Front-wheel sensors: Notes
The front left wheel sensor sends a wheel-speed signal to pin 7 on the control module. The sensor is grounded via pin 6.
The front right wheel sensor sends a wheel-speed signal to pin 5 on the control module. The sensor is grounded via pin 3.
Mounted on the right-hand and left-hand outboard drive shaft CV joints is a toothed wheel with 29 teeth. A sensor of inductive type is mounted on each steering swivel member. The gap between sensor and toothed wheel must be 0.3-1.3 mm and is not adjustable.
The inductive sensor works like a small alternator, the sine-wave voltage of which increases with increasing wheel speed. The sine-wave voltage alternates between positive and negative polarity, which is achieved by alternate teeth and gaps on the toothed wheel.
By measuring the frequency, the control module can determine the speed of each wheel.
A wheel speed of 20 km/h (12.5 mph) will give approximately 2 V AC 70 Hz
The TC/ABS control module uses this wheel-speed information for:
- calculating wheel acceleration (speed increase), wheel retardation (speed reduction) and the car's reference speed, which is normally measured on the fastest rear wheel.
- comparing the wheel speed of the rear wheels as a basis for determining whether the car is being driven straight ahead or round a bend.
- calculating wheel slip on retardation and wheel spin on acceleration. If the limit is exceeded, ABS or TCS modulation will be activated.