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/System 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 neutral mode indicator to flash. Also, a fault in the front axle actuator or actuator circuits can cause the neutral mode indicator to flash. In neutral mode, the 2/4 wheel indicator switch is open and the neutral switch is closed. In 4WD high, or 4WD low, 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 neutral mode position on the accessory switch. The mode indicator for the neutral position 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 neutral and the transmission into neutral.
3. Raise the vehicle on a hoist.
4. Observe the front propshaft when spinning the front tires. The front propshaft should not turn.

⇒ | If the front propshaft spins, refer to Front Axle Will Not Disengage .

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.

• | Transfer Case Neutral Switch Replacement

• | Transfer Case 2/4 Indicator Switch Replacement

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