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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1028 (Transfer Case - NVG 261-NP2) >> Diagnostic Information and Procedures >> Four-Wheel Drive Does Not Engage >> Test Description

Test Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers on the diagnostic table.

  1. 2:  Tests for proper ignition 3 voltage to the front axle actuator.
  2. 3:  Tests for proper ground at the front axle actuator.
  3. 4:  Tests for proper ground at the axle actuator control circuit through the transfer case switch.
  4. 5:  Tests the transfer case switch ground circuit for an open.
  5. 6:  Tests the transfer case switch for proper operation.
Four-Wheel Drive Does Not Engage

Step Action Values Yes No
Schematic Reference: Transfer Case Control Schematics 
1 Did you perform a Diagnostic System Check-Transfer Case? - Go to Step 2  Go to Diagnostic System Check - Transfer Case 
2 
  1. Turn OFF the ignition.
  2. Disconnect the front axle actuator.
  3. Ensure the 4-wheel drive (4WD) control lever is in the 4WD position.
  4. Turn ON the ignition with the engine OFF.
  5. Test the ignition 3 voltage circuit for proper voltage.
Does the voltage measure within the specified value?		 9-14 V Go to Step 3  Go to Step 7 
3 
  1. Disconnect the front axle actuator.
  2. Turn ON the ignition, with the engine OFF.
  3. Measure the voltage between the ignition 3 voltage circuit and the ground circuit at the front axle actuator.
Does the voltage measure within the specified value?		 9-14 V Go to Step 4  Go to Step 8 
4 
  1. Turn ON the ignition, with the engine OFF.
  2. Shift the transfer case into 4HI.
  3. Connect a test lamp between the ignition 3 voltage circuit and the axle actuator control circuit, at the front axle actuator.
Does the test lamp illuminate?		 - Go to Step 11  Go to Step 5 
5 
  1. Disconnect the transfer case switch.
  2. Connect a test lamp from the ignition 3 voltage circuit to the transfer case switch ground circuit
Does the test lamp illuminate?		 - Go to Step 6  Go to Step 9 
6  With the control lever in the 4WD position, test for continuity across the transfer case switch.
Is continuity present across the switch?		 - Go to Step 10  Go to Step 12 
7 Repair the open in the ignition 3 voltage circuit. Refer to Circuit Testing , and to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 13  -
8 Repair the open in the ground circuit. Refer to Circuit Testing , and to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 13  -
9 Repair the open in the transfer case switch ground circuit. Refer to Circuit Testing , and to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 13  -
10 Repair the open in the axle actuator control circuit. Refer to Circuit Testing , and to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 13  -
11 Replace the front axle actuator. Refer to Electric Motor Actuator Replacement in Front Drive Axle.
Did you complete the replacement?		 - Go to Step 13  -
12 Replace the transfer case switch. Refer to Transfer Case Gear Indicator Switch Replacement .
Did you complete the repair?		 - Go to Step 13  -
13 Operate the vehicle in order to determine if the symptom has been corrected.
Is the symptom still present?		 - Go to Step 2  System OK
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