Functional Description - Body Control Module

During the initial engine cranking event, when the BCM receives a crank signal from the Powertrain Control Module (PCM), the BCM energizes the BCM controlled starter relay with an internal high side driver control.

The BCM is the gateway for all bus communications needing to be gated from one bus network to a different bus network. This grants the modules on different busses the ability to interact with each other. If the Local Interface Network (LIN) or CAN bus communications go down, the BCM will set the appropriate DTCs and display SNA values.

The BCM receives the state of the START/STOP Off switch in two signals over the CAN-IHS bus network from the ICS switch bank. The BCM then gates and routes those signals to the PCM.

The BCM will control the START/STOP Off switch illumination via a CAN-IHS bus message received by the ICS switch bank from the BCM.

Door Ajar Latch Switches  - The ajar switches are hard-wired to the BCM. The BCM broadcasts the switch state over the CAN bus to the PCM.

Functional Operation of the Door Ajar Latch Switches: 

All of the Door Latches are monitored to determine if they are closed or ajar. All of the ajar switches are wake-up signals to the BCM. The Driver Door Latch must be rationalized in order for some vehicle features to function. Unlike the passenger ajar signals that function like traditional open/closed ajar switches, the Driver Door Latch has redundant switches and signals for diagnostic purposes. The two switches share a common sensor ground. The Door Ajar Switch signals use Battery voltage for a reference. The switches operate in the following manner:

• Driver Door Ajar Switches:  The BCM has an internal pull up 1000 Ohm resistor for each ajar signal. Each switch has an internal 604 Ohm and 1070 Ohm resistor. When the switches are open the resistance through the switches are 1674 Ohms. When the switches are closed the resistance through the switches are 604 Ohms. The switch states are opposing each other, meaning that when the door latch is closed  , switch 1 is in the open state and switch 2 is in the closed state. The opposite is true when the door latch is opened  . For more information refer to the tables below.
• Passenger Ajar Switches:  The ajar switches are open when the latch is closed. When the door latch is ajar the switch closes allowing the signal to connect to ground through the switch. Therefore the signal inputs to the BCM are high when the door is closed and low when the door is ajar.

The resistors in the latch switches allows the BCM to perform diagnostics on the circuits and switches. Unlike the passenger door switches the voltage on the two signals should not be high or low. If the BCM determines that either signal falls into the high or low range, a fault is set. If the door latch positions do not match between the two Driver Door Ajar Switches, a correlation fault will set.

If the door is ajar, or a fault is detected, the ESS system is inhibited. In the event that this occurs during an ESS auto-stop, this failure will inhibit the ESS auto-start function.