For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle Prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### Circuit Description

The Isuzu T150 transfer case contains a 2/4 wheel indicator switch and a separate neutral switch. Each switch is provided 12 volts on the signal circuit by the transfer case shift control module. A separate ground circuit is provided to both switches. A fault in the 2WD/4WD signal circuit or the neutral switch signal circuit will cause the 4WD high or 4WD low mode indicator to flash. Also, a fault in the front axle actuator or actuator circuits can cause the 2WD mode indicator to flash. In 2WD mode, the 2/4 wheel indicator switch and the neutral switch are open and the signal circuits are at B+. In 4WD high or low mode, the transfer case 2/4 wheel indicator switch is closed, and the neutral switch is open.

### Diagnostic Aids

A low battery condition or charging system that is faulty could produce this fault. Refer to Battery Inspection/Test and Charging System Test .

### Reference Information

#### Schematic Reference

Transfer Case Control Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Transfer Case Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Ignition ON, select the 4WD high and low mode button one at a time. The mode indicator on the 4WD high and low button, should be ON steady, after the shift is completed.
2. If the vehicle passes the Circuit/System Verification, then refer to Testing for Intermittent Conditions and Poor Connections .

### Circuit/System Testing

1. Ignition ON, engine OFF. Set the parking brake.
2. Shift the transfer case to 4WD high and the transmission into neutral.
3. Raise the vehicle on a hoist.
4. With a scan tool, command the front axle actuator to engage. While spinning a front tire, the front propshaft should turn.

⇒ | If the front propshaft does not spin, refer to Front Axle Will Not Engage .

5. Ignition OFF, disconnect the transfer case 2/4 wheel indicator switch electrical connector.
6. Ignition OFF, verify that a test lamp illuminates between B+ and terminal 2 of the transfer case 2/4 wheel indicator switch connector.

⇒ | If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

7. Ignition ON, with a DMM measure for 10-12 volts on terminal 1 of the transfer case 2/4 wheel indicator switch connector and ground.

⇒ | If the voltage is not within the specified range, test the 2WD/4WD signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the transfer case shift control module.

8. Ignition OFF, disconnect the transfer case neutral switch electrical connector.
9. Ignition OFF, verify that a test lamp illuminates between B+ and terminal 2 of the transfer case neutral switch.

⇒ | If the test lamp does not illuminate test the ground circuit for an open/high resistance.

10. Ignition ON, with a DMM measure for 10-12 volts on terminal 1 on the transfer case neutral switch and ground.

⇒ | If the voltage is not within the specified range, test the neutral switch signal circuit for a short to ground, or an open/high resistance. If the circuit tests normal, replace the transfer case shift control module.

### Component Testing

Important: You must perform the Circuit/System Testing first.

1. Ignition OFF, remove the transfer case 2WD/4WD wheel indicator switch from the transfer case.
2. Connect a DMM across terminals 1 and 2 on the switch. Measure for less than 1 ohm of resistance with the switch plunger depressed.

⇒ | If the resistance is more than the specified value, replace the transfer case 2WD/4WD wheel indicator switch.

3. Remove the transfer case neutral switch from the transfer case.
4. Connect a DMM across terminals 1 and 2 on the switch. Measure for less than 1 ohm of resistance with the switch plunger depressed.

⇒ | If the resistance is more than the specified value, replace the transfer case neutral switch.

5. Test for continuity on the transfer case neutral switch between terminal 1 and the switch housing and also between terminal 2 and the switch housing.

⇒ | If continuity is detected, replace the transfer case neutral switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Control Module References for control module replacement, setup, and programming

• | Transfer Case Neutral Switch Replacement

• | Transfer Case 2/4 Indicator Switch Replacement