Engine Stop Start System

The Engine Stop Start (ESS) system automatically stops and starts the engine when certain conditions are met to improve fuel economy and lower CO2 emissions.

The ESS system utilizes two starter relays to operate the starter motor. The Body Control Module (BCM) controls one relay with a High Side Driver (HSD). When the relay controlled by the BCM is energized, it provides battery voltage to the Powertrain Control Module (PCM) controlled relay. The PCM controls engine cranking by energizing the second starter relay with a Low Side Driver (LSD). The Starter Motor can be disengaged by de-energizing either relay. Diagnostics are performed on the control circuits of each relay. The PCM also monitors the output from the relays to the starter motor on the ignition crank sense circuit. In addition to the control circuit diagnostics for each relay, the PCM also performs diagnostics on the ignition crank sense circuit as well as detecting if one of the relays is stuck in the closed position.

The primary input for an automatic transmission vehicle to gain an ESS autostop is zero vehicle speed with the brake pedal depressed, while the primary input to the ESS autostarting is the release of the brake pedal. Many secondary inputs determine if it is acceptable to autostop and autostart. A number of devices on the vehicle are added or improved to support the ESS function.

Automatic Transmission 

• New thermal management system for maintaining optimum operating temperature
• Vehicle launch control coordination with engine and brake system
• The Transmission Control Module (TCM) receives pseudo drive neutral gear (D6) requests during ESS events. The D6 neutral gear will be needed if the TCM resets due to deep voltage drops during engine cranking. The ESS system waits for confirmation of the neutral gear engagement from the TCM prior to performing the ESS start event. The confirmation D6 neutral signal broadcasts on the Controller Area Network-Chassis (CAN-C) bus.

Batteries - Vehicle Battery and Cranking Battery  - During cranking, both batteries work together to provide a starter load. During an ESS event, the two batteries work separately:

• The smaller vehicle battery supports the vehicle Ignition off electrical load.
• The Larger cranking battery supports the re-start event.

Body Control Module (BCM) 

Modified BCM for communications and starter control.

Door Ajar Switch 

The driver door ajar switch for stop/start vehicles has two diagnostic resistors installed in the latch assembly circuit. This resistor allows the BCM to detect an open or shorted condition in the circuit.

Dual Battery Control and Power Relay 

Engine 

Lubrication system and wear components to manage increased stop and start frequency.

Engine Mounts 

• Modified based on starter packaging. This may be unique for every engine and vehicle.
• Optimized for Noise, Vibration, and Harshness (NVH) given increased engine stop and start frequency.

Electronic Stability Control (ESC) Module 

• The ESC module is integrated and its logic managed by the Antilock Braking System (ABS) module.
• Provides brake controls using Hill Start Assist (HSA) during autostart and transmission engagement transition to prevent vehicle movement while in an autostop condition during the transition from brake pedal to accelerator pedal. Brakes to be released commensurate with torque request and torque capacity
• Ensure module compatibility with cranking during HSA function (voltage drop, etc.)
• When the ESC system is deactivated (OFF) the Light Emitting Diode (LED) lamp in the button will be illuminated.

Flywheel / Driveplate 

Revised ring gear with chamfered, hardened gear teeth to improve starter pinion engagement and reduced gear tooth wear

Generator 

• Higher output generator to provide greater charging capacity immediately following ESS autostarts.
• No requirement for voltage regulation on ESS enabled vehicles.

Intelligent Battery Sensor (IBS) 

The IBS is responsible for measuring the state-of-charge. It will also predict voltage and capacity (ah) for future crank events. The IBS is also responsible for measuring battery temperature and alternator voltage current. This information is provided over the Local Interior Network (LIN) data bus to the BCM as a State of Charge (SOC) message signal.

The IBS is an electrical shunt with a microprocessor that is mounted in-line with the negative battery cable. The IBS monitors the current flow and voltage. The IBS also has a built in thermistor that calculates the battery temperature. The microprocessor uses this data to calculate battery State of Charge (SOC), battery internal resistance, charge received, charge delivered, and time in service. This information is reported through a Local Interface Network (LIN) data bus circuit to the BCM. The BCM broadcasts the information to the Powertrain Control Module (PCM) over the CAN-C BUS.

Instrument Panel Cluster (IPC) 

Revised instrument cluster with stop-start specific graphics and IPC messaging.

Hood Switch 

The hood ajar status is monitored using two switches for the ESS system equipped vehicles. Hood ajar switch 1 is integrated into the hood latch and is hardwired to the BCM. The signal is sent to the PCM over the CAN bus. Hood ajar switch 2 is hardwired to the PCM. If the PCM detects that either switch is in the open position or is faulted for any reason, the ESS feature will be disabled during the current ignition cycle.

Heating, Ventilation, Air Conditioning (HVAC) Control Module 

• Added control features to provide interior climate management.
• Fan speed control adjusted during an ESS autostop.
• ESS autostop inhibit and ESS autostart request based on combination of interior temperature, sun loading and variation from temperature set point and/or ambient temperature. This can impact some ESS events or reduce autostop duration.

Powertrain Control Module (PCM) 

• Circuit board population for added inputs and outputs.
• ESS coordinator added to manage all autostop and autostart activity.
• Impact on torque, security, On Board Diagnostics (OBD) and end of line diagnostics.

Power Control Relay (PCR) 

When in ESS mode, and an Auto Start crank event is initiated, the PCR is temporarily energized which opens the relay, breaking the connection and allowing the dual batteries to work independently. When this occurs, the cranking battery is used to crank and start the engine. The auxiliary battery, which is now solely connected to the Power Distribution Center (PDC) and is not affected by cranking, can maintain full battery voltage to the rest of the vehicle modules and subsystems.

ESC Vacuum Sensor 

Switch located in the vacuum hose connector to initiate ESS autostart in case of low vacuum.

Radio 

Added ESS specific messaging and menu selections.

Integrated Center Stack (ICS) 

Added ESS specific messaging and menu selections.

Starter 

• Enhanced starter with increased life brushes, needle bearings, pre-loaded pinion gear spring and other changes to enhance longevity and improve NVH
• Starter power increased to compensate for brush losses and to increase cranking speed
• In-rush current reduction (ICR) device is required to achieve minimum system voltage drop requirements of critical modules and devices and autostop duration and frequency objectives. It is located on a bracket attached to the lower front of the engine, below the Air Conditioning (A/C) compressor.

Engine Stop Start (ESS) Switch 

• New hard switch located on the ICS switch bank.
• When the Stop/Start system is deactivated (OFF) the LED light in the button will be illuminated.

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 3 systems must perform within specifications. When attempting to diagnose any of these systems, it is important that you keep their interdependency in mind.

The diagnostic procedures used in each of these tests include the most basic conventional diagnostic methods, to the more sophisticated OBD built into the PCM. Use of an induction-type milliampere ammeter, volt/ohmmeter, battery charger, carbon pile rheostat (load tester), and 12-volt test lamp may be required.

Certain starting system components are monitored by the PCM and may produce a Diagnostic Trouble Code (DTC).