Bosch 13866 Oxygen Sensor - Downstream

Bosch Validated Oxygen Sensor for Mazda Miata

Bosch Validated Oxygen Sensor 13866 is a narrow-band heated O2 sensor built for precise air-fuel-ratio feedback to the ECU. It is a specific-fit replacement for 2001-2005 Mazda Miata downstream applications, with the harness and connector configuration needed for a direct service replacement.

Key Features

• Specific-fit oxygen sensor for downstream placement
• Narrow-band heated sensor design for closed-loop fuel control
• 4-wire configuration with rectangular male connector
• Threaded mounting with 18 mm thread diameter and 22 mm hex size
• Wiring harness included with 37.4 in harness length and 41.1 in overall length
• Standard replacement grade for emission control service
• Bosch Validated Oxygen Sensor line backed by Bosch OE development experience

Product Details

Built under the Bosch Validated Oxygen Sensor line, part number 13866 reflects Bosch’s long history in oxygen sensor development, including early thimble-style designs and later planar narrowband technology. This sensor uses advanced ceramic elements, controlled heating, and high-temperature-resistant materials to maintain stable signal output under heat and vibration. For Mazda Miata owners servicing the downstream sensor circuit, Bosch 13866 provides the air-fuel feedback needed for accurate combustion control and emissions monitoring.

This part cross-references Mazda OE numbers BP6G18861C9U and BP8K188619U for the same application. Fits 2001-2005 Mazda Miata, downstream.

What It Helps Address

• Check engine light related to downstream oxygen sensor performance
• Incorrect air-fuel ratio readings reported to the ECU
• Slow closed-loop response after sensor aging or contamination
• Emissions test failures tied to oxygen sensor signal issues
• Rough combustion control caused by degraded narrow-band output

Installation Notes

Install as a threaded oxygen sensor in the downstream location on compatible Mazda Miata applications. Verify connector shape, wire count, and harness length against the original sensor before installation. Use the 22 mm hex size for removal and installation, and confirm the 18 mm thread size matches the exhaust bung.

Quality Assurance

Bosch draws on more than five decades of OE oxygen sensor development, and the Validated Oxygen Sensor line is built to OE-proven standards for accuracy, durability, and consistent signal control in demanding exhaust conditions.