Circuit/System Description

WARNING: This page is about a different car, the 2022 Cadillac CT5. However, it is still accessible from the selected car via links, so may be relevant.

The S38 On/Off Vehicle Switch contains two individual switches that provide redundant switch inputs to both the K9 Body Control Module (BCM) (Power Mode Master) and the K56 Serial Data Gateway Module (Back Up Power Mode Master).

The K56 Serial Data Gateway Module supplies the S38 On/Off Vehicle Switch with a 5 V on signal circuit 3558 while the module is awake & low reference circuit 3559. The K56 Serial Data Gateway Module monitors this signal to determine if the switch is released or pressed. When the S38 On/Off Vehicle Switch is not pressed, voltage on the signal circuit 3558 is pulled down through two resistors in the switch by low reference circuit 3559. When the S38 On/Off Vehicle Switch is pressed, voltage on the signal circuit 3558 is pulled down through only one resistor in the switch by low reference circuit 3559, the changing the voltage seen at the K56 Serial Data Gateway Module indicates that the S38 On/Off Vehicle Switch is pressed. The K56 Serial Data Gateway Module is the vehicles backup power mode master. If a fault is detected on signal circuit 3558 or low reference circuit 3559 a DTC will set.

The K9 Body Control Module supplies the S38 On/Off Vehicle Switch a constant 5 V signal on Signal Circuit 5723. The K9 Body Control Module monitors this signal to determine if the switch is released or pressed. When the S38 On/Off Vehicle Switch is not pressed, voltage on the signal circuit 5723 is pulled down through two resistors in the switch by ground circuit 1351. When the S38 On/Off Vehicle Switch is pressed, voltage on the signal circuit 5723 is pulled down through only one resistor by ground circuit 1351, the voltage change seen by the K9 Body Control Module indicates that the S38 On/Off Vehicle Switch is pressed. If a fault is detected on signal circuit 5723 or ground circuit 1351 a DTC will set.

The S38 On/Off Vehicle Switch has two LEDs that indicate the vehicle power mode. When the vehicle is in the off mode, both LEDs will be off. Pressing the S38 On/Off Vehicle Switch button momentarily without the brake pedal applied, the vehicle will enter the accessory mode, the K9 Body Control Module supplies a pulse width modulated voltage on control circuit 5720 to illuminate the amber LED (accessory), the LED is grounded through the switch by ground circuit 1351. The accessory mode has a time-out up to 5 min to help reduce battery drain. Pressing and holding the push button start switch without the brake pedal applied for 5 s will place the vehicle in Run Mode (Ignition On without the Propulsion Mode), the K9 Body Control Module supplies a pulse width modulated voltage on control circuit 5719 to illuminate the green LED (Run/Start/Propulsion), the LED is grounded through the switch by ground circuit 1351. With the ignition off brake pedal applied, pressing the S38 On/Off Vehicle Switch button once, the vehicle will enter Vehicle Start/Propulsion Mode this will start the Propulsion system, the K9 Body Control Module supplies a pulse width modulated voltage on control circuit 5719 to illuminate the green LED (Run/Start), the LED is grounded through the switch by ground circuit 1351.

If the vehicle is in Propulsion Mode and vehicle speed above 4 km/h (2.5 mph) is detected and the S38 On/Off Vehicle Switch is pressed for greater than 2 s or is pressed 2 times within 5 s the vehicle will enter the Run Mode (Ignition On without the Propulsion Mode).