With VCM-A

4WD Low Switch Check (With Electric Shift) Diagnostic Chart:

4WD Low Switch Check (With Electric Shift) Wiring Schematic:

CIRCUIT DESCRIPTION
The 4WD low circuit consists of a selector assembly, Transfer Case Control Module (TCCM), front axle switch and wiring. When the operator selects 4WD low, a momentary signal will be sent from the selector switch to the TCCM. If all conditions for 4WD low have been met, the TCCM will allow the electric motor in the transfer case to make the shift. When 4WD low is engaged, CKT 1694 voltage to the Vehicle Control Module (VCM-A) will change from B+ to zero. The 4WD low switch signal is used to correct the transmission output speed signal to the VCM-A, this signal is used to compensate for transfer case gear reduction. The VCM-A uses the transmission output speed signal to adjust shift points, line pressure and Torque Converter Clutch (TCC) scheduling.

ACTION TAKEN (VCM-A will default to)
No Diagnostic Trouble Code (DTC)(s) will be set, however, if CKT 1694 is shorted to B+, and the transfer case is in 4WD low position, the transmission will have late upshifts in 4WD low. If CKT 1694 is shorted to ground or open, the transmission will have an early shift pattern.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic charts
1. This test checks for system self test.
2. This test checks for proper circuit operation.
3. This test creates an open in the circuit to verify the signal to the VCM-A.
4. This test checks for a faulty TCCM.
5. This test checks for an open in the circuit or a faulty VCM-A.


DIAGNOSTIC AIDS
For further information, refer to Transfer Case Electronic Controls. For further information on the "Electric Shift Transfer Case" circuit wiring refer to Electronic Shift Transfer Case electrical diagram.