Stop lights switch

1. Sensor
2. Phonic wheel
3. Hub
4. Brake drum
5. Suspension arm

If one or more phonic wheels break or become deformed, causing a difference in speed of 25% in relation to the reference speed, the electronic control unit switches off the device and switches on the fault warning light. The time for detecting the fault is about 120 seconds with a vehicle speed of over 6 km/h.

NOTE Whenever fitting an rpm sensor, smear it with water-repellent grease, otherwise it could be damaged during subsequent withdrawal as a result of temperature variations over a period of time.

STOP LIGHTS SWITCH

The signal that the brake pedal has been operated reaches the control unit by the connection of the switch (1) controlling the stop lights to pin 12.

This information is useful not only for controlling braking, but also under particular conditions, for example if sudden acceleration which makes the wheels skid is followed by heavy braking, or in the case of rough road surfaces (bumps etc.) which could cause variations in wheel speed for reasons not associated with the braking in progress.

Under these conditions the microprocessors work out a strategy linked to the changes in wheel speed at these moments, ensuring that braking is within correct parameters. As these are particular circumstances of braking control, the efficiency of the system is not impaired if the brake pedal switch is not connected to the control unit. For this reason it is not indicated by the warning light coming on, nor is the A.B.S. disabled.