Powertrain Control Module (Pcm)
WARNING: This page is about a different variant/trim than selected.
During the initial engine cranking event, the PCM energizes the PCM controlled starter relay 1 with an internal 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 see 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.
Not all vehicles are equipped with manual transmissions. Also, the sensors used can vary between vehicles. Listed below are all of the devices that can be used for monitoring inputs on manual transmission equipped vehicles. Check the wiring information to determine which devices are used on the vehicle that is being serviced.
- Clutch Pedal Position Sensor
- On vehicles equipped with a manual transmission, the PCM monitors the Clutch Pedal Position Sensor signal to determine when to allow an auto-stop and auto-start event. The clutch pedal position sensor is a learned value. The PCM also learns the clutch engagement point. The graphic below shows the PCM interpretation of the signal. Vehicles equipped with ESS will also have a Clutch Interlock Switch. The Clutch Interlock Switch is different than the traditional Clutch Pedal Switches in that it only detects the interlock (pedal depressed) position. The switch input is compared to the Clutch Position Sensor signal for the correlation diagnostic. If a correlation fault sets it will affect the ESS system in one of the following ways:
- If the fault occurs prior to an auto-stop, ESS will be disabled and no auto-stop will occur.
- If the fault occurs during an auto-stop with the transmission in neutral, the vehicle will auto-stop and ESS will then be disabled.
- If the fault occurs during an auto-stop with the transmission in gear, vehicle will not start until the shifter is moved into neutral and then ESS will be disabled.
- Gearshift Position Sensor
- Some vehicles that are equipped with a manual transmission have a gearshift position sensor. The PCM uses the gearshift position sensor in the ESS system during ESS auto-stop and ESS auto-start 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. The gearshift position sensor has a shared 5.0 volt supply, sensor ground and two position signals from the sensor. The signals to the PCM are in the form of a 5.0 volt square wave duty cycle. The gearshift position sensor quadrants are learned at the plant. These positions will need to be learned if the sensor, or any Transmission Shifter components are replaced. The PCM monitors movement of the shifter along the X and Y axis to determine the shifter position. The X axis is left and right movement of the shifter which detects 4 different quadrants. The Y axis is forward and backward movement of the shifter which detects 3 different quadrants. The PCM uses the two duty cycle signals to make the determination of the shifter position. See the graph in the illustration below depicting the gear shifter positions and correlating duty cycles.
The normal operating duty cycle range for each signal is between 10% and 90%. If the PCM detects that the duty cycle for either signal is above or below the normal duty cycle range a circuit fault will set. The PCM also monitors the rationality of the shifter position by comparing the actual gear shift position feedback to the calculated gear shift position. The gear shift position calculation is based on the transmission being in a forward gear with the clutch pedal not pressed, vehicle speed, engine speed, and calculated engine torque.
- Neutral Position Sensor - Some manual transmission equipped vehicles have a neutral position sensor instead of a gearshift position sensor. On these vehicles the PCM is only monitoring for the transmission to be in the neutral position or in any gear position. This is done for the purpose of determining when the ESS system can safely restart the vehicle without the clutch pedal being depressed. The neutral position sensor outputs a PWM signal. The sensor signal will typically be around 50% duty cycle when the shifter is in the neutral position. A duty cycle other than approximately 50% indicates that the shifter is is shifted to a gear range position.
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.