With Mechanical Shift

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION
The 4WD low circuit consists of a 4WD indicator assembly, a selector switch assembly, front axle switch and wiring. When the operator moves the transfer case select lever to 4WD low, the selector switch completes CKT 39 to CKT 150. When the circuit is complete the 4WD low indicator lamp will illuminate, CKT 1694 to the PCM will change from B+ to zero. The front axle switch will close and complete CKT 1695 to CKT 150. The front axle switch will modify antilock brakes and illuminate the front axle lamp. The front axle switch does not effect CKT 1694 signal input to the PCM because the switch is also closed in the 4WD high position. The 4WD low switch signal is used to correct the transmission output speed signal from the Vehicle Speed Signal (VSS) Buffer Module to the PCM to compensate for transfer case gear reduction.

ACTION TAKEN (PCM WILL DEFAULT TO)
No DTC(s) will be set, however, if CKT 1694 is shorted to B+, the transmission will have late or no 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 chart.
1. This test checks for mechanical adjustment and ignition feed.
2. This test checks for proper circuit operation.
3. This test creates an open in the circuit to verify the signal to the PCM.
4. This test checks for an open in the circuit to verify the signal to the PCM.
5. This test check for an open in the circuit or a faulty PCM.