Bosch 15265 Oxygen Sensor - Downstream or Upstream

Bosch Oxygen Sensor for Mazda Applications

Bosch Engineered Oxygen Sensor 15265 is a narrow-band heated O2 sensor built for precise air-fuel-ratio feedback to the ECU. It supports stable combustion control and emissions management in select Mazda applications, including Mazda Protege and Mazda 626 fitments.

• Specific-fit oxygen sensor for confirmed Mazda applications
• Narrow-band heated sensor design for closed-loop fuel control
• 4-wire configuration with rectangular male connector and female terminals
• Threaded mounting with 18 mm thread size and 22 mm hex size
• Wiring harness included with 14.8 in harness length
• Metal housing and high-temperature-resistant construction for demanding exhaust conditions

Bosch Engineered Oxygen Sensor Line

The Bosch Engineered Oxygen Sensor line builds on Bosch OE development that began with early oxygen sensor designs and later advanced to planar narrowband technology. This product line focuses on faster sensor response, accurate lambda measurement, and reliable heater control for consistent closed-loop operation across changing engine loads.

Detailed Product Overview

Bosch 15265 uses a switching-type narrow-band design to report exhaust oxygen content to the engine control unit. That signal helps the ECU adjust fuel delivery during normal driving, cold starts, and warm operating conditions. The heated sensor design improves light-off behavior and supports quicker transition into closed-loop operation. This part cross-references Monroe Shocks & Struts (e.g., 172286) for the same application.

Vehicle Fitment

• Fits 2001-2003 Mazda Protege, Upstream. Alternative Fit 1; Bosch Engineered Oxygen Sensor.
• Fits 1999-2000 Mazda Protege, Upstream. Alternative Fit 1; with California Emission System; Bosch Engineered Oxygen Sensor.
• Fits 2001-2002 Mazda 626, Downstream. Bosch Engineered Oxygen Sensor.
• Fits 2000 Mazda 626, Downstream. with California Emission System; Bosch Engineered Oxygen Sensor.

What This Sensor Helps Address

• Faulty oxygen sensor readings that trigger check engine lights
• Unstable air-fuel mixture control during closed-loop operation
• Reduced fuel economy caused by inaccurate exhaust feedback
• Emissions test failures related to sensor response or signal quality
• Slow sensor warm-up after startup

Installation Notes and Tips

Verify the connector shape, wire count, thread diameter, and sensor position before installation. This Bosch 15265 is a specific-fit, threaded oxygen sensor with a 4-wire harness and a 18 mm thread size, so matching the original connector and mounting location is important for proper installation. Confirm whether your Mazda application uses the upstream or downstream location listed in the fitment data.

Quality Assurance

Bosch backs this oxygen sensor with more than five decades of OE development in emissions and engine management sensing. The design uses ceramic sensing elements, controlled heater operation, and heat-resistant materials to support consistent performance in harsh exhaust environments.