GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 HUMMER 🢒 2007 🢒 H3 🢒 Driveline/Axle 🢒 Rear Drive Axle 🢒 Electronic Rear Differential Lock Will Not Engage

Circuit Description

The rear differential control circuit consists of an actuator which engages and disengages the rear axle differential lock. The rear differential actuator consists of a coil assembly, and a locking assembly with springs and pins to lock the rear differential, all within the rear differential assembly.

The rear axle differential lock actuator consists of the following circuits:

    • The rear differential lock control circuit, which is connected to the transfer case shift control module and supplies battery voltage.
    • The rear differential lock return ground circuit, which is also connected to the transfer case shift control module.

Whenever the rear differential lock has been requested the transfer case shift control module provides battery voltage through the rear differential lock control circuit, and provides ground through the rear differential lock return circuit through a current limiting driver.

Whenever a rear differential lock is requested the transfer case must be in 4LO and the vehicle speed must be below 5 km/h (3 mph) for the request to be accepted. The rear differential lock will remain locked up to 32 km/h (20 mph) after which the rear differential lock will disengage.

Test Description

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

  1. This step determines if the fault is present or intermittent.

    2.

  2. This step determines if the transfer case shift control module is receiving a differential lock request from the transfer case shift control switch.

    3.

  3. This step determines if a bad switch is causing the symptom.

    4.

  4. This step determines if a short, open, or high resistance in the 5-volt reference or switch signal circuits is causing the symptom.

    5.

  5. This step determines of the coil has excessive resistance or if the windings are shorted together.

    6.

  6. This step determines if the coil or pigtail is shorted to ground.

    7.

  7. This step determines if either the differential lock control or differential lock return circuits are shorted to ground.

    8.

  8. This step tests for an open or high resistance in both the return and control circuits.

    9.

  9. This step refers to transfer case shift control module replacement.

    10.

  10. This step refers to encoder motor replacement.

    11.

  11. This step replaces the transfer case shift control switch.

Step

Action

Value (s)

Yes

No

Schematic Reference: Differential Lock Schematics

Connector End View Reference: Rear Axle 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 ohms

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 ohms

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