C0387

DTC C0387

Circuit Description
The transfer case encoder is a switch that converts a shaft position, representing a mode or range position, into electrical signals for use by the transfer case shift control module. The encoder houses 4 hall effect sensors that are used for channels P, A, B, and C. These sensors provide a path to ground when a magnet, part of the motor encoder, passes over them.

The transfer case shift control module supplies an 8-volt reference and a ground circuit for the encoder hall effect sensors to function.

The transfer case shift control module supplies current limited 5 volts on all the channels. As these channels are pulled to ground, the module can interpret the location of the transfer case shift position.

This DTC detects that the transfer case is unable to successfully complete a shift to a requested mode or range.

DTC Descriptor
This diagnostic procedure supports this DTC:
DTC C0387 Unable to Perform Shift

Conditions for Running the DTC
^ The ignition is ON.
^ The system voltage is 9-16 volts.

Conditions for Setting the DTC
^ The transfer case shift control module tests the motor circuits and determines 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 4WD indicator remains illuminated for the remainder of the current ignition cycle.
^ All shifting is disabled.
^ The range/mode lights are 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 clears the DTC if the condition for setting the DTC no longer exists.
^ A history DTC clears after 100 consecutive ignition cycles without a fault present.
^ History DTCs can be cleared using a scan tool.

Steps 1-11:

Steps 12-15:

Test Description
These numbers correspond to the step numbers on the diagnostic table.
3. This step tests whether the transfer case shift control module is sensing any change in all of the encoder channels.
4. This step helps determine whether the shift is prevented due to a mechanical fault.
5. This step tests whether the transfer case shift control module is sensing any change in any of the encoder channels.
6. This step tests if proper reference voltage is being supplied to the encoder from the suspect circuit.
7. This step helps determine whether a short between 2 or more encoder circuits exist.
8. This step helps determine whether the shift is prevented due to a mechanical fault.
9. This step tests for the electrical energizing of the encoder motor.
10. This step tests the suspect circuits for an open or a short to power.
11. This step tests for a short between the suspect circuits.