9-3 Convertible (9400) L4-2.0L Turbo (B205) (2000)
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Brake Switch (Cruise Control): Description and Operation
Brake Lights Switch
Brake Lights Switch
When the brake pedal is depressed the brake lights switch closes and control module terminal 7 (G) is supplied with B+, i.e. about 12 V, from fuse 12.
Terminal 7 (G) must be grounded via the brake light bulbs for the cruise control to be operative.
The control module knows that the voltage applied to terminal 7 (G) is 12 V because the input is provided with an ND converter which actually measures
the voltage. When the brake lights switch is not activated, the control module's input is grounded via the brake light filaments and the voltage applied to
the control module input is 0 V. This system is employed to ensure that the control module really is connected to the brake lights circuit.
In the event of a break in the supply of current to control module input 7 (G), the A/D converter senses that the voltage is appreciably higher than ground
but lower than B+. The cruise control will then be inoperative because an important input lacks relevant information.
