Bosch 17404 Oxygen Sensor - Upstream

Bosch Wideband OE Oxygen Sensor

Bosch 17404 is an Actual OE Oxygen Sensor built for precise air-fuel ratio measurement in wideband applications. It uses a heated, 5-wire design with a specific-fit harness to deliver accurate upstream feedback for BMW engine management systems.

For BMW M240i, X3, X4, 440i, 540i, 740i, and related models, this Bosch wideband A/F sensor provides the detailed signal the ECU needs for stable mixture control across changing load and temperature conditions. Part number 17404 is a direct replacement choice for drivers restoring factory-style emissions and drivability performance.

Key Features

• Wideband oxygen sensor for continuous air-fuel ratio measurement
• Heated design for faster light-off and improved cold-start response
• Specific-fit application with included wiring harness
• 5-wire configuration with blade terminals and oblong connector
• Threaded mounting with 18 mm thread diameter and 22 mm hex size
• Metal housing with robust ceramic sensor construction
• Upstream location for OE-style engine management feedback

Product Details

Bosch pioneered the wideband A/F oxygen sensor design, and this Actual OE Oxygen Sensor reflects that OE development history. Unlike traditional switching sensors, a wideband sensor measures across the full lambda range, giving the ECU more precise information for fuel control, performance consistency, and emissions management. Bosch 17404 is engineered as a standard replacement for specific BMW applications and is listed as an upstream sensor for multiple 2016-2021 BMW models.

This part cross-references Bosch 17404 for the same application.

What It Helps Address

• Check engine light related to upstream oxygen sensor faults
• Incorrect air-fuel ratio readings
• Rough idle or inconsistent throttle response caused by sensor degradation
• Reduced fuel economy from inaccurate mixture control
• Emissions test failures tied to oxygen sensor performance

Installation Notes and Tips

Compatible With 2016-2021 BMW applications listed below as an upstream sensor. Confirm connector shape, wire count, thread size, and sensor position before installation. Use proper oxygen sensor service tools to avoid damaging the 18 mm threaded bung or the sensor body. Verify the harness routing keeps the lead clear of exhaust heat and moving components.

• Fits 2017-2021 BMW M240i, Upstream
• Fits 2017-2021 BMW M240i xDrive, Upstream
• Fits 2018-2021 BMW X3, Upstream
• Fits 2019-2021 BMW X4, Upstream
• Fits 2017-2020 BMW 440i, Upstream
• Fits 2017-2020 BMW 440i Gran Coupe, Upstream
• Fits 2017-2020 BMW 440i xDrive, Upstream
• Fits 2017-2020 BMW 440i xDrive Gran Coupe, Upstream
• Fits 2017-2020 BMW 540i, Upstream
• Fits 2017-2020 BMW 540i xDrive, Upstream
• Fits 2016-2020 BMW 740i, Upstream
• Fits 2017-2020 BMW 740i xDrive, Upstream
• Fits 2017-2019 BMW 340i GT xDrive, Upstream
• Fits 2018-2019 BMW 640i xDrive Gran Turismo, Upstream
• Fits 2016-2018 BMW 340i, Upstream
• Fits 2016-2018 BMW 340i xDrive, Upstream

Quality Assurance

Bosch supplies OE-level oxygen sensor technology backed by more than five decades of engine management development. Part number 17404 is built to OE specifications for accurate signal response and dependable operation in modern wideband applications.