Q: How do you diagnose and replace a faulty ABS Sensor on Nissan Armada?A: On most road surfaces, the antilock brake system ( ABS ) was developed to sustain vehicle steerability , directional stability and excellent deceleration. It has three basic components which are wheel speed sensors, electronic control unit ( ECU ) and hydraulic unit. In order to prevent wheel lock up during braking, the ABS system monitors rotational speeds of each wheel and regulates brake line pressure to each wheel. In case something goes wrong, an "ABS" warning light illuminates on the dashboard. Preliminary checks such as checking brake fluid level, verifying electrical connectors, inspecting fuses and wiring harness are some of the ways through which you can use to diagnose and repair your ABS system. If this does not solve the problem it is advisable to have a qualified automotive technician diagnose it for you. With a damaged or faulty wheel speed sensor it can be replaced by disconnecting the electrical harness, remove mounting bolt and carefully pull out sensor without using pry tool or pulling by wire harness. When reinstalling the ABS sensor always ensure that you replace the O-ring with a new one and tighten down the mounting bolt to proper torque specification.