The accessory switch circuit consists of 4 modes of operation. The transfer case shift control module supplies a 5-volt reference to the accessory switch. A switch signal low circuit completes the path back to the transfer case shift control module. The voltage on the switch signal low circuit will vary depending on which mode button is pressed by the vehicle operator. The transfer case shift control module continuously monitors the switch signal low circuit to determine whether the Neutral, 2HI, 4HI, or 4LO mode was selected.

A low battery condition or charging system that is faulty could contribute to the front axle to not engage. Refer to Battery Inspection/Test and Charging System Test .

Schematic Reference

Transfer Case Control Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Transfer Case Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition OFF, disconnect the accessory switch electrical connector.
2. Verify that a test lamp illuminates between B+ and terminal H of the accessory switch connector.

⇒	If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

3. Ignition ON, verify that a test lamp illuminates between terminals A and H of the accessory switch connector.

⇒	If the test lamp does not illuminate test the ignition 1 voltage circuit for a short to ground or an open/high resistance.

4. Ignition ON, measure for 4.8-5.2 volts at terminal M of the accessory switch connector.

⇒	If greater than the specified value, test for a short to B+ on the 5-volt reference circuit. If the circuit tests normal, replace the transfer case shift control module.

⇒	If less than the specified voltage, test for a short to ground or an open/high resistance on the 5-volt reference circuit. If the circuit tests normal, replace the transfer case shift control module.

5. Ignition OFF, disconnect connector C1 at the transfer case shift control module.
6. Ignition ON, connect a 3A jumper wire between terminals M and N at the accessory switch connector. Measure for 4.8-5.2 volts at C1 terminal 14 of the transfer case control module.

⇒	If greater then the specified value, test for a short to B+ on the switch signal low circuit. If the circuits test normal, replace the transfer case shift control module.

⇒	If less than the specified value, test for a short to ground or an open/high resistance on the switch signal low circuit. If the circuit test normal, replace the transfer case shift control module.

1. Disconnect the accessory switch electrical connector.
2. Connect a DMM between terminals M and N on the accessory switch. You should measure the following resistance values while pressing and holding each of the mode buttons:

•	4HI: 656.2-669.4 ohms

•	2HI: 1.50-1.53 K ohms

•	Neutral: 1.010-1.031 K ohms

•	4LO: 2.32-2.36 K ohms

•	Normal: 9.00-9.18 K ohms

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.