Bosch 16421 Oxygen Sensor - Downstream, Downstream Left or Downstream Right

Bosch Actual OE Oxygen Sensor for BMW and Rolls-Royce

Bosch Part Number 16421 is a narrow-band heated oxygen sensor built for downstream applications on select BMW and Rolls-Royce vehicles. It uses a threaded, specific-fit design with a 4-wire harness and round female connector to deliver accurate air-fuel-ratio feedback to the ECU.

As part of Bosch’s Actual OE Oxygen Sensor line, this sensor reflects Bosch’s long OE development history in oxygen sensing technology. The design uses advanced ceramic elements, controlled heater operation, and high-temperature-resistant materials for stable closed-loop operation across demanding exhaust conditions.

Key Features

• Part Number 16421
• Actual OE Oxygen Sensor line from Bosch
• Narrow-band heated oxygen sensor
• Specific fit with threaded mounting
• 4-wire harness with round female connector
• 22 mm hex size and 18 mm thread diameter
• Steel-finish metal housing
• Wiring harness included

Detailed Description

Bosch 16421 is an OE-style downstream oxygen sensor for BMW X6, BMW M3, BMW X5, BMW 550i, BMW 650i, BMW 750i, BMW 750Li, BMW 760Li, and Rolls-Royce Phantom applications listed below. It measures exhaust oxygen content so the engine control unit can maintain precise fuel control, stable combustion, and emissions performance. This Bosch oxygen sensor is a direct replacement choice for vehicles requiring a narrow-band heated sensor with the same connector style and mounting configuration.

This part cross-references BMW 11787539125 for the same application.

What This Sensor Helps Address

• Check engine light related to oxygen sensor performance
• Incorrect air-fuel ratio readings from the downstream sensor
• Slow closed-loop response after sensor aging
• Emissions test failures tied to sensor output issues
• Rough combustion control caused by degraded exhaust feedback

Fitment

• Fits 2010-2014 BMW X6, downstream.
• Fits 2008-2013 BMW M3, downstream.
• Fits 2010-2013 BMW X5, downstream.
• Fits 2007-2011 Rolls-Royce Phantom, downstream.
• Fits 2006-2010 BMW 550i, downstream left.
• Fits 2006-2010 BMW 650i, downstream left.
• Fits 2007-2010 BMW X5, downstream right.
• Fits 2006-2008 BMW 750i, downstream left.
• Fits 2006-2008 BMW 750Li, downstream left.
• Fits 2007-2008 BMW 760Li, downstream right.

Installation Notes and Tips

Confirm the connector shape, wire count, and mounting location before installation. Use the 18 mm thread size and 22 mm hex specification to match the correct oxygen sensor socket, and inspect the exhaust bung threads for damage or corrosion before threading in the new sensor. Verify downstream left or downstream right placement against the removed part to maintain correct sensor location on BMW X5, BMW 550i, BMW 650i, BMW 750i, BMW 750Li, BMW 760Li, BMW M3, BMW X6, and Rolls-Royce Phantom applications.

Quality Assurance

Bosch backs this oxygen sensor with more than five decades of OE development experience. The Actual OE Oxygen Sensor line is built to OE-proven standards for accuracy, durability, and consistent operation under heat and vibration.