Engine Stop Start System

DESCRIPTION 

Courtesy of CHRYSLER GROUP, LLC

The following list indicates some of the components involved in the Engine Stop Start (ESS) system:

1.	Refer to POWERTRAIN CONTROL MODULE (PCM) .
2.	Refer to GENERATOR .
3.	Refer to INTELLIGENT BATTERY SENSOR (IBS) .
4.	Refer to MAIN AND AUXILIARY BATTERY .
5.	Refer to STARTER MOTOR RELAY  - Located within the main Power Distribution Center (PDC).
6.	Refer to INSTRUMENT PANEL CLUSTER (IPC) .
7.	Refer to START/STOP OFF SWITCH  - Integral to the Integrated Center Stack (ICS).
8.	Refer to RADIO FREQUENCY HUB .
9.	Refer to BODY CONTROL MODULE (BCM) .
10.	Refer to MAIN AND AUXILIARY BATTERY .
11.	Refer to TRANSMISSION CONTROL MODULE (TCM)  - Automatic Transmissions (ATX) only.
12	Refer to STARTER MOTOR .
13	Refer to ANTI-LOCK BRAKE SYSTEM (ABS) MODULE .
-	Refer to POTENTIAL ESS SYSTEM INHIBITORS .

The ESS system automatically stops and starts the engine when certain conditions are met to improve fuel economy and lower Carbon Dioxide (CO2) emissions. The START/STOP Off switch is integral to the ICS.

The Battery, Starting and Charging systems operate in conjunction with one another, and must be tested as a complete system. For correct operation of starting/charging systems, all components used in these three systems must perform within specifications. When attempting to diagnose any of these systems, it is important that you keep their interdependency in mind.

Certain starting system components and functions of the ESS system are On Board Diagnostics (OBD) II monitored and will produce Diagnostic Trouble Codes (DTC). The use of the diagnostic scan tool is not only recommended, but it is necessary for proper diagnosing of the ESS system and the components or systems that are related to ESS system functions. Review the component and system information listed below in the operation information for diagnostic information. Otherwise, review the appropriate wiring information.

OPERATION 

The vehicles first engine crank event is managed by the driver acting on the ignition state and requesting an engine crank request. When this request occurs, the BCM cranking relay is opened and the PCM cranking relay is closed. When the engine is ON and the engine cranking phase has ended, the PCM cranking relay will now be opened and the BCM cranking relay will now be closed. All of the next automatic ESS cranking events managed in the same Key ON ignition cycle are performed maintaining the BCM cranking relay closed and setting closed the PCM cranking relay. Each time an ESS cranking event occurs which causes the engine to come on again, the PCM cranking relay is opened.

For ATX equipped vehicles, the PCM sends a signal to TCM to indicate it is ready for an ESS event, then TCM responds it is ready for ESS and enters a hydraulic neutral state while in an Auotstop event and stays in hydraulic neutral while Autocranking to avoid vehicle movement during engine cranking.

For MTX equipped vehicles, the PCM will initiate the ESS start event with a short press of the clutch pedal when the MTX is in neutral. The PCM will allow an ESS autostart event to occur while in a drive engaged gear if the clutch pedal travel goes past the interlock position. Otherwise the PCM will trigger an IPC display message to alert the driver to either press the clutch in or shift the transmission into neutral.

Refer to COMPONENT INDEX .

The ABS module incorporates the Electronic Stability Control (ESC) system. On vehicles equipped with Hill Start Assist (HSA), the ABS module also incorporates the HSA strategy.

On vehicles that are not equipped with HSA, there is a brake hold feature designed for the ESS system that should prevent the vehicle from lurching forward during an ESS autostart on downhill grades. The ESC will attempt to hold the brake system pressure when the ESS system has determined that the vehicle is at a stand still on a downhill grade and the ABS module has received a bus message indicating the ESS autostop engine shutdown is in an active state. The system holds brake system pressure until either a bus message is received indicating that the engine is running again or a message indicating that the gas pedal position is greater than 0% from the Accelerator Pedal Position Sensor (APPS). No drive torque balancing is required. Brake system pressure is ramped out quickly as possible when either of those two signals meet the specified values.

Standard HSA and ESS HSA functionality remain unchanged.

On vehicle that are equipped with the HSA function for the ESS system, this functions only when the engine is running as well as the transmission shifter is in a specified gear location and downhill grade criteria is met. The ESS application is designed to shut off the engine as vehicle braking is applied by the driver. To avoid unintentional rollback, the HSA functionality is required while the engine is off and the vehicle is stopped on a shallower grade. The HSA will remain functional through the supply voltage dip experienced during warm engine cranking.

