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Wheel Speed Sensors (WSS)

Wheel speed sensors are now critical components in the accurate operation of ABS, Traction Control, Vehicle Speed, Transmission Control, Stability Control, Hill Descent, ADAS Engine Management and even Navigation systems.

Wheel speed sensors, like most Automotive sensors operate in harsh environments, high temperatures, contamination from water, dirt and even brake dust can cause premature failure of a sensor physically and electrically.

Failures can also happen when the vehicle is being worked on. Some of the common causes of failures include wiring breaks, contamination and damaged caused by excessive wheel bearing clearance or damage to Tone rings or Pick-up wheels whilst servicing brake systems is possible.

Symptoms of a Faulty Wheel Speed Sensor

The driver of a vehicle with a faulty Wheel Speed Sensor may report to the workshop one or more of the following symptoms

Multiple warning lights displayed on the dash
The wheels lock during braking
Pulsation of the brake pedal
Erratic or No speedometer operation
Other seemingly, unrelated system failures

Trouble Shooting and Diagnostics

When trouble shooting a vehicle, you first need to identify if the suspect sensor is an Inductive or Active sensor. From the late 90’s vehicle manufacturers have mainly fitted active sensors due to their superior accuracy at very low speeds and some with the ability to indicate reverse rotation. Inductive and active sensors look similar, so it is difficult to differentiate them. If unsure it is important to refer to the vehicle manufacturer specifications and procedures. Generally, Active Sensors require a supply voltage and Inductive sensors do not.

In most situations the vehicle will present with a warning light illuminated on the dash for ABS, TCS or ESP. The following checks should be performed

Using a suitable diagnostic tool read the fault codes
Inspect the wiring
Inspect the mechanical assemblies
>Check output signal using a scope or suitable diagnostic tool
Check supply voltage (Active sensors)
Check sensor resistance (Inductive sensors)

Development of Wheel speed sensors has significantly advanced, and the evolution of all systems will continue. PAT are constantly working with OE suppliers and manufacturers to ensure we stay up to date with the latest technologies including electric vehicles. This constant research and development allows PAT to have the parts and technical knowledge available to our clients as transportation evolves.

MERC FRONT WHEEL SENSOR

MERC FRONT WHEEL SENSOR