Bosch 18175 Oxygen Sensor - Downstream

Bosch Validated Oxygen Sensor for Subaru WRX and Forester

Bosch Part Number 18175 is a specific-fit, narrow-band heated oxygen sensor for downstream applications on select Subaru models. It provides the ECU with accurate air-fuel-ratio feedback to support stable combustion control and lower emissions.

Built on Bosch Validated Oxygen Sensor engineering, this replacement follows Bosch’s OE development history and uses a threaded metal housing, 4-wire blade-terminal design, and integrated wiring harness for a direct-fit service part.

Key Features

• Specific-fit downstream oxygen sensor for select Subaru applications
• Narrow-band heated sensor design for closed-loop fuel control
• 4-wire configuration with oblong female connector and blade terminals
• Threaded 18 mm mounting with 22 mm hex size
• Metal housing built for high-temperature and vibration exposure
• Wiring harness included for a cleaner replacement installation
• Bosch Part Number 18175 for catalog and cross-reference use

Product Details

Bosch Validated Oxygen Sensor 18175 is engineered as a standard replacement for downstream monitoring on 2015 Subaru WRX, 2020-2021 Subaru WRX, and 2014-2015 Subaru Forester. As a narrow-band heated O2 sensor, it helps the engine control unit read exhaust oxygen content and adjust fueling during closed-loop operation. Bosch’s oxygen sensor line is rooted in decades of OE development, including early thimble-style sensors and later planar narrowband designs that improved light-off speed and lambda accuracy. This part cross-references 22690AB010 for the same application.

What It Helps Address

• Check engine light related to downstream oxygen sensor faults
• Incorrect air-fuel ratio readings sent to the ECU
• Slow closed-loop response after sensor aging or contamination
• Emissions test failures tied to oxygen sensor performance
• Rough combustion control caused by inaccurate exhaust feedback

Installation Notes and Tips

Install this sensor in the downstream position only where listed. Verify the 18 mm thread size, 4-wire connector layout, and oblong female plug before installation. Because the sensor is threaded into the exhaust stream, allow the exhaust to cool fully before removal and use the correct oxygen sensor socket or 22 mm wrench size for service.

Compatible With 2015 Subaru WRX, downstream; 2020-2021 Subaru WRX, downstream; and 2014-2015 Subaru Forester, downstream. Bosch Part Number 18175 should be matched to the vehicle’s connector and position before replacement.

Quality Assurance

Bosch backs this oxygen sensor with more than five decades of OE sensor development and aftermarket supply experience. The Validated Oxygen Sensor line is built to deliver OE-proven fit, electrical connection, and exhaust feedback performance for the listed Subaru applications.