When the vehicle comes to a stand still and the ESS system state changes to indicate that an ESS autostop event is pending, the ESC activates the ESS HSA providing that the ESS HSA grade criteria is met and an adequate amount of brake master cylinder pressure is available. Note that the ESS HSA functionality will have a different HSA activation grade threshold to meet the vehicle application. When the ESS HSA function is active, the ESC will isolate the appropriate amount of brake system pressure needed. If the grade is greater than the ESS HSA grade threshold but less than the standard HSA grade threshold, the ESS HSA functions depending on the vehicle application and specified by the ESC system. The ESC system will:

• Deactivate when the ESS engine states changes to engine running.
• Remain active until the HSA timeout or engine drive off torque balancing values are met.

The ESC communicates the HSA state and the calculated HSA holding pressure over the Controller Area Network-Chassis (CAN-C) network bus. This signal identifies the following states of the HSA system:

• HSA is not active/pending. This indicates that the HSA activation requirements are yet to be determined or the vehicle is not at a stand still.
• Vehicle stand still has been detected and the HSA is not holding braking system pressure.
• A stand still and grade have been detected and the HSA signal is indicating what the minimum braking system pressure required is needed to hold the vehicle on the grade. This signal must compensate for loss of engine creep/idle torque when the engine shuts down. This signal must quickly transition to the required braking system hold pressure after determining vehicle stand still and detection of the grade. This signal must quickly transition directly to the calculated braking system hold pressure if the grade is greater then the ESS HSA calibrated threshold. The signal can differ from the actual pressure that the HSA system is holding. The PCM will compare the brake master cylinder pressure to the signal to ensure that enough brake system pressure is in the brake system to hold the vehicle before an ESS autostop event is performed. If the brake pressure signal is Signal Not Acquired (SNA), all HSA functionality is disabled due to a system fault.
• ESS HSA will not disable when the HSA feature is disabled by the customer using the programmable options menu to turn the HSA system off.

The ABS/ESC module:

• is responsible for reading and reporting the state of the Vehicle Speed Sensor (VSS) as well as the wheel speed Revolution Per Minute (RPM) calculations.
• reports the rolls test bench mode state.
• reports out the current state of the brake pedal position.
• reports out the Yaw rate.
• reports out vehicle longitudinal acceleration and vehicle lateral acceleration readings.

Refer to COMPONENT INDEX .

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.

Refer to COMPONENT INDEX .

During ESS cranking events, both batteries work together to provide a capable starter load. During ESS autostop or autostart events, the two batteries operate independently:

• The larger cranking battery supports the engine cranking events.
• The smaller auxiliary battery supports the vehicles electrical load during ignition ON, engine OFF ESS system events.

Both the primary cranking battery and the auxiliary battery operating parameters are managed by PCM ESS logic and are controlled by the PCR.

If the auxiliary battery is disconnected, the PCM will set a DTC at Key ON. The PCM will then inhibit the ESS system until the DTC is cleared. The PCM will then bus a signal to display a telltale message on the IPC for the driver even if a different display menu is currently being used.

The PCM checks direct battery input which is wired from the auxiliary battery during an ESS autostart event and compares it to two calibrated thresholds within the PCM logic. If the battery input is lower than the first threshold, the PCM will inhibit ESS, such to allow the battery to charge for a calibrated engine run time, and displays a "Battery Charging" message in the ESS IPC menu, in addition to an incrementing a counter, if counter reaches its calibrated threshold, PCM will set a DTC and the PCM will then bus a signal to display a telltale message on the IPC for the driver even if a different display menu is currently being used and inhibit ESS until the DTC is cleared. If the battery input is lower than the second threshold then the PCM will set a DTC for a depleted Auxiliary battery and disable the ESS system. The PCM will then bus a signal to display a telltale message on the IPC for the driver even if a different display menu is currently being used.

Dual Battery Control Relay (DBCR) and Power Control Relay (PCR)

The DBCR is used by the PCM to control the PCR.

The PCR is placed in between the Cranking battery and the Auxiliary battery and is used to isolate the two batteries from each other in order to avoid voltage dips when the starter cranks the engine during an ESS Autostart event.

The larger Cranking battery is responsible for engine cranking. The smaller Auxiliary battery is responsible for managing the vehicles electrical load demand during ESS autostop (engine off).

During ESS cranking events, the PCM commands the PCR to open for a calibratable time to isolate the Auxiliary battery.

The DBCR is OBDII diagnosed for short to ground, short to battery and open circuit.

