Audi NOx Sensor SNS451 12V Ceramic Chip 4G0907807S Emission Control

Audi-specific SNS451 NOx sensor, using 12V ceramic core technology; OEM number 4G0907807S; direct replacement for original part. Installed near the SCR catalyst in the exhaust system; continuously monitors NOx in exhaust and transmits data to the ECU to regulate urea injection to maintain emissions compliance. Compatible with Audi A4, A5, Q5 with 2.0T or 3.0T diesel engines. Installation difficulty: medium; labor about 1.5 hours. Pay particular attention to wiring harness routing to avoid signal interference. If the vehicle shows “Check Engine,” abnormal urea consumption, weak acceleration, or emissions out of spec, sensor aging is likely.