Powertrain Control Module (Pcm)

Refer to COMPONENT INDEX .

PCM Cranking Management: Automatic Cranking - The term automatic cranking is referred to as every engine cranking that is not driven by an action on the ignition cycle that follows an automatic stop of the engine. When an engine cranking event has been decided by the PCM, the following PCM managed sequential procedure occurs:

• The PCM checks for an open torque path.
• The PCM closes the DBCR through a hard wired signal.
• The PCM closes its own cranking relay through a hard wired signal to close the starter control relay.
• When the engine is ON (RPM calibrated value detected of greater then 600), the PCM opens its own cranking relay.
• The PCM will detect and determine if the starter control relay circuit is connected or disconnected.
• The voltage in the starter control relay feedback is then measured and an average value is determined during this period. At this point the PCM checks that the its cranking relay is not stuck. Note that if the PCM relay is determined to be stuck, the PCM messages the BCM to turn off its cranking relay command, sends a status message over the bus indicating that the starter control relay is in fact stuck and then sets a DTC. However, if the PCM determines via voltage from the starter relay that the relay is not stuck, the PCM will not implement any further actions.
• The PCM will generate an internal signal and send that signal over the CAN-C network bus indicating the status and requests of the ESS system. The signals are used in order to tell the overall network nodes what is the ESS status.

• The PCM acquires the brake booster differential depression information from the ABS module.
• The PCM receives the brake pedal status and generates a brake position variable based on the inputs. The variables are:

  Brake Pedal Status - Input signal to the PCM:	PCM Variable generated - Brake Pedal Position:
  Pedal Released	HIGH
  Pedal Pressed	LOW
  Not Active	ERROR

• The PCM receives an internal signal from the APPS. This signal will generate an internal PCM variable indicating that the pedal position is HIGH if the throttle pedal is completely released.
• 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 crank sensor to remember the ESS engine stop position for a fast restart.
• The PCM will disengage the Air Conditioning (A/C) compressor clutch for a calibrated period of time following an ESS autostart event.

Clutch Pedal Position Sensor and the PCM: 

The PCM receives the clutch pedal position switch information. The clutch position sensor is used to determine the clutch pedal position. The PCM obtains the sensor position information from the sensor using a hard wired connection. The PCM then takes the sensor information and transmits the clutch position over the CAN bus network. If the PCM detects a fault on the clutch position sensor or the integral clutch interlock switch, the PCM will disable ESS system events.

Dual Gear Position Detection Sensors (GPDS) and the PCM: 

The PCM also interfaces with the GPDS system when equipped on MTX vehicles. The PCM uses the dual GPDS gear position signal in the ESS system during ESS autostop and ESS autostart events. The calculated gear position also has the potential to inhibit the ESS system operation, depending on the detected gear. This is managed from within the PCM as the PCM is the main ESS system controller.

Neutral Position Sensor (NPS) and the PCM: 

If the vehicle is equipped with a NPS instead of the GPDS, the PCM uses the NPS to provide an output from the sensor to the PCM concerning gear range position. On MTX equipped vehicles, the shift cable position is interpreted by the PCM from the NPS to determine if the transmission is in NEUTRAL. This is done for the purpose of determining when the ESS system can safely restart the vehicle without the clutch pedal being depressed. The switch outputs a PWM signal whose percentage of duty cycle corresponds to the range denoted in NEUTRAL, in a gear range, or as a fault value. The NPS is nominally outputting 50% duty cycle at or when the vehicle is shifted to NEUTRAL. Higher or lower duty cycle outputs are denoted as the magnet on the shift cable moves with respect to the NPS when the vehicle is shifted to a gear range position. The NPS receives a 5 volt excitation input from the PCM. The NPS has a common ground.

Driver Presence Detection Module (DPDM) and the PCM: 

The DPDM, located in the drivers front seat, is responsible for detecting whether or not the driver front 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 autostop and ESS autostart events. The DPDM is used if the vehicle is not equipped with a door ajar sensor.

The PCM determines the status of the driver occupancy presence based on CAN-C network bus messages received from the DPDM. If the PCM detects a fault from the signals bussed from the DPDM, the PCM will inhibit the ESS system in MTX equipped vehicles. If the PCM recognizes a DPDM fault during an ESS autostop event, the PCM will force an ESS autostart event to occur.

In ATX equipped vehicles, if the PCM recognizes a DPDM failure during an ESS Autostop 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 Autostart.

If the PCM recognizes a DPDM fault during an ESS Autostop event, the PCM will secure the vehicle by requesting a Shift to Park from TCM and requires correction of shifter and Key Start.

Hood Ajar Switch and the PCM: 

• For hood ajar switch #1, the PCM provides a rationality check by comparing the state of the hood ajar switch #1 to the state of the hood ajar switch #2. This diagnostic will be performed at very low speeds just prior to engine shut down to minimize any possibility of vehicle bounce causing potential false indication of each hood ajar switch state. The PCM also provides diagnostics for short circuit to ground, short circuit to open, and short circuit to power for the hood ajar switch #1. If the hood is open or if there is a rationality issue between the two hood switches, the engine shutdown will be maintained and engine restart will require shifting the vehicle to PARK or NEUTRAL and an ignition cycle. Note that hood ajar switch #1 uses a CAN bus communication signal.
• For hood ajar switch #2, the PCM provides a rationality check by comparing the state of the hood ajar switch #2 to the state of the hood ajar switch #1. The PCM provides diagnostics for short circuit to ground, short circuit to open, and short circuit to power for the hood ajar switch #2. If the hood is open or if there is a rationality issue between the two hood switches, the engine shutdown will be maintained and engine restart will require shifting the vehicle to PARK or NEUTRAL and an ignition cycle. Note that hood ajar switch #2 uses a hard wired signal to the PCM to communicate.
• The PCM performs a hood ajar switch rationality check by comparing the state of the hood ajar switch #2 to the state of the hood ajar switch #1. This is performed above a calibrated vehicle speed value and determines if either switch is faulted. If both switches are reading differently, the switches will fault and inhibit the ESS system from functioning.