Powertrain Control Module (Pcm)

During the initial engine cranking event, the PCM energizes the PCM controlled starter relay 1 using a low side driver control. When the engine is started (RPM calibrated value detected of greater then 600), the PCM switches off the low side driver control and opens the relay. The PCM monitors the output from the relay through the Crank Sense circuit. The Crank Sense circuit is spliced to the starter relay output inside the Power Distribution Center (PDC) and hard-wired directly to the PCM. The PCM sends ESS commands to the eTorque system for all subsequent Engine Stop/Start (ESS) auto-start events. 

The PCM monitors several hard-wired and CAN message inputs to determine the functionality of the ESS system.

• Crankshaft Position (CKP) Sensor  - In order to protect the engine against damage caused by inadvertently sparking a cylinder following a rollback condition, the PCM utilizes a control that effectively turns off the fuel and spark drivers when below a given RPM. The PCM also utilizes a bidirectional CKP sensor to determine the ESS engine stop position for a fast restart.
• Brake Pedal Position (BPP) Sensor  - The brake pedal position sensor signal is acquired over the CAN bus from the Brake System Module. The PCM monitors the BPP sensor signal to determine the brake pedal position. The BPP sensor min/max travel thresholds are a learned value in the PCM. The PCM must perceived the pedal position pressed to allow an auto-stop. When the BPP sensor signal transitions towards the released state the PCM will auto-start the engine.
• Accelerator Pedal Position (APP) Sensor  - The APP sensor is hard-wired to the PCM. The PCM will only allow an auto-stop when the sensor signal indicates no throttle input is present. If the PCM detects accelerator pedal input during an auto-stop event, the PCM will auto-start the engine.
• Drivers Seat Belt Switch  - The Occupant Restraint Controller (ORC) sends a message with the state of the drivers seat belt over the bus to the PCM. ESS is disabled if the drivers seat belt is not latched.
• Driver Presence Detection Module (DPDM)  - The DPDM, located in the drivers front seat, is responsible for detecting whether the front driver side seat is occupied or unoccupied by the vehicle operator. The signals generated by the DPDM are influential on how the ESS system will operate during ESS auto-stop and ESS auto-start events. The DPDM is used on vehicles that are not equipped with a door ajar sensor. In ATX equipped vehicles, if the PCM recognizes a DPDM failure during an ESS auto-stop event, the PCM will secure the vehicle by requesting a Shift to Park from the TCM and then requires correction of shifter moving out of Park before the engine will auto-start. The PCM determines the status of the driver occupancy presence based on CAN C network bus message received from the DPDM. If the PCM detects a fault in the DPDM bussed signal, the PCM will inhibit the ESS system in MTX equipped vehicles. If the PCM recognizes a DPDM fault during an ESS auto-stop event, the PCM will force an ESS auto-start event to occur.
• Hood Ajar Switches  - ESS vehicles are equipped with two hood ajar switches for redundancy. Hood ajar switch 1 signal is a bussed signal from the Body Control Module (BCM). Hood ajar switch 2 is a hard-wired input to the PCM. The PCM performs a rationality check of the two signals. If the input signals do not match, or indicate that the hood is ajar, the PCM will not allow an auto-stop event. If this occurs during an auto-stop event, the transmission must be shifter to park or neutral and manually restarted.

The PCM will send messages over the CAN C network bus indicating the status and requests of the ESS system. The signals are used in order to inform the overall network nodes the ESS status.