DEFINITION: 4WD does not engage, all other engine and transmission functions are normal.

Did you review the transfer case operation and perform the necessary inspections?

Go to Step 2

Go to Transfer Case Diagnostic System Check

1. Start the engine.
2. Place the transfer case in 4WD and test the vehicle.

Does the 4WD system operate normally?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

1. Test for voltage at the four wheel drive switch signal circuit at the powertrain control module (PCM) connector.
2. Shift the vehicle in and out of 4WD.

Does the voltage fluctuate between 0 and 12 volts when shifting in and out of 4WD?

Go to Step 7

Go to Step 4

Test the four wheel drive switch ground circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 10

Go to Step 5

Test the four wheel drive switch signal circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 10

Go to Step 6

Replace the four wheel drive switch. Refer to Selector Switch Replacement .

Did you complete the replacement?

Go to Step 10

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Test the axle pump ground circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 10

Go to Step 8

Test the axle actuator control circuits for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 10

Go to Step 9

Replace the front drive axle actuator pump. Refer to Electric Motor Actuator Replacement in front axle.

Did you complete the replacement?

Go to Step 10

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Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 3