The PCR is also OBDII diagnosed for stuck open and stuck closed. For a stuck closed PCR, OBDII can determine faults based on voltage difference between Auxiliary battery and Cranking battery. If a stuck closed Diagnostic Trouble Code (DTC) is matured, the Powertrain Control Module (PCM) busses a signal for the IPC to display an ESS message to the driver. For a stuck open PCR, OBDII diagnostics can determine failure on voltage during Key ON Engine ON. If a stuck open DTC is matured, the PCM also busses a signal for the IPC to display an ESS message to the driver.

Refer to COMPONENT INDEX .

The START/STOP Off switch is a driver select feature that permits the driver to inhibit the ESS feature from performing ESS stop and ESS start events. The START/STOP Off switch, which is located on the interface of the ICS switch bank, generates a signal that is transmitted to the BCM. The signal displays the ESS status when the customer disables the START/STOP Off switch. This is primarily used for feedback return to illuminate the START/STOP Off switch Light Emitting Diode (LED). When the ESS system is ON, there is no LED indication shown. When the ESS system is off or inhibited, the LED is constantly illuminated.

The PCM follows OBDII regulations for inhibited ESS to prevent failure in order to determine if the START/STOP Off switch is stuck. The START/STOP Off switch diagnostics will compare the state of two input switches. In the event that there is a disagreement between the states of the two switches, the PCM logic concludes that one of the switches has failed. Because this type of diagnostic cannot determine which switch is failed (and therefore the true state of the START/STOP Off switch press), the PCM assumes that the driver of the vehicle will not be able to inhibit the ESS system which, in turn, the PCM will set the appropriate DTCs. Until a fault has been validated, either switch input is accepted as a request to inhibit, thus not requiring both inputs to be set. The PCM will allow the START/STOP Off switch a calibrated limit of soft fails before the PCM matures those soft fails to hard fails.

Refer to COMPONENT INDEX .

Following an ESS autostart event, the generator will ramp up its duty cycle slowly enough to prevent IPC flickering and allow for acceptable vehicle performance and driveability. The generator duty cycle ramp is managed by the PCM.

This generator has no requirements for voltage regulation on ESS systems.

Refer to COMPONENT INDEX .

The PCM sends activation signals to the IPC requesting that the IPC displays specific ESS system messages. The PCM can send several variations of the same signal to the IPC to provide different messages on the IPC. When required, the IPC will activate the following messages to the driver of the vehicle:

• S&S NOT AVAILABLE-SERVICE BATTERY VEHICLE SHUT OFF
• S&S NOT READY DRIVER SB UNBUCKLED
• S&S NOT AVAILABLE DRIVER NOT DETECTED
• S&S NOT READY DRIVER DOOR OPEN
• S&S RESTART REQUIRED FAULT DETECTED
• S&S NOT AVAILABLE SERVICE BATTERY
• S&S FAIL
• S&S TO RESTART RELEASE PARK BRAKE
• S&S CANNOT AUTOSTART HOOD OPEN
• S&S NOT READY PASSENGER DOOR OPEN
• S&S SHIFT TO PARK
• S&S NOT READY
• S&S RECOVERY FAIL MESSAGE
  NOTE:

  This message is due to a loss of communication

• S&S NOT AVAILABLE ENGINE OFF
• S&S NOT AVAILABLE-MENU
• S&S AUTO STOP ACTIVE
• S&S NOT AVAILABLE-DRIVER SB UNBUCKLED
• S&S NOT AVAILABLE DRIVER DOOR OPEN-MENU
• S&S NOT AVAILABLE PRESS CLUTCH OR SHIFT TO NEUTRAL-MENU
• S&S RESTART REQUIRED
• S&S NOT AVAILABLE BATTERY FAIL
• S&S READY
• S&S NOT AVAILABLE HOOD OPEN
• S&S NOT AVAILABLE ACCELERATOR DEPRESSED
• S&S NOT AVAILABLE BATTERY CHARGING
• S&S NOT AVAILABLE TOW AVAILABLE
• S&S NOT AVAILABLE 4LOW ACTIVE
• S&S NOT AVAILABLE LOW FUEL
• S&S NOT AVAILABLE CABIN COOLING OR HEATING
• S&S NOT AVAILABLE MAX COOLING OR HEATING
• S&S NOT AVAILABLE F DEFROST ACTIVE
• S&S NOT AVAILABLE R DEFROST ACTIVE
• S&S NOT AVAILABLE TURNED STEER WHEEL
• S&S NOT AVAILABLE ENGINE TEMP HIGH
• S&S NOT AVAILABLE ENGINE TEMP LOW
• S&S NOT AVAILABLE DEF RGN
• S&S NOT AVAILABLE TOO STEEP
• S&S NOT AVAILABLE OUTSIDE TEMP
• S&S NOT AVAILABLE ACC ACTIVE
• S&S NOT AVAILABLE BATTERY PROTECTION
• S&S NOT AVAILABLE PRESS CLUTCH OR SHIFT NEUTRAL
• S&S PRESS CLUTCH OR SHIFT NEUTRAL
• S&S NOT AVAILABLE SHIFT TO P

