Ford 2003 Mustang Workshop Manual page 3744

Is the voltage greater than 10 volts?
I4 CHECK THE ICM FOR CORRECT OPERATION
Disconnect all ICM connectors.
Check for:
corrosion
pushed-out pins
Connect all ICM connectors and make sure they seat
correctly.
Operate the system and verify the concern is still
present.
Is the concern still present?
Component Tests
Grid Wire Test
1. Using a bright lamp inside the vehicle, inspect the wire grid from the exterior. A broken grid wire
will appear as a brown spot.
2. Run the engine at idle. Set the rear window defrost switch to ON. The indicator light should
come on.
3. Working from the interior of the vehicle with a voltmeter, contact the broad red-brown stripes of
the rear glass window positive lead to battery side and negative lead to ground side. The meter
should read 10-13 volts. A lower voltage reading indicates a loose ground connection.
4. Contact a good ground point with the negative lead of the meter. The voltage reading should not
differ.
5. With the negative lead of the meter grounded, touch each grid line of the heated rear window
glass at its midpoint with the positive lead. A reading of approximately 6 volts indicates that the
line is good. A reading of zero volts indicates that the line is broken between the midpoint and
the B+ side of the grid line. A reading of 12 volts indicates that the circuit is broken between the
midpoint of the grid line and ground.
Yes
INSTALL a new ICM. REFER
to Section 413-01 . CLEAR the
DTCs. REPEAT the self-test.
No
The system is operating
correctly at this time. Concern
may have been caused by a
loose or corroded connector.
CLEAR the DTCs. REPEAT
the self-test.