4WD Low Switch Signal Check

CIRCUIT DESCRIPTION
The 4WD low circuit consists of a transfer case switch, front axle actuator, and wiring. The PCM supplies a B+ voltage signal to the transfer case switch on CKT 1493. With 2WD or 4WD HI selected, no ground path is provided for CKT 1493, and the voltage signal at the PCM will be B+. When 4WD low is selected, the transfer case switch provides a ground for CKT 1493, and the PCM 4WD low signal CKT 1493 will change from B+ to zero volts. The transfer case switch also completes CKT 50 (B+) to CKT 1296 to provide B+ to the front axle actuator.

ACTION TAKEN (PCM WILL DEFAULT TO)
No DTC(s) will be set, however, failures of the 4WD low circuit can cause many types of complaints such as early/late shifts, erratic shifts.

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This test checks for proper circuit operation.
2. This test checks for a proper reference signal from the PCM.
3. This test checks the ability of the transfer case switch to ground the reference signal from the PCM.

DIAGNOSTIC AIDS
For further information, refer to Transfer Case.