Will Not Engage In Four Wheel Drive

1. Raise vehicle on a suitable lift so that all four wheels are free to rotate, then start engine.
2. Disconnect mode selector vacuum harness at steel tube connection.
3. Using a suitable vacuum gauge, check for vacuum at steel tube that connects to red hose in harness. If vacuum is present, stop engine, then proceed to step 5. If no vacuum is present, refer to next step.
4. Check intake manifold vacuum supply fitting, vacuum hose, and vacuum storage tank. Repair or replace damaged or leaking components. If vacuum leak still exists, check and replace vacuum hose from storage tank to steel tube if necessary. If there is no vacuum leak at this point, and two wheel drive will still not engage, then stop engine and proceed to next step.
5. Connect a suitable vacuum pump to steel tube that connects to yellow hose in harness. Apply 20 inches vacuum and rotate right wheel to engage axle. If front axle does engage, proceed to step 7. If front axle does not engage, refer to next step.
6. Check front axle shift motor operation, refer to "Axle Shift Motor Function Test." If shift motor is operational, check vacuum lines and tubes for leaks or damage, and repair if necessary. If shift motor is inoperative, replace. If axle will still not engage, remove shift housing cover and shift motor, inspect shift fork and collar and axle components, and repair as necessary.
7. Check transfer case shift motor, motor stem should be retracted. If stem is retracted, check transfer case shift linkage and repair if necessary. If motor stem is not retracted, proceed to next step.
8. Check vacuum tubes and lines, repair as necessary. If transfer case shift motor is still inoperative, proceed to next step.
9. Check transfer case shift motor operation. Refer to "Transfer Case Shift Motor Function Test." If transfer case shift motor is inoperative, replace motor and recheck system. If transfer case shift motor is operational and transfer case does not engage, refer to next step.
10. Check axle shift linkage and repair as necessary. Transfer case should then engage in four wheel drive. If case does not engage, repair case as necessary and recheck system.