Circuit Description
This symptom is usually the result of actions expected to take place during the transition of a transfer case mode change which has not happened. When the transfer case changes from 2WD to 4WD (for example), the front axle is Locked by the transfer case shift control module. If the transfer case shift control module does not sense that the front axle is applied, it waits for the action to take place before the gear change is made. While waiting, the mode switch lamp will continue to flash for a period of time, at which time all other mode requests will be ignored for the duration of the ignition cycle.
The front axle control circuit consists of an electric motor actuator which engages and disengages the front axle. The front axle actuator's motor consists of a Permanent Magnetic (PM) motor, a worm gear controlled plunger, a front axle switch and an electronic control circuit all within the actuator assembly.
The front axle actuator has four circuits connected to it, a front axle feed circuit, front axle ground circuit, front axle control circuit and a front axle switch circuit.
Whenever a shift to AUTO 4WD, 4HI, or 4LO is requested, the transfer case shift control module engages the front axle by grounding the front axle control circuit through a current limiting driver.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Determine the position of the Front Axle Switch.
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Helps determine if the front axle will not engage.
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Helps determine if the front axle will not disengage.
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 scan tool display the Front Axle Switch status as Locked? | -- | Go to Step 4 | Go to Step 3 | |
Use the scan tool in order to read the Commanded Mode Indicator status. Is the transfer case in Auto 4WD, 4WD HI, 4WD Low mode? | -- | Go to Step 5 | ||
Use the scan tool in order to read the Encoder Gear Position status. Is the transfer case in 2WD mode? | -- | Go to Step 5 | ||
5 | Replace the transfer case shift control module. Refer to the Transfer Case Shift Control Module Replacement . Is the repair complete? | -- | Go to Step 6 | -- |
6 |
Does the symptom re-occur? | -- | Go to Step 2 | System OK |
