Hummer H3. Manual — part 985

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 step replaces 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 - 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

1. With a DMM, check the

resistance of the transfer
case shift control switch.

2. While depressing and

holding the differential lock

2007 Hummer H3

2007 Driveline/Axle Rear Drive Axle - H3

4

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

1. Disconnect the C1 from the

transfer case shift control

2007 Hummer H3

2007 Driveline/Axle Rear Drive Axle - H3

8

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

-

Replace the transfer case shift

2007 Hummer H3

2007 Driveline/Axle Rear Drive Axle - H3

ELECTRONIC REAR DIFFERENTIAL LOCK WILL NOT DISENGAGE

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.

2: This step determines if the differential lock is engaged due to an electrical condition or a

12

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

2007 Hummer H3

2007 Driveline/Axle Rear Drive Axle - H3