Normal Operation
WARNING: This page is about a different car, the 2012 Ford Pickup, 2012 Ford F550 Super Duty, 2012 Ford F450 Super Duty, and 2012 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
When the Mode Select Switch (MSS) is engaged 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. When the differential is starting to lock, the graphic in the Instrument Panel Cluster (IPC) message center starts to blink. When the differential is fully locked, the graphic illuminates steady.
- DTC P189A:00 (Axle Disconnect Input Switch Circuit Low: No Sub Type Information) - When not in locking mode, the TCCM senses the resistance to ground on circuit CCF32 and if the differential is always engaged. This DTC only displays during the self-test function.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- MSS
- TCCM