Bosch 13721 Oxygen Sensor - Upstream

Bosch OE Oxygen Sensor for Porsche 911

Bosch 13721 is a narrow-band heated oxygen sensor built for precise air-fuel-ratio feedback to the ECU. It is a specific-fit, threaded upstream sensor for 1995-1998 Porsche 911 applications, including Porsche 911 oxygen sensor replacement needs where stable closed-loop control and emissions performance matter.

Key Features

• Actual OE Oxygen Sensor from Bosch
• Narrow-band heated design for faster closed-loop operation
• Specific fit with threaded mounting
• 4-wire harness with blade terminals and oblong connector
• 30.6 in wiring harness length and 34.3 in overall length
• 18 mm thread diameter and 22 mm hex size
• Metal housing with high-temperature-resistant construction
• Fits 1995-1998 Porsche 911, upstream

Product Details

Bosch 13721 uses a switching-type oxygen sensing element to report exhaust oxygen content to the engine control unit, helping maintain accurate fuel control across changing operating conditions. Bosch developed this sensor line from its original OE oxygen sensor technology and later planar narrowband designs, focusing on quicker light-off, improved lambda accuracy, and stable operation under heat and vibration. For Porsche 911 upstream sensor service, Bosch 13721 provides an OE-style replacement built around the same type of engineering used by vehicle manufacturers. This part cross-references 99360611601 for the same application.

Common Issues This Sensor Can Address

• Check engine light related to oxygen sensor performance
• Rich or lean fuel mixture readings at the ECU
• Slow closed-loop response after startup
• Emissions test failures tied to sensor degradation
• Rough idle or unstable combustion control from inaccurate exhaust feedback

Installation Notes and Tips

Confirm the upstream location before ordering, since this Bosch 13721 application is specific to the Porsche 911 position listed. Verify the 18 mm thread size, 22 mm hex, 4-wire connector layout, and harness length against the original sensor before installation. Inspect the connector routing and exhaust-side clearance so the harness is not strained or exposed to excessive heat.

Quality Assurance

Bosch has more than five decades of OE oxygen sensor development and supplies aftermarket sensors built to OE-proven standards. Bosch 13721 is engineered with ceramic sensing elements, controlled heater operation, and heat-resistant materials for consistent performance in demanding exhaust environments.