The NGK SA16254 is a genuine 4-wire oxygen sensor designed for optimal engine performance and emissions control in various John Deere 4R Series utility tractors, including models 4044R, 4052R, 4066R, 4075R, and 4078R. This M18 x 1.5 thread sensor provides accurate exhaust gas oxygen readings to the engine control unit (ECU), ensuring efficient fuel mixture and reliable operation. It serves as a direct replacement for John Deere part number RE520957, offering OE-quality reliability and performance.