The following are the professional steps and precautions for replacing a NOx sensor:

1. Fault Confirmation and Pre-treatment
Reading the Fault Code
Use a diagnostic tool to connect to the OBD-II port and obtain the fault code (such as P2455 or P2456) to determine if the sensor hardware is damaged.
Wiring and Connector Inspection
Check the wiring harness for looseness, corrosion, or breaks. Use a multimeter to measure the voltage of the power and signal lines to ensure they meet specifications.
Reseat and reconnect the connector to ensure contact and clean any corroded areas.
Attempt to Reset and Clean

Turn off the vehicle power and gently pull the sensor wiring harness for one minute. Re-energize the power cord to see if the fault clears.

Wipe the probe surface clean of any carbon buildup using a special cleaner to avoid scratches from hard objects.

(Insert sensor cleaning/installation diagram here)

2. Replacement Procedure
Selecting the Matching Model
Use only genuine or certified replacement parts (check the vehicle model, year, and engine model).
Proper Removal and Installation

Disconnect the negative terminal of the battery. Avoid pulling violently on the wiring harness when removing the old sensor.

When installing a new sensor, align the threads and tighten according to the specified torque (usually 15-25 Nm).

(Insert sensor model selection guide card here)

Programming and Calibration
Connect a diagnostic device to perform sensor initialization programming.

Activate the sensor during a road test and verify the data flow (normal NOx level: 50-200 ppm for diesel vehicles).

III. Subsequent Maintenance Recommendations
Software Update: Check if the ECU has the latest software version to optimize sensor compatibility.
Preventative Maintenance: Change the air filter and engine oil regularly, and use low-sulfur fuel to reduce carbon deposits.

Important Note: Non-original sensors may cause data discrepancies. If the problem persists after replacement, investigate for exhaust leaks or SCR system issues.