Body Control Module (BCM)

A modified BCM is used for communications and starter relay 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.

When an automatic cranking event (automatic cranking is defined as every engine cranking event that is not driven by an action on ignition status and that follows an ESS event) has been decided by the PCM, the cranking procedure is thereafter managed by the BCM as follows:

• When the BCM receives the starter relay control "No action" command signal from the PCM, the BCM opens its own cranking relay by means of a hard wired signal to open that starter control relay.
• If the BCM instead receives the "action" command signal from the PCM, then the BCM closes its own cranking relay by means of a hard wired control signal to the starter control relay to close.

The BCM receives a CAN-Interior High Speed (CAN-IHS) network bus message from the HVAC module if the HVAC module determines that the condition for an ESS event must be disabled for HVAC usage. The BCM gates the signal from HVAC to PCM to inhibit an Autostop. PCM will inhibit ESS events until HVAC module is able to perform properly during an Autostop.

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.

The BCM receives a fuel level sensor message in the form of bussed message with a voltage reading that indicates how much fuel is in the tank.

Door Ajar Switch Management by the BCM: 

The ajar switches are hard wired to the BCM which receives analog voltage values that are gated over to the PCM. The BCM converts the voltage value into counts, where each count represents a specific voltage range. The PCM receives these signals and diagnosis the count. Once diagnosed, the PCM sets the status indicating Open, Closed, Shorted High, or Shorted Low. The appropriate DTCs will then be set.

The BCM monitors the door ajar switches using door transition monitor signals. These signals watch for a door transition from Open to Closed or Closed to Open. This monitoring is also performed during ignition off as well. If a transition occurs, the signal is set to transitioned and sends the signals over to the PCM, otherwise, the signal no transition is set. The BCM clears this status at Key OFF and begins the monitoring process once more. The PCM receives this status and checks to see if the ignition off timer has exceeded a calibrated threshold. If no transition occurs, and the ignition timer has been off long enough, a failed counter is incremented by a value of one. This represents one trip without a transition. At any time during that a transition occurs, the counter is reset to zero. If the counter exceeds a certain number of trips, a DTC is posted and the ESS system is now inhibited.

For vehicles that utilize two door switches, a coherency check between the two switches is performed. The check will compare the status of both switches, as well as the transition monitors for each respective switch. A failed comparison will result in ESS system inhibition. In the event that this occurs during an ESS autostop, this failure will inhibit the ESS autostart function. Raw data from both of the door switches are also compared with a calibrated threshold to check if any of the switches are faulted on the high or the low side. If algorithm determines that there is a failure in either of the switches, the PCM will post a DTC and the ESS autostop events will be inhibited.