C0387

DTC C0387









Circuit Description
The Transfer Case Motor is a bi-directional, permanent magnet, D.C. motor. When energized, (through Motor Control A or Motor Control B. the ground is provided by the opposing Motor Control circuit and then grounded through the transfer case shift control module ground circuit), the motor, through a series of gears, rotates a shaft which moves the mode and range forks to shift the Transfer Case between 4H, AUTO 4WD, 2H, N. and 4L ranges.
This DTC detects that the transfer case is unable to successfully complete a shift to a requested mode or range.

Conditions for Setting the DTC
^ The transfer case shift control module will test the motor circuits and determine that there are no motor circuit faults existing.
^ The transfer case shift control module has attempted to shift to a requested mode/range and has failed to reach the desired position.
^ The transfer case shift control module has performed a default shift to 4LO or 4HI.

Action Taken When the DTC Sets
^ The SERVICE indicator (AWD/4WD) lamp will be latched on for the remainder of the current ignition cycle.
^ All shifting will be disabled.
^ The range/mode lights will be disabled
^ The next ignition cycle, the transfer case shift control module will power-up as if the 4HI was the mode present when the ATC was powered down.

Conditions for Clearing the DTC
^ The transfer case shift control module will clear the DTC if the condition for setting the DTC no longer exists.
^ A history DTC will clear after 100 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.
2. Tests whether the transfer case shift control module is sensing any change in all of the encoder channels.
3. Helps determine whether the shift is prevented due to a mechanical fault.
4. Tests whether the transfer case shift control module is sensing any change in any of the encoder channels.
5. Tests if proper reference voltage is being supplied to the encoder from the suspect circuit.
6. Helps determine whether a short between 2 or more encoder circuits exist.
7. Tests the suspect encoder circuit for the module's ability to sense the circuit going low.
8. Helps determine whether the shift is prevented due to a mechanical fault.
9. Tests for the electrical energizing of the encoder motor.
10. Tests the suspect circuit(s) for an open or a short to power.
11. Tests for short between the suspect circuits.