Circuit Description
The front axle control circuit consists of a Front Drive Axle Clutch solenoid which is electronically controlled by the transfer case shift control module. This solenoid opens and closes a vacuum control valve allowing vacuum to apply and release a clutch pack inside the front axle housing. The transfer case shift control module determines whether or not the clutch pack is applied or released based on a signal from the front axle switch mounted on the front axle housing assembly. The front axle is normally locked or engaged during AUTO 4WD, 4WD HI, and 4WD LO modes. The front axle is unlocked or disengaged only during 2 HI or neutral modes.
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
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Helps determine whether the transfer case shift control module has electronic control of the front axle actuator.
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Tests the operation of the front axle switch by determining whether the state of the front axle switch is correct.
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Determines whether correct vacuum is supplied to the front axle actuator.
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Tests for proper voltage supplied to the front axle solenoid.
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Helps determine continuity through the front axle control circuit (testing the wiring and module driver).
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Tests the front axle circuit for an open.
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Tests the front axle switch for an internal open.
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Tests the front axle switch feed circuit for proper voltage.
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Tests the front axle switch circuit for an open.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Transfer Case Diagnostic System Check performed? | -- | Go to Step 2 | Go to Diagnostic System Check |
Does the Front Axle Switch status change with each command? | -- | Go to Step 11 | Go to Step 3 | |
Drive the vehicle in four wheel drive mode in order to determine if torque is being applied to the front wheels (the vehicle will display crow-hop or jerking during tight turns). Is torque being applied to the front wheels? | -- | Go to Step 8 | Go to Step 4 | |
While the engine is running, inspect the front drive axle clutch solenoid for proper vacuum supply. Is there proper vacuum supplied to the front drive axle clutch solenoid? | -- | Go to Step 5 | Go to Step 12 | |
5 |
Is the voltage reading within the value specified? | B+ | Go to Step 6 | Go to Step 13 |
6 |
Is the resistance reading within the specified values? | 0-2 ohms | Go to Step 15 | Go to Step 7 |
7 | Test the front axle control circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Was the condition found and corrected? | -- | Go to Step 17 | Go to Step 16 |
8 |
Does the Front Axle Switch status change from Unlocked to Locked? | -- | Go to Step 14 | Go to Step 9 |
9 |
Is the voltage reading within the value specified? | B+ | Go to Step 10 | Go to Step 11 |
10 |
Was the condition found and corrected? | -- | Go to Step 17 | Go to Step 16 |
11 | Repair an open or short to ground in the front axle switch feed circuit. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 17 | -- |
12 | Repair a vacuum leak between the engine and the front drive axle clutch solenoid. Is the repair complete? | -- | Go to Step 17 | -- |
13 | Repair the front drive axle clutch solenoid feed for an open or short to ground. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 17 | -- |
14 | Replace the front axle switch. Did you complete the replacement? | -- | Go to Step 17 | -- |
15 | Replace the front axle actuator. Refer to Vacuum Actuator Replacement in Front Axle. Did you complete the replacement? | -- | Go to Step 17 | -- |
16 | Replace the transfer case shift control module. Refer to Transfer Case Shift Control Module Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- |
17 |
Does the symptom re-occur? | -- | Go to Step 2 | System OK |
