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 4 LO 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.
This DTC detects a short to ground, short-to-voltage, or an open circuit.
Conditions for Running the DTC
| • | The ignition is ON. |
| • | The system voltage is 9-18 volts. |
Conditions for Setting the DTC
| • | The transfer case shift control module monitors the state of the rear axle differential lock actuator. The transfer case shift control module reads the rear differential lock control, and the rear differential lock return circuits for a high and low voltage. The DTC will set if these circuits are high when a low voltage is expected or when the circuits are low when a high voltage is expected. |
| • | The DTC will set if this circuit is high when a low voltage is present or when the circuit is low when a high voltage is present. |
Action Taken When the DTC Sets
| • | All rear differential lock requests will be disabled. Transfer case mode shifts will not be affected. |
| • | SERVICE 4WD indicator will be latched on for the remainder of the current ignition cycle. |
Conditions for Clearing the DTC
| • | The Transfer case shift control module will clear the DTC if the condition for setting the DTC is not currently present. |
| • | A history DTC will clear after 33 consecutive ignition cycles without a fault present. |
| • | History DTCs can be cleared using a scan tool. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step determines of the coil has excessive resistance or if the windings are shorted together.
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This step determines if the coil or pigtail is shorted to ground.
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This step determines if either the differential lock control or differential lock return circuits are shorted to ground.
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This step determines if the differential lock control and differential lock return circuits are shorted together.
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This step tests for an open or high resistance in both the return and control circuits.
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This step has the system reconnected and retested to see if the DTC resets.
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This step refers to transfer case shift control module replacement.
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This step refers to rear differential lock coil replacement.
Step | Action | Value (s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Transfer Case Control Schematics in Transfer Case - BW 4493/4494 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 in Vehicle DTC Information | |
Was the resistance reading within the specified values? | 2.2-4.3 ohms | Go to Step 3 | Go to Step 9 | |
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 9 | Go to Step 4 | |
Was the condition found and corrected? | -- | Go to Step 10 | Go to Step 5 | |
|
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. 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? | -- | Go to Step 10 | Go to Step 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 10 | Go to Step 7 | |
Connect connectors C1 and C2 at the transfer case shift control module. Then connect the connector at the rear differential coil pigtail and retest the system. Does the DTC reset? | -- | Go to Step 8 | System OK | |
Replace the transfer case shift control module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Was the repair completed? | -- | Go to Step 10 | -- | |
Replace the rear differential lock coil. Refer to Electronic Locking Differential Coil Lock Replacement . Was the repair completed? | -- | Go to Step 10 | -- | |
10 |
Does the DTC reset? | -- | Go to Step 1 | System OK |
