my BMW 3 Series E90/E91’s rear defroster is not working, how can I fix it?

Solution

1. Preparation

• Gather tools and parts needed for repair.
• Ensure the vehicle is parked on a flat surface and the ignition is off.
• Disconnect the negative battery terminal to ensure safety.

2. Inspect and Replace the Fuse

• Tools Required: Fuse puller or pliers.
• Locate the fuse box. For the E90/E91, the fuse box is typically located on the driver's side under the dashboard.
• Identify the rear defroster fuse using the fuse diagram in the fuse box cover.
• Remove the fuse and inspect it for a break in the filament.
• If the fuse is blown, replace it with a new fuse of the same amperage (usually 30A).

3. Check the Defroster Relay

• Tools Required: Multimeter.
• Locate the defroster relay in the fuse box.
• Remove the relay and use the multimeter to check for continuity.
• If the relay is faulty, replace it with a new one.

4. Inspect the Rear Defroster Grid

• Tools Required: Visual inspection tools (magnifying glass).
• Inspect the defroster grid lines on the rear window for any breaks or damage.
• If broken lines are found, repair them using a rear window defroster repair kit.

5. Reassemble and Test the System

• Reconnect the negative battery terminal.
• Turn on the ignition and activate the rear defroster.
• Check if the rear defroster indicator light illuminates and test the defroster's operation.