The IPC receives bussed messages requesting ESS chime activation and ESS switch status information from the PCM using the CAN network.

Refer to COMPONENT INDEX .

• The IBS is responsible for measuring the State-of-Charge (SOC). It will also predict voltage and capacity (Ah) for future ESS crank events. The IBS is also responsible for measuring battery temperature and generator voltage currents.
• The IBS temperature sensor is compared to the rationalized Engine Coolant Temperature (ECT) sensor readings on power up. On detection of failure, the IBS battery temperature is then compared against ambient temperature to ensure that the fault is not caused by the use of an engine block heater. Also, provision is made to ensure the use of a battery mat heater will not cause the diagnostic to false fail.

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 Dual Battery Control Relay otherwise known as the Power control relay (PCR) 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 Unstopped	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.

Refer to COMPONENT INDEX .

• This vehicle is equipped with an enhanced starter with increased life brushes, needle bearings, pre-loaded pinion gear spring and other changes to enhance longevity and improve Noise, Vibration, Harshness (NVH).
• This starters power is increased to compensate for brush losses and to increase cranking speed.
• The PCR is required to achieve minimum system voltage drop requirements of critical modules and devices and autostop duration and frequency objectives.

Refer to COMPONENT INDEX .

Every engine start (auto or driver induced) is recorded by increments on a counter. When the count is equal to a calibrated threshold, the ESS autostop event is inhibited until a cool down cycle has been run. The number of allowable ESS start events is a function of the ambient temperature. As the ambient temperature increases, the number of ESS events will decrease. The quick cool down cycle is defined as a calibrated drive period above a calibrated vehicle speed. The slow cool down cycle is defined as the time from the last crank since the inhibit event was recorded.

If the starter is energized by the starter control relay during an Autostart event and the engine does not start within a calibrated time, the starter control relay will be deactivated and an ignition cycle will then be required. If the starter is energized by the starter control relay and run mode is not achieved, the PCM will drop the Low Side Driver (LSD) to the starter control relay and command the BCM to drop the Low Side Driver (LSD). At this point for either scenario, the ESS will be disabled and a DTC will set.

Refer to COMPONENT INDEX .

The TCM determines if the following conditions are met to perform an ESS autostop event:

• The TCM receives a CAN-C bus message from the PCM that indicates that there is an ESS autostop event pending and that the engine itself is ready for the ESS autostop event.
• The TCM receives a Electronic Stability Program (ESP) or an Electronic Stability Control (ESC) derived CAN-C bus message from the ABS module which indicates the vehicles speed threshold over a calibrated frame of time.
• The TCM determines that the transmission is not in (R)  reverse or that the there is not a TCM SNA error. The TCM needs to see that either a forward gear is engaged or that the transmission is in (N)  neutral.
• The TCM determines if there are any DTCs on the transmission which can inhibit the ESS autostop. If a fault is detected, the TCM busses a fault CAN-C bus message back to the PCM. If no fault is detected, the TCM will bus a no fault CAN-C bus message to the PCM.
• The TCM then determines if it can allow the transmission into (P)  park or (N)  neutral.
• The TCM then determines if the PCM CAN-C bus received message indicates that the engine is ready or is not ready for an ESS. A true CAN-C bus message attribute indicates that the CAN-C bus message received from the PCM does indicate that the engine is ready for an ESS event.
• Once the TCM verifies that the CAN-C bus message received from the PCM indicates that the engine is ready for an ESS autostop event, the TCM sends a CAN-C bus message back to the PCM indicating that the transmission is prepared and ready for an ESS autostop event to occur.
• The TCM then holds the "ready for ESS autostop event=True" state during the actual autostop event.
• During the actual ESS autostop event, the TCM indicates that the transmission is in a pseudo drive hydraulic neutral gear known as D6 and sends a CAN-C bus message to the PCM advising that the transmission is in a neutral state. This D6 gear state is also indicative of the transmission being in an open transmission torque path. D6 must be achieved prior to engaging the starter motor in response to a driver start request. The TCM busses a message indicating the drive state of the transmission being open or not open.

