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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> Drivelines & Axles >> Differentials & Drive Axles >> Front Drive Axle - 4WD >> System Tests >> Test B: Automatic Four-Wheel Drive Does Not Engage (A4WD)

Test B: Automatic Four-Wheel Drive Does Not Engage (A4WD)

  1. See SYMPTOM INDEX (BLAZER - JIMMY CANADIAN, JIMMY, SONOMA & S10 PICKUP)  table. If you were sent here from the symptom index table, go to next step. If you were not sent here from the symptom index table, go to DIAGNOSTIC STARTING POINT .
  2. Start the engine. Inspect the instrument panel to see if the Service 4WD light is illuminated. If Service 4WD light stays illuminated with engine running, see appropriate TRANSFER CASES article in TRANSMISSION. If Service 4WD light does not stay on with engine running, go to next step.
  3. Inspect the vacuum hoses for kinks, plugged line, damage or a disconnected line. If any vacuum hoses were damaged, go to next step. If no damage was found, go to step  5.
  4. Repair or replace the vacuum hoses as necessary. If front axle engages after repairs are made, system is okay. If front axle does not engage after repairs are made, go to next step.
  5. Press the 4HI button to attempt to engage the front drive axle. Disconnect the vacuum hose from the vacuum actuator. Inspect for vacuum at the vacuum actuator. If there is a vacuum leak at actuator connection, go to next step  6.
  6. Replace the vacuum actuator. See ACTUATOR ASSEMBLY . After repair, if front drive axle engages, system is okay. If front axle does not engage, go to next step.
  7. Replace the vacuum actuator solenoid valve. See VACUUM ACTUATOR SOLENOID VALVE REPLACEMENT  under REMOVAL & INSTALLATION. After repair, if front drive axle engages, system is okay. If front axle does not engage, go to next step.
  8. Inspect the clutch cable for damage, binding or a disconnection. If problem was found, go to next step. If problem was not found, go to step  10.
  9. Replace the clutch cable. See CLUTCH CABLE REPLACEMENT . After repair, if front axle engages, system is okay. If front axle does not engage, go to next step.
  10. Disconnect the clutch cable from the clutch fork. Inspect the operation of the clutch fork using Hub Engagement Tool (J-33798). If front axle engages, system is okay. If front axle does not engage, go to next step.
  11. Replace the clutch fork. See CLUTCH FORK REPLACEMENT  under REMOVAL & INSTALLATION. If front axle engages, system is okay. If front axle does not engage, go to next step.
  12. The cause of concern may be in the front drive axle. Disassemble the front drive axle. Inspect for damaged components and repair as necessary. See DIFFERENTIAL CARRIER  under OVERHAUL.
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