Bosch 18174 Oxygen Sensor - Upstream

Bosch Oxygen Sensor for Subaru WRX and Forester

Bosch Validated Oxygen Sensor 18174 is a direct-fit emission control sensor for specific Subaru applications. It provides air-fuel ratio feedback to the ECU for stable closed-loop operation, accurate fuel control, and lower exhaust emissions.

• Direct-fit, specific application sensor
• Heated oxygen sensor with optimized heater control
• Wide band oxygen sensor design with narrow-band sensor type listing
• 5-wire harness with square female connector
• Threaded mounting, 18 mm thread diameter, 22 mm hex size
• Wiring harness included for a cleaner replacement
• Steel finish with metal housing for high-temperature service

Bosch Validated Oxygen Sensor Line

The Bosch Validated Oxygen Sensor line builds on Bosch OE development dating back to the original oxygen sensor designs introduced in 1976. Bosch later refined planar narrowband technology for faster light-off, improved lambda measurement, and quicker closed-loop response. Bosch 18174 follows that OE-focused approach with ceramic sensing elements, controlled heating, and materials selected for thermal and vibration resistance.

This part cross-references Subaru 22641AA650 for the same application.

Fitment Details

• Fits 2020-2021 Subaru WRX, Upstream
• Fits 2015 Subaru WRX, Upstream
• Fits 2014-2015 Subaru Forester, Upstream

Common Symptoms This Sensor May Address

• Check engine light related to oxygen sensor performance
• Rough idle or unstable air-fuel control
• Reduced fuel economy from inaccurate exhaust feedback
• Delayed closed-loop operation after startup
• Emission test failure tied to sensor response issues

Installation Notes

Confirm upstream placement before installation and verify connector shape, wire count, and thread size against the original sensor. Use the 18 mm threaded mounting and 22 mm hex size to match the vehicle’s exhaust bung, and route the 9.1-inch harness away from heat sources and moving components. Because this is a specific-fit replacement, compare the connector and terminal layout to the removed part before final tightening.

Quality Assurance

Bosch backs this oxygen sensor with more than five decades of OE sensor development and aftermarket supply experience. The design uses durable materials and heater control strategies intended to maintain consistent signal quality under demanding thermal and vibration conditions.