Normal Operation

When the Mode Select Switch (MSS) is engaged into either 4H or 4L mode to lock the rear differential, a Pulse Width Modulated (PWM) signal is sent to the Electronic Locking Differential (ELD) field coil by the Transfer Case Control Module (TCCM) through the differential lock control circuit. This signal is a PWM signal which is initially 98% duty cycle to lock the differential and decreases to 40% duty cycle once the differential is locked. If the differential does not lock, the TCCM continues to send the signal for a set amount of time. If after a set period time the differential does not lock, the TCCM sets this code indicating low TCCM system voltage.

• DTC P187A:00 Transfer Case Control Module System Voltage Low - Rear Locking Differential Disabled: No Sub Type Information - The TCCM senses the system voltage below 11.5 volts at the differential lock control circuit. The ELD is disabled until locker switch is disengaged and re-engaged or for the remainder of the ignition cycle

This pinpoint test is intended to diagnose the following:

• Wiring, terminals or connectors
• TCCM