Brake Switch Signal

Description
The brake switch inputs from the hall switch are normally low voltage into the ECM, but when the brake pedal is pressed, these inputs are raised high to approximately battery positive. The ECM requires the input of the brake switch to judge the current vehicle state. This is required to do some calculations in order to calibrate the monitoring concept required for drive by wire vehicles. There are also other calibration modules such as driveability (surge damping etc) which look at the state of the brake switch in order to judge the best set up for the driver in that situation. Another vital user is the cruise control system, which on receipt of high brake switch signals, cancels cruise and returns control of the vehicle to the driver.

The ECM performs a series of diagnostics tests on the brake switch and if it is deemed faulty at any time, the ECM will cancel cruise and disallow further operation until the fault has been fixed and an ignition reset has occurred. A fault is detected if the battery voltage is greater than 10 V and the state of the brakes switches is different, i.e. the Brake Light Switch (BLS) = on and the Brake Test Switch (BTS) = off.