The defogger on your Oldsmobile Alero helps to keep the rear window clear of water vapor during the cold weather months by flowing current through the grid. The wiring is mounted on the inner side of the window. However, the timer relay, switch, fuse, grid and wires in the circuit connecting these components are subject to wear and damage. Finding the failed component can be a little tricky, but with some basic strategies--and tracing the current flow in the circuit--you can troubleshoot and fix your Alero rear defogger.
Check the window defogger fuse. If it is blown, replace it and operate the defogger to make sure it is working now.
Open the driver’s door, turn the ignition switch to the "on" position and, as you look at the interior dome light at the ceiling of your vehicle, turn on the defogger switch. If the light stays bright, proceed to Step 3. If the light seems to go almost off, go directly to Step 5.
Start the engine and turn on the defogger switch. Check for incoming voltage on both sides of the connection at the grid of the rear window using a test light. Repair the connection if necessary. If you detect incoming voltage at the connection as you operate the switch, make sure there is current flowing for about 10 minutes. Otherwise, the timer relay is defective and you need to replace it. Turn off the engine.
Trace the circuit for continuity between the fuse, the timer relay, the switch and the connector on the rear window using the test light. Repair any opens or shorts on the circuit, or replace the relay or switch as necessary.
Check the defogger closely for missing or broken wires along the grid. Start the engine and turn the defogger switch on.
Allow the grid to warm up for two or three minutes. Then touch the grid close to the positive side of the connection. The grid should feel warm. Follow the grid with your hand. Locate the spot where the grid feels colder and locate the broken wire on the grid around that spot. If necessary, use your test light to locate the open on the grid. When the test light stops glowing, you have found the broken part of the wire. Repair the grid using a rear window defogger repair kit.
