Bosch 15804 Oxygen Sensor - Upstream

Bosch Validated Oxygen Sensor for Ford Focus

Bosch Validated Oxygen Sensor 15804 is a specific-fit, narrow-band heated O2 sensor for select Ford Focus applications. It provides direct air-fuel-ratio feedback to the ECU for stable closed-loop control and emissions monitoring.

Key Features

• Specific-fit replacement for select 2003-2007 Ford Focus upstream applications
• Narrow-band heated oxygen sensor for faster closed-loop operation
• 4-wire design with blade terminals and rectangular connector
• Threaded mounting with 18 mm thread size and 22 mm hex size
• Wiring harness included with 15.9 in harness length
• Metal housing built for high-temperature and vibration exposure
• Bosch Validated Oxygen Sensor line reflects Bosch OE development experience

Detailed Description

Bosch part number 15804 is a standard replacement oxygen sensor engineered for upstream placement on select Ford Focus models. It uses a heated narrow-band design to deliver accurate switching signals to the engine control unit, helping maintain proper combustion control during warm-up and normal driving. For drivers searching for a Ford Focus upstream oxygen sensor, Bosch 15804 offers the OE-style fit and sensor architecture expected for emissions-related service.

The Bosch Validated Oxygen Sensor line builds on Bosch’s long history in oxygen-sensor development, including early thimble-style designs and later planar narrowband technology. That background shows up in the sensor’s ceramic element, heater control strategy, and durable construction for thermal and vibration resistance. If you need a Bosch 15804 replacement for a 2003-2006 Ford Focus upstream sensor located in the exhaust manifold, or a 2005-2007 Ford Focus upstream sensor, this part matches the listed application.

This part cross-references Bosch 15804 for the same application.

What It Helps Address

• Check engine light related to oxygen sensor performance
• Incorrect air-fuel ratio feedback to the ECU
• Slow closed-loop response after startup
• Emissions test failures tied to upstream sensor faults
• Rough combustion control caused by a worn narrow-band sensor

Installation Notes and Tips

Install this sensor in the upstream position only for the listed Ford Focus applications. Verify the 18 mm thread size, 22 mm hex size, 4-wire connector, and rectangular male connector before installation. Because the sensor is threaded and heated, inspect the exhaust manifold threads and wiring route carefully to avoid damage during removal and installation.

Quality Assurance

Bosch draws on more than five decades of OE oxygen-sensor development, and the Validated Oxygen Sensor line is built to the same OE-proven standards used by vehicle manufacturers. Bosch 15804 is engineered for consistent signal accuracy and durable service in demanding exhaust conditions.