Denso 4099 Spark Plug

Denso 4099 U-Groove Spark Plug

Denso 4099 is a conventional spark plug built for reliable secondary ignition performance in applications that call for a 12 mm, flat-seat plug with a 19.00 mm reach. Its U-Groove ground electrode design promotes stronger ignitability for cleaner combustion and improved engine efficiency.

For drivers searching for a Denso spark plug for Honda Civic, Toyota Corolla, or other import engine applications, this part number 4099 offers an OE-style replacement format with a copper core center electrode and nickel tip materials.

Key Features

• U-Groove ground electrode tip design for improved spark exposure
• Conventional spark plug construction for standard ignition service
• Copper core center electrode for stable heat transfer
• Nickel center and ground electrode tip materials
• Pre-gapped to 0.7 for installation consistency
• 12.00 mm thread diameter, 19.00 mm reach, and flat seat type
• 18.0 mm hex size for proper socket fitment
• Manufacturer heat range 24

Product Details

The Denso U-Groove Conventional line focuses on dependable ignition performance with a ground electrode shape that helps expose the spark kernel more effectively. On part number 4099, the nickel U-groove ground electrode works with a copper-core center electrode to support consistent firing characteristics in everyday driving conditions. This spark plug is a practical choice for import vehicle maintenance where the correct thread diameter, reach, seat type, and heat range matter for proper engine operation.

This part cross-references DENSO Auto Parts X24ES-U for the same application.

Common Issues This Part Addresses

• Hard starting caused by worn or inefficient spark plugs
• Rough idle from weak or inconsistent ignition output
• Misfire conditions related to degraded plug electrodes
• Reduced fuel efficiency from incomplete combustion
• Loss of throttle response from aging secondary ignition components

Installation Notes and Tips

Verify the thread diameter, reach, seat type, and hex size before installation. Denso 4099 is pre-gapped to 0.7, but the gap should still be checked against the vehicle service specification before use. Use the correct torque procedure for the cylinder head material and confirm the plug is appropriate for the engine’s heat range requirements. For Honda Civic, Toyota Corolla, and similar import applications, matching the OE-style dimensions is essential for proper sealing and combustion chamber fit.

Quality Assurance

Denso is a recognized ignition component manufacturer, and the U-Groove Conventional product line is built around practical OE-style service requirements for secondary ignition systems. Part number 4099 is specified with defined electrode materials, dimensions, and heat range to support accurate replacement selection.