For 1990-2009 cars

### 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 4WD low or 4WD high mode indicators to flash. A fault in the front axle actuator or the corresponding front axle actuator circuits can also cause the 4WD low or 4WD high mode indicators to flash.

### Diagnostic Aids

• | Check the inline connector C105 for proper connection, bent pins, damage, or corrosion. Refer to Harness Routing Views and Delphi Connectors .

• | 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 .

• | 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. This step determines if the 2WD/4WD switch is causing the symptom.

3. This step determines if an open 2WD/4WD signal circuit is causing the symptom.

4. This step determines if a shorted to ground 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
2 |

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

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

Go to Step 3

Go to Front Axle Will Not Engage

3 |

1. Shift the vehicle to 4WD.
2. Remove the 2WD/4WD switch.
3. With the switch connected depress the plunger.

Does the 4WD indicator light flash?

Go to Step 4

Go to Transfer Case Assembly Replacement

4 | With a fused jumper wire short the 2WD/4WD signal circuit to a known good ground. Refer to Using Fused Jumper Wires and Wiring Repairs . Does the 4WD high mode indicator continue to flash? | Go to Step 5 | Go to Step 7
5 | Test the 2WD/4WD signal circuit for an open. Refer to Testing for Continuity and Wiring Repairs . Did you find and correct the condition? | Go to Step 9 | 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 . Did you find and correct the condition? | Go to Step 9 | Go to Step 8
7 | Replace the 2WD/4WD switch. Refer to Transfer Case 2/4 Indicator Switch Replacement . Did you complete the repair? | Go to Step 9 | --
8 | Replace the transfer case shift control module. Refer to Control Module References for replacement, setup, and programming. Did you complete the repair? | Go to Step 9 | --
9 | Operate the vehicle in order to determine if the symptom has been corrected. Is the symptom still present? | Go to Step 1 | System OK