The TCM determines if the following conditions are met to perform an ESS autostart event:

• The PCM sends a CAN-C network bussed message to the TCM indicating that there is an active request to start the engine.
• If the transmission equipped in this vehicle is equipped with a Hydraulic Impulse Storage (HIS) solenoid, the HIS is released when a CAN-C network bus message from the PCM indicates that the engine is starting.
• The PCM then starts the engine.
• The TCM then engages the appropriate gear.

TCM reaction to a driver departure condition - The TCM can secure the vehicle by shifting into (P)  park if there is a recognized driver departure. The PCM monitors DPDM conditions that indicate driver departure, and if the PCM determines this to be true, the PCM sends a CAN-C network bus message to the TCM requesting that the TCM shift to (P)  park. At this time, the TCM must place the transmission into the (P)  park position.

Refer to COMPONENT INDEX .

The following conditions must be true for the vehicle to perform an ESS auto stop event:

• An ABS event not present
• Flex fuel learned is true
• ESS related system faults are not present
• Driver seat belt buckled
• Driver door closed
• DPDM indicates seat is occupied
• If the vehicle is quipped with an ATX, any forward transmission gear state must be detected
• If the vehicle is equipped with a MTX, the transmission must be in neutral with the clutch pedal in a released state
• ESS inhibit START/STOP Off switch is not pressed
• Battery state is at an acceptable level
• ECT is within calibrated range
• Ambient temperature is within calibrated range of -23°C (-9°F) to 43°C (109°F)
• Steering wheel inputs are acceptable
• Engine speed is below a calibrated threshold
• Vehicle speed is below a calibrated threshold (APPS indicates that the throttle pedal is not pressed)
• Vehicle latch speed achieved (ESS Autostop is permitted)
• Starter motor engagement frequency has not exceeded the calibrated number of allowable attempts
• Brake booster vacuum level is within calibrated range
• Barometric pressure value is within calibrated range
• Hood not open and no rationality faults present
• Hill grade is below calibrated range and HSA is ready
• Fuel level is within calibrated range
• Master cylinder pressure in allowable range to perform Autostop and HSA
• Engine run time is above a calibrated threshold
• Transfer case status is in acceptable state (not in 4-Low). Reported by the Drivetrain Control Module (DTCM).
• Park maneuver is not detected
• Transmission is ready for ESS operation
• No faults present in the ATX or MTX transmission
• HVAC demand is not present
• Oil temperature is within a calibrated range
• Variable Valve Timing (VVT) is in default position
• Exhaust Gas Recirculation (EGR) is ready (if equipped)
• Multi-air system ready (if equipped)
• Starter diagnostics are not running
• Catalyst light is off

The following conditions allow for engine start:

• No OBDII compliant faults are present or detected
• Hood ajar switches are indicating a closed state.
• No ESS inhibit or ESS disarm conditions are present.
• Starter strategies managed by the PCM indicate that starter operation is allowable.
• RPM readings are below a run threshold calibrated by the PCM.

Certain ESS related system faults and vehicle conditions will inhibit the ESS operation. The following items on this list can be listed due to rationality faults, sensor faults, hardware faults, communication faults or SNA faults:

• Ambient temperature during engine restart
• Catalyst temperature during engine restart
• ECT during engine restart
• Battery temperature during engine restart
• Engine oil temperature during engine restart
• Certain HVAC load demands
• Cam sensor faults; intermittent or otherwise
• Cam/crank rationality; intermittent or otherwise
• APPS faults detected
• Steering Angle Sensor (SAS) faults during engine restart
• Driver door ajar switch fault
• Seat belt circuit fault
• Hood detection fault
• Clutch pedal position faults
• HSA within range to hold the vehicle faults
• Brake booster pressure faults
• Fuel level faults during engine restart
• Torque security faults
• Loss of bus communication during engine restart
• Accelerometer sensor diagnostics
• Starter control. Anything that disables first crank would disable ESS
• Starter relay fault
• Starter relay circuit faults
• Air bag deployment
• DPDM faults
• PCR Stuck Open Fault
• PCR Stuck Closed Fault
• Auxiliary Battery depleted
• Auxiliary Battery disconnected
• Battery SOC below calibrated threshold
• Vehicle altitude is above a calibrated threshold

Refer to COMPONENT INDEX .

The RFH sends FOBIK data over the bus to the Body Control Module (BCM) after a valid key fob is verified at the initial start up of the vehicle when the Start/Stop Button is activated.