Denso 234-4390 Oxygen Sensor - Downstream

Denso 234-4390 Oxygen Sensor Overview

Denso 234-4390 is a specific-fit heated oxygen sensor built to OE-style requirements for direct replacement in the exhaust stream. It is engineered for downstream use on select Mazda applications, including the Mazda 3 and Mazda 5, with a 4-wire female connector and threaded mounting for a precise match.

Denso’s OE Style line focuses on exact replacement fitment and consistent sensor response. This oxygen sensor uses an aluminum oxide trap layer to help protect the ceramic element from silicone and lead contamination, supporting stable engine management and long service life.

Key Features

• Heated oxygen sensor for downstream placement
• Specific fit for select Mazda 3 and Mazda 5 applications
• 4-wire design with female connector
• Threaded mounting type with 0.708 in. thread diameter
• 31.10 in. wiring harness length for application-specific routing
• OE Style replacement built for first-time fit

Detailed Product Description

The Denso 234-4390 oxygen sensor is designed for 2004-2005 Mazda 3 downstream applications and 2006-2007 Mazda 5 downstream applications. It also covers 2004-2005 Mazda 3 downstream models for Canada and except California configurations. As a direct replacement sensor, it helps maintain accurate exhaust feedback to the engine control system, which is important for fuel control and emissions monitoring.

This part cross-references Bosch 13770 and NTK 24232 for the same application. If you are replacing a worn downstream sensor on a Mazda 3 or Mazda 5, Denso 234-4390 provides an OE-style solution with the correct connector, wire count, and threaded fitment.

What This Oxygen Sensor Helps Address

• Check engine light related to downstream oxygen sensor performance
• Incorrect exhaust oxygen readings affecting fuel trim
• Reduced fuel economy caused by a failing sensor
• Slow or inaccurate sensor response in the exhaust system
• Emissions test failures tied to sensor degradation

Installation Notes and Tips

Verify the vehicle year, model, and downstream position before ordering. This sensor is a specific-fit part, so connector style, wire count, and thread size should match the original unit. Inspect the harness routing and exhaust bung condition before installation, and confirm the replacement is being installed in the correct downstream location on the Mazda 3 or Mazda 5.

Quality Assurance

Denso manufactures and tests this oxygen sensor to OE standards for replacement accuracy and consistent performance. The OE Style design is intended to deliver the correct fit and sensor function for the listed Mazda applications.