RE: Service 4wd
There will usually be a code e.g. DTC C0327 encoder motor circuit fault. But you need tech2 to pull the codes.
The transfer case shift control module has 4encoder circuits, and each circuit is supplied 12volts. These 4circuits are A, B, C, and P, and each circuit runs to a switch located inside the encoder/motor assembly. When a particular encoder circuit is active, the switch is closed, and the 12volts are grounded by the switch inside the encoder.
The transfer case shift control module supplies 12volts on all the circuits. The module can interpret the location of the transfer case shift position when the circuits are grounded.
This DTC detects a fault when it compares the shift sequence/strategy to a chart located in read only memory (ROM), within the electronic control unit (ECU), within the transfer case shift control module. This is accomplished by the module reading the different combinations of encoder signals being grounded while others remain high depending on what mode or range the transfer case is in.
The transfer case shift control module sets the DTC when the encoder signals do not match the chart contained in ROM. This DTC can be set while no shift is requested or while a shift is being performed.