Diagram reference number 2 in the image below:
" Fitment: 2006 NISSAN FRONTIER XE - 4 door

Application Notes: Exc.Off Road Package

Category: Tire and Wheel

SubCategory: Tire

Position: General

Part Number: 40702CK002


This is a Tire Pressure Monitoring System (TPMS) Sensor Grommet that fits the 2006 NISSAN FRONTIER XE - 4 door with the QR25DE engine. The Tire Pressure Monitoring System (TPMS) Sensor Grommet is designed by NISSAN to be part of the Tire and Wheel-Tire. The Tire Pressure Monitoring System (TPMS) Sensor Grommet has a position on the vehicle of General. The 2006 NISSAN FRONTIER Tire Pressure Monitoring System (TPMS) Sensor Grommet is a factory made NISSAN OEM part and it comes with a 12 month 12,000 mile warranty (parts only). Do not be fooled by an aftermarket NISSAN FRONTIER Tire Pressure Monitoring System (TPMS) Sensor Grommet! Buy a factory NISSAN part and receive peace of mind!
This factory part has a part number of 40702CK002.