pin connector, with a DMM measure the transfer case lock circuit for a short to ground.

Was a short to ground found?

-

Go to Step 8

Go to Step 5

5

  1. Disconnect the transfer case shift control module connectors.
  2. Use a DMM to check the Transfer Case Lock circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Was the condition found and corrected?

--

Go to Step 10

Go to Step 6

6

Test the Transfer Case Lock circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Was the condition found and corrected?

--

Go to Step 10

Go to Step 9

7

Check the lock feed and lock solenoid control circuits for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Was the condition found and corrected?

--

Go to Step 10

Go to Step 9

8

Replace the encoder motor. Refer to Transfer Case Motor/Encoder Replacement .

Is the repair complete?

--

Go to Step 10

--

9

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

Is the repair complete?

--

Go to Step 10

--

10

  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