Bosch C3821WS Cabin Air Filter

Bosch Cabin Filter for BMW HVAC Systems

Bosch C3821WS is a cabin air filter with activated carbon media for BMW applications that call for OE-standard cabin filtration. It is built to help reduce outside odors and airborne contaminants entering the passenger compartment through the HVAC system.

The Bosch Cabin Filter, Activated Carbon line adds a carbon layer for odor control and a protective cover layer for added filtration support. For BMW 525i, 530i, 540i, M5, and 528i applications, this filter is a direct replacement choice for maintaining cleaner cabin air and consistent HVAC performance.

Key Features

• Activated charcoal filter media for odor reduction
• 5-layer design with an additional carbon layer and cover layer
• OE standard part construction
• Foam automotive material
• Recommended replacement interval: 12,000 miles
• Previously cataloged as Bosch C3821

Detailed Product Overview

Bosch C3821WS is designed for BMW cabin air filtration where activated carbon is specified. The filter media uses charcoal to absorb common exhaust-related odors and gases, including ozone, nitrogen oxide, sulfur dioxide, and hydrocarbons. That makes it a practical service part for drivers looking to maintain a cleaner HVAC air path in daily use.

This Bosch Cabin Filter, Activated Carbon product line focuses on multi-layer filtration rather than basic dust capture alone. The added carbon layer and protective cover layer support cabin air quality in vehicles such as the BMW 525i, BMW 530i, BMW 540i, BMW M5, and BMW 528i. Part number C3821WS also cross-references BMW 64312207985 for the same application.

What This Cabin Filter Helps Address

• Unpleasant odors entering the cabin through the HVAC system
• Dust and airborne debris passing through the ventilation intake
• Reduced cabin air freshness during city or highway driving
• Service intervals where the existing cabin filter is overdue
• HVAC airflow issues caused by a restricted filter element

Installation Notes and Tips

Replace the cabin air filter at the recommended 12,000-mile interval or sooner if odor control or airflow has declined. Confirm the vehicle’s cabin filter location before service, and verify fitment by year, make, and model before installation. Compatible applications include Fits 2001-2003 BMW 525i, N/A; Fits 2001-2003 BMW 530i, N/A; Fits 1997-2003 BMW 540i, N/A; Fits 2000-2003 BMW M5, N/A; and Fits 1997-2000 BMW 528i, N/A.

Quality Assurance

Bosch manufactures this cabin filter as an OE-standard replacement part for BMW HVAC service. The activated carbon construction and multi-layer design reflect Bosch’s focus on filtration performance and consistent fitment for the listed applications.