Heat Wire Inspection

CAUTION: Use a dry and soft cloth when wiping dirt off the glass. Move the cloth along the heat wire to avoid damaging it.

Turn the ignition switch to ON.
Turn the defogger switch to ON.
Wrap the tips of tester probe with aluminum foil to avoid damage to heat wire.

Fig 1: Wrapping Tips Of Tester Probe With Aluminum Foil
Courtesy of SUBARU OF AMERICA, INC.

Measure the voltage at heat wire center with DC voltmeter.

Standard voltage: Approx. 6 V

Fig 2: Measuring Voltage At Heat Wire Center With DC Voltmeter

Courtesy of SUBARU OF AMERICA, INC.

RESISTANCE SPECIFICATION CHART

Voltage	Criteria
Approx. 6 V	Normal operation
Approx. 12 V or 0 V	Open

NOTE:

If the measured value is 12 volts, heat wire is open between heat wire center and positive (+) terminal of tester probe.
If it is 0 V, the circuit is open between heat wire center and ground.

Connect the tester probe of positive lead of voltmeter to positive terminal of heat wire and move tester probe of negative lead along the heat wire up to the negative terminal end. If voltage changes from zero to several volts during movement of tester probe, heat wire is open at the voltage change point.