GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Colorado Pickup - 4WD 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 Accessory Switch Transfer Case Mode Indicator Flashes in 2WD Mode

Circuit Description

The Isuzu T150 transfer case contains a 2WD/4WD switch, which is supplied battery voltage by the transfer case shift control module. When the transfer case mode selection is in either 4WD low or 4WD high the 2WD/4WD switch provides a path to ground, pulling the 2WD/4WD signal circuit low. This assists the transfer case shift control module in determining the present mode. A fault in the 2WD/4WD signal circuit, or the neutral switch signal circuit will cause the 2WD mode indicator to flash. A fault in the front axle actuator or the corresponding front axle actuator circuits can also cause the 2WD mode indicator to flash. In the 2WD mode the switch is open and the voltage on the 2WD/4WD signal circuit is battery voltage.

Diagnostic Aids
    • Check the inline connector C105 for proper connection, bent pins, damage, or corrosion. Refer to Harness Routing Views and Delphi Connectors in Wiring Systems.
    • Check the transfer case shift control module connectors C1 and C2 for proper connection and bent or corroded pins or terminals. Refer to Repairing Connector Terminals in Wiring Systems.
    • Check for water leaks at doors and bulkhead areas. Refer to Waterleak Test Preparation .
    • Check the 2WD/4WD switch for proper connection, bent pins, or damaged terminals. Refer to Transfer Case Control Component Views .

Test Description

The number below refers to the step number on the diagnostic table.

  1. This step determines if the front axle actuator is causing the symptom.

    2.

  2. This step determines if a short to ground on the 2WD/4WD switch signal circuit is causing the symptom.

    3.

  3. This step determines if a short to ground on the neutral switch signal circuit is causing the symptom.

Step

Action

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?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Set the parking brake.
  2. Turn the ignition ON with the engine OFF.
  3. Shift the transfer case into 2WD.
  4. Shift the transmission into neutral.
  5. Raise the vehicle on a hoist. Refer to Lifting and Jacking the Vehicle in General Information.
  6. With a scan tool command the front axle actuator to disengage.
  7. With the vehicle on the hoist spin the front tires.

Does the front propshaft turn when the front tires are spun?

Go to Front Axle Will Not Disengage

Go to Step 3

3
  1. Raise the vehicle on a hoist. Refer to Lifting and Jacking the Vehicle in General Information.
  2. Disconnect the transfer case 2WD/4WD switch and remove the switch.
  3. Turn ON the ignition.
  4. Connect the transfer case 2WD/4WD switch and depress the plunger.

Does the 2WD indicator light continue to flash?

Go to Step 4

Go to Transfer Case Assembly Replacement

4

Disconnect the transfer case 2WD/4WD switch.

While in 2WD mode does the 2WD indicator light continue to flash?

Go to Step 5

Go to Transfer Case 2/4 Indicator Switch Replacement

5

Disconnect C2 on the module and the 2WD/4WD switch and test the 2WD/4WD signal circuit for a short to ground. Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 8

Go to Step 6

6

Disconnect the neutral switch and test the neutral switch signal circuit for a short to ground. Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 8

Go to Step 7

7

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 8

--

8

Operate the vehicle in order to determine if the symptom has been corrected.

Is the symptom still present?

Go to Step 1

System OK