501-11 Glass, Frames and Mechanisms 2014 Fiesta
Description and Operation Procedure revision date: 05/7/2013

Glass, Frames and Mechanisms - Vehicles With: Front Manual Windows - System Operation and Component Description

System Operation

System Diagram - Rear Window Defrost (with EATC )

Network Message Chart - Rear Window Defrost (with EATC )

  BCM Network Input Messages

Broadcast Message Originating Module Message Purpose
Defrost Mode HVAC - EATC When the rear window defrost button is pressed, this message is used by the BCM to supply voltage to the rear window defrost grid.

Rear Window Defrost

The engine must be running for the rear window defrost system to operate. When the rear window defrost switch (integral to the HVAC module) is pressed, a ground signal (if equipped with EMTC ) or message (if equipped with EATC ) is sent to the BCM . When the BCM receives the defrost request, it supplies voltage to the rear window defrost grid. The rear defrost self actuates when the ambient air temperature is less than 5° C (41° F) and engine coolant temperature is less than 60° C (140° F). The rear window defroster LED indicator does not illuminate when the rear defroster self actuates.

The BCM deactivates the rear window defrost grid when one of the following conditions is met:

Component Description

HVAC Module

The HVAC module contains the rear window defrost switch.


The BCM module controls the accessory relay which supplies voltage to operate the power window system. The BCM also supplies the high current voltage to operate the rear window defrost grid.