Denso 3403 Spark Plug

Denso Iridium Long Life Spark Plug 3403

Denso 3403 is an Iridium Long Life spark plug built for OE-level performance, durability, and emissions standards. It uses an iridium center electrode with a platinum chip ground tip to support stable ignition performance and long service life in a wide range of import and domestic applications.

Key Features

• Iridium center electrode tip for consistent spark delivery
• Platinum chip ground electrode tip design for extended wear resistance
• 5000 ohm resistor for ignition noise suppression
• 0.8 mm pre-gap for OE-style setup
• 14 mm thread diameter, 19.00 mm reach, and flat seat design
• Nickel ground electrode core with copper center electrode core
• Manufactured to OE performance, durability, and emissions standards

Product Details

The Denso Iridium Long Life line is engineered for drivers who want OE-style ignition consistency and long-term electrode stability. Part number 3403 combines an iridium center electrode tip with a platinum chip ground design, helping maintain reliable spark characteristics under daily driving conditions. This spark plug is a direct replacement choice for many vehicles, including Mercedes-Benz S65 AMG, Chevrolet Cruze, and Volkswagen Jetta applications listed in the fitment data. Denso 3403 is also referenced across multiple OEM part numbers for the same application, including DENSO Auto Parts SK20PR-A8 and General Motors 55580961.

What It Helps Address

• Rough idle caused by worn spark plugs
• Hard starting from weak ignition output
• Misfire conditions related to electrode wear
• Reduced fuel economy from inconsistent combustion
• Emissions issues tied to degraded spark performance

Installation Notes and Tips

Verify thread diameter, reach, seat type, and heat range before installation. This plug uses a flat seat, 14.00 mm thread diameter, 19.00 mm reach, and 16.0 mm hex size. Check the vehicle service information for the correct gap specification and torque procedure, and inspect ignition coils, boots, and wires during replacement. Fitment includes applications such as 2013-2015 Chevrolet Cruze, 2008-2010 Volkswagen GTI, and 2017-2020 Mercedes-Benz S65 AMG; some Mercedes-Benz applications note that two spark plugs are required per cylinder in the vehicle listing.

Quality Assurance

Denso manufactures this spark plug to strict OE performance, durability, and emissions standards. The Iridium Long Life design is built around durable electrode materials and OE-style dimensions for consistent service in the listed applications. This part cross-references DENSO Auto Parts SK20PR-A8 and General Motors 55580961 for the same application.