GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 Sonoma Pickup - 4WD 🢒 Body and Accessories 🢒 Stationary Windows 🢒 Defogger System Check

Step

Action

Normal Result(s)

Abnormal Result(s)*

1
  1. Turn the ignition switch to the ON position.
  2. Depress the defogger switch once.
    • The ON indicator lamp lights.
    • The heated mirrors (if equipped) and the rear defogger grid become warm to the touch within 2 minutes.
    • The defoggers turn OFF after 10 minutes.

2

Depress the defogger switch again.
    • The ON indicator lights.
    • The defoggers turn OFF after 5 minutes.

3
  1. Depress the defogger switch.
  2. Immediately depress the defogger switch again.
    • The indicator lamp turns OFF.
    • The defoggers turn OFF.

4

Manual HVAC Controller

Turn the dash lamps ON.

The defoggers switch illumination lamps turn ON.

Defogger Indicator Inoperative

5

Electronic HVAC Controller

  1. Inspect the function of the ECC control lead.
  2. Operate the blower mode switch and the temperature controls.

The blower mode switch and the temperature controls function as designed.

HVAC System Check in HVAC Systems with A/C - Automatic

* Refer to the appropriate symptom diagnostic table for the applicable abnormal result.