Hummer H2. Manual - part 889

1

or

Go to 

Step 

2

Transfer Case in 

Transfer Case - 

BW4484

2

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 

ohm

Go to 

Step 

3

Go to Step 8

3

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 

8

Go to Step 4

4

1. Disconnect connector C1 from the transfer case shift 

control module.  

2. Disconnect the rear differential lock harness from the 

rear differential coil pigtail.  

3. 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 in Wiring Systems.  

Was the condition found and corrected?

-

Go to 

Step 

9

Go to Step 5

5

Check the differential lock control and the differential lock 
return circuits for being shorted together. Refer to Circuit 
Testing and Wiring Repairs in Wiring Systems.Was the 
condition found and corrected?

IMPORTANT:

This circuit contains a reversed bias diode. The red lead 
of the DMM must be placed on the rear differential lock 
high control circuit, and the black lead on the rear 
differential lock low reference circuit. This is done to 
avoid showing the circuits falsely shorted together.

-

Go to 

Step 

9

Go to Step 6

6

Check the suspect circuit for an open or high resistance. 
Refer to Circuit Testing and Wiring Repairs in Wiring 
Systems. 
Was the condition found and corrected?

-

Go to 

Step 

9

Go to Step 7

7

Replace the transfer case shift control module. Refer to 
Transfer Case Shift Control Module Replacement in 
Transfer Case - BW4484. 
Was the repair completed?

-

Go to 

Step 

9

-

Replace the rear differential lock coil. Refer to Locking 

Go to 

 

2004 Hummer H2 

2004 DRIVELINE/AXLE Drive Axle - Locking/Limited Slip - Hummer H2

  

SYMPTOMS - LOCKING/LIMITED SLIP REAR AXLE 

Review the system and operation in order to familiarize yourself with the system functions. Refer to Locking 
Differential Description and Operation . 

Visual/Physical Inspection 

z

Inspect the system for the following: 

{

Loose or missing fasteners  

{

Obvious damage or conditions which may cause the symptom.  

z

Check the system for proper operation. Refer to Locking Differential Diagnosis .  

Symptom List 

Refer to a system diagnostic procedure from the following list in order to diagnose the symptom: 

z

Electronic Rear Differential Lock Will Not Engage  

z

Electronic Rear Differential Lock Will Not Disengage  

LOCKING DIFFERENTIAL DIAGNOSIS 

1. Block the right front and rear wheels.  

2. Turn the Ignition ON - Do not start the engine.  

3. Place the transmission in NEUTRAL.  

4. Shift the transfer case into 4 LOW.  

5. Engage the differential lock switch.  

6. Raise the left front wheel off the ground. Refer to Lifting and Jacking the Vehicle in General 

Information. 

Support the left front wheel with safety stands. 

7. Raise the left rear wheel off the ground. Refer to Lifting and Jacking the Vehicle in General 

Information. 

Support the left rear wheel with safety stands.

8

Differential Coil Assembly Replacement . 
Was the repair completed?

-

Step 

9

-

9

1. Use the scan tool in order to clear the DTCs.  

2. Operate the vehicle within the Conditions for Running 

the DTC as specified in the supporting text.  

Does the DTC reset?

-

Go to 

Step 

1

System OK

 

2004 Hummer H2 

2004 DRIVELINE/AXLE Drive Axle - Locking/Limited Slip - Hummer H2

  

8. Attempt to rotate the left rear wheel 1 full revolution clockwise and counterclockwise by hand. 

z

If the wheel does not rotate 1 full revolution in either direction, the locking differential is engaging 
properly.  

z

If the wheel rotates more than 1 revolution in either direction, the locking differential is not 
engaging properly.  

9. Disengage the differential lock switch.  

10. Attempt to rotate the left rear wheel 1 full revolution clockwise and counterclockwise by hand. 

z

If the wheel rotates 1 full revolution in either direction, the locking differential is disengaging 
properly.  

z

If the wheel does not rotate more than 1 revolution in either direction, the locking differential is not 
disengaging properly.  

11. If the locking differential is not functioning properly, remove the differential and determine the cause of 

failure. Refer to Differential Replacement in Rear Drive Axle and Locking Differential Disassemble .  

ELECTRONIC REAR DIFFERENTIAL LOCK WILL NOT ENGAGE 

Circuit Description 

The rear differential control circuit consists of a actuator (coil) 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: 

z

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

z

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. 

2: This step determines if the fault is present or intermittent.  

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

 

2004 Hummer H2 

2004 DRIVELINE/AXLE Drive Axle - Locking/Limited Slip - Hummer H2

  

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

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

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

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

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

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

10: This step refers to transfer case shift control module replacement.  

11: This step refers to encoder motor replacement.  

12: This advises to replace the transfer case shift control switch.  

Electronic Rear Differential Lock Will Not Engage 

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 
- Transfer Case?

-

Go to Step 2

Go to Diagnostic 

System Check - 

Transfer Case in 

Transfer Case - 

BW4484

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 in 

Wiring Systems

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 

ohm

Go to Step 5

Go to Step 12

Check the 5-volt reference and switch signal 
circuits for an open, short, or high resistance 
between the transfer case shift control switch, 

 

2004 Hummer H2 

2004 DRIVELINE/AXLE Drive Axle - Locking/Limited Slip - Hummer H2