GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Blazer - 4WD 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 Transfer Case Shift Control Switch Indicator Always On - Two or More

Circuit Description

The indicator lamps circuit consist of 5 individual lamps contained inside the mode/range switch assembly. They are AUTO 4WD, 2HI, 4HI, 4LO and Neutral. The AUTO 4WD, 2HI, 4HI, and 4LO lamps are contained inside their respective mode button. When the ignition in ON, the transfer case shift control module illuminates the indicator lamp that corresponds to the current ATC gear position by providing a ground through a current limiting driver.

The transfer case shift control module flashes each indicator lamp after a shift has been requested and continues to flash until the transfer case shift control module completes the shift.

A solid state circuit located inside the switch supplies ignition voltage to the lamps. The solid state circuit also receives voltage when the headlamp switch is in the parklamp or headlamp position. When the solid state circuit receives voltage from the headlamp switch it reduces the voltage that it supplies to the indicator lamps, dimming the lamps when the headlamps are ON.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests the transfer case electrical control of the lamp circuits.

    2.

  2. This step helps determine a short to ground in the suspect lamp circuits.

    3.

  3. This step tests the suspect lamp circuits for a short to ground.

    4.

  4. This step repairs a short to ground in the suspect lamp circuit.

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. Turn the ignition ON, with the engine OFF.
  2. Install a scan tool.
  3. Using a scan tool, command all the indicator lamps OFF.

Do all the indicator lamps go OFF?

Go to Step 7

Go to Step 3

3

  1. Use the scan tool in order to determine which mode the transfer case is in.
  2. Use this information to determine which lamp circuit is at fault.
  3. Disconnect the range/mode switch.
  4. Test the suspect lamp circuits for a short to ground. Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Is the suspect circuits shorted to ground?

Go to Step 4

Go to Step 6

4

  1. Disconnect the transfer case shift control module.
  2. Test the suspect lamp circuits for a short to ground. Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Is the suspect circuits shorted to ground?

Go to Step 5

Go to Step 7

5

Repair short to ground in the suspect lamp circuit. Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 8

--

6

Replace the transfer case shift control switch. Refer to Transfer Case Shift Control Switch Replacement .

Did you complete the repair?

Go to Step 8

--

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
  1. Use the scan tool in order to clear the DTCs .
  2. Operate the vehicle in order to determine if the symptom has been corrected.

Is the symptom still present?

Go to Step 2

System OK