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Home >> Hummer >> 2008 >> H2 4D Utility Wagon >> Repair and Diagnosis >> Drivelines & Axles >> Differentials & Drive Axles >> Rear Drive Axle >> Diagnostic Information and Procedures >> Electronic Rear Differential Lock Will Not Engage >> Test Description

Test Description

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

  1. 2:  This step determines if the fault is present or intermittent.
  2. 3:  This step determines if the transfer case shift control module is receiving a differential lock request from the transfer case shift control switch.
  3. 4:  This step determines if a bad switch is causing the symptom.
  4. 5:  This step determines if a short, open, or high resistance in the 5-volt reference or switch signal circuits is causing the symptom.
  5. 6:  This step determines of the coil has excessive resistance or if the windings are shorted together.
  6. 7:  This step determines if the coil or pigtail is shorted to ground.
  7. 8:  This step determines if either the differential lock control or differential lock return circuits are shorted to ground.
  8. 9:  This step tests for an open or high resistance in both the return and control circuits.
  9. 10:  This step refers to transfer case shift control module replacement.
  10. 11:  This step refers to encoder motor replacement.
  11. 12:  This step replaces the transfer case shift control switch.
Step Action Value (s) Yes No
Schematic Reference:  Differential Lock Schematics  
Connector End View Reference:  Component Connector End Views 
1 Did you perform the Diagnostic System Check - Vehicle? - Go to Step 2  Go to Diagnostic System Check - Vehicle
2  Verify the fault is present.
Perform the Locking Differential functional check. Refer to Locking Differential Diagnosis 
Does the system operate normally?		 - Go to Testing for Intermittent Conditions and Poor Connections Go to Step 3 
3  While observing the rear axle lock request on the scan tool, request the rear differential lock ON by pressing the rear differential lock button.
Does the scan tool indicate rear axle lock ON?		 - Go to Step 6  Go to Step 4 
4 
  1. With a DMM, check the resistance of the transfer case shift control switch.
  2. While depressing and holding the differential lock button, probe the 5-volt reference and switch signal circuit pins on the back of the switch.
Is the switch within the specified value?		 64.25-65.55 Ω Go to Step 5  Go to Step 12 
5  Check the 5-volt reference and switch signal circuits for an open, short, or high resistance between the transfer case shift control switch, and the transfer case shift control module. Refer to Circuit Testing and Wiring Repairs .
Was the condition found and corrected?		 - Go to Step 13  Go to Step 6 
6 
  1. Disconnect the rear differential lock harness from the rear differential lock coil pigtail.
  2. With a DMM, measure the resistance of the rear differential lock coil and pigtail by probing the rear differential lock return and the rear differential lock control circuits.
Was the resistance reading within the specified values?		 2.2-4.3 Ω Go to Step 7  Go to Step 11 
7  With the connector still disconnected, with a DMM, probe the return then the control circuits and check for resistance to ground.
Did the DMM indicate a short to ground?		 - Go to Step 11  Go to Step 8 
8 
  1. Disconnect the C1 from the transfer case shift control module.
  2. Disconnect the rear differential lock harness from the rear differential coil pigtail.
  3. Turn the ignition ON.
  4. With a DMM, check for a short to power or short to ground on the differential lock control and differential lock return circuits. Refer to Circuit Testing and Wiring Repairs .
Was the condition found and corrected?		 - Go to Step 13  Go to Step 9 
9  Check the differential lock control and differential lock return circuits for an open or high resistance. Refer to Circuit Testing and Wiring Repairs .
Was the condition found and corrected?		 - Go to Step 13  Go to Step 10 
10  Replace the transfer case shift control module. Refer to Control Module References for replacement, setup, and programming.
Was the repair completed?		 - Go to Step 13  -
11  Replace the electronic locking differential locking mechanism and/or side gear. Refer to Locking Differential Disassemble  and Locking Differential Assemble .
Was the repair completed?		 - Go to Step 13  -
12  Replace the transfer case shift control switch. Refer to Transfer Case Shift Control Switch Replacement .
Was the repair completed?		 - Go to Step 13  -
13
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for allowing the symptom to occur.
Does the symptom occur?		 - Go to Step 1  System OK
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