1993 Audi S4 Wheel Speed Sensor Replacement Cost

They are mounted in the hub, close to the brake calipers, where they can monitor how fast the axles are turning. All four WSS work in unison by providing four independent signals to the ABS control module, which allows the control module to correct for slipping if one or more wheels stop rotating. This action is responsible for highly reduced braking distances in slippery conditions.

In the event that a wheel speed sensor fails, the ABS, traction control system (TCS) and manufacturer specific stability control system lights will illuminate, informing the driver that the systems are disabled. The vehicle will be more prone to tire slip, and normal driving patterns may need to be adjusted to correct for the loss of computer control. On older vehicle's, the speedometer can be affected, causing illumination of the check engine light as well.

The vehicle can be driven with these warning lights on, since failure of the ABS or TCS does not disable the vehicle, but safety is a concern as drivers become accustomed to the road manners of their vehicle's. If hard braking that is normally controlled by the ABS control module is necessary, a collision may occur. We do recommend towing the vehicle to a repair facility if braking feels unusual under light or normal driving conditions.

Wheel speed sensors are notorious for failure, since they are housed on the wheel hub, near the road surface. This means the sensor and electrical connections are subject to dust, debris, precipitation, salt, and road hazards. Aside from that, brake dust and road grime are known to accumulate around the magnetic sensor, causing interference, and preventing proper readings. If the ABS and TCS lights are active, there is a very good chance you have a faulty wheel sensor, without regard to mileage.

Anti-lock braking systems are complex, and are typically diagnosed through professional computer scanning equipment, or manufacturer specific software. The technician will communicate with the ABS control module via computer, and view real-time data to determine what fault has been detected, and how the system is behaving. Once the technician identifies a suspected wheel speed sensor failure, physical inspection and probing will take place to ensure an accurate diagnosis. This includes inspecting the tip of the sensor for dirt and debris.

Wheel sensor replacement is done by disconnecting the electrical connectors, and unscrewing the sensor from the wheel hub. On some models, the wheel sensor is non-serviceable, and the entire hub must be replaced. This involves removing the wheel, brakes, drive axles, if needed, and finally the wheel hub and bearing assembly. The lower ball joint will need to be disconnected from the steering spindle or lower control arm to allow the drive axle to move freely away from the wheel hub and bearing assembly.

While inspecting and testing wheel sensors, the wheels may be removed from the vehicle, allowing the servicing technician to inspect brake and tire wear, as well as suspension components. Also, if the wheel speed sensor is determined to be malfunctioning due to dust and grime buildup, consider having the other wheel speed sensors examined to prevent future unexpected failures.

The wheel speed sensor is the most basic component in the ABS system, and the most likely to fail. The cost of a wheel sensor repair can be negligible, but if the sensor is non-serviceable the cost will rise dramatically as the mentioned disassembly and reassembly is required.

Wheel speed sensors can be changed by the DIYer, but diagnosis should be left to a professional for time and cost savings. The cost of diagnostics is often less than replacing the wrong part, especially if the ABS light is on for a reason other than the wheel sensor. If speed sensor replacement requires wheel hub and bearing assembly removal, consider letting a certified repair facility complete the repair.