Part 2
ENGINE CONTROL COMPONENTSIgnition Switch Position Run (ISP-R)
The ISP-R provides the PCM with a VBAT input signal from the ignition switch, indicating that the ignition is in either the ON or START position. When the operator turns the ignition to the OFF or ACC position, the internal combustion engine immediately ceases to provide power. The PCM coordinates the power down sequence by controlling the VPWR circuit and issuing the correct commands to shut down the electrical system in an orderly fashion. For additional information, refer to the Normal Power Down Sequence in Hybrid Electric Control Software. The PCM maintains power to the TCM through the VPWR until the power down sequence is complete. The TBCM is always powered directly from the low voltage battery which permits wake-up when the vehicle is off. Hybrid Electric Control Software
Ignition Switch Position Run/Start (ISP-RS)
The ISP-RS provides the PCM with a VBAT input signal from the ignition switch, indicating the ignition is in the START position.
Immediate Shut Down (ISDN) 1 and 2
The TCM receives the redundant ISDN1 and ISDN2 signals from the high voltage traction battery. Under normal operating conditions the TCM monitors both ISDN circuits for low voltage battery voltage. If at any time during normal operation the TCM detects voltage drop on both ISDN circuits, the electronically controlled continuously variable transaxle (CVT) immediately stops delivering any torque, reduces operating voltage to under 50 volts, and discharges the high voltage capacitors. This action disables the vehicle until the ignition is cycled OFF and ON. The voltage drop on both ISDN circuits is usually a result of some other concern in the hybrid electric system, and DTCs indicating root cause may be stored in other modules. If the voltage drop is detected on only one of the ISDN circuits, the TCM continues its operation and stores the appropriate DTC. The voltage drop on only one of the ISDN circuits usually indicates an open ISDN circuit.
Inertia Fuel Shut-off (IFS) Switch
The IFS switch is used in conjunction with the electric fuel pump. The purpose of the IFS switch is to shut off the fuel pump if a collision occurs. It consists of an inverted pendulum mass that is retained in a conical cone via a set of linear springs. When a sharp impact occurs, the pendulum shifts out of the conical cone, opens the circuit and shuts off the electric fuel pump. Once the switch is open, it must be manually reset before restarting the vehicle.
Typical Inertia Fuel Shut-off (IFS) Switch:
Intake Air Temperature (IAT) Sensor
The IAT sensor is integrated into the mass air flow (MAF) sensor. It is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases, and the resistance increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.
A thermistor type sensor is considered a passive sensor. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in the total current flow.
Voltage that is dropped across a fixed resistor in series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.
The IAT sensor provides air temperature information to the PCM. The PCM uses the air temperature information as a correction factor in the calculation of fuel and ignition timing.
Integrated Mass Air Flow/Intake Air Temperature (MAF/IAT) Sensor:
Knock Sensor (KS)
The KS is a tuned accelerometer on the engine which converts engine vibration to an electrical signal. The PCM uses this signal to determine the presence of engine knock and to retard spark timing.
Manifold Absolute Pressure (MAP) Sensor
The MAP sensor uses a piezo-resistive silicon sensing element to provide a voltage proportional to the absolute pressure in the intake manifold.
The MAP sensor is part of the EGR system. The PCM uses information from the MAP, TP, MAF, CHT and CKP sensors to determine how much exhaust gas is introduced into the intake manifold.
Manifold Absolute Pressure (MAP) Sensor:
Mass Air Flow (MAF) Sensor
The MAF sensor uses a hot wire sensing element to measure the amount of air entering the engine. Air passing over the hot wire causes it to cool. This hot wire is maintained at 200°C (392°F) above the ambient temperature as measured by a constant cold wire. If the hot wire electronic sensing element must be replaced, then the entire assembly must be replaced. Replacing only the element may change the air flow calibration.
The current required to maintain the temperature of the hot wire is proportional to the volume of air flow. The MAF sensor then outputs an analog voltage signal to the PCM proportional to the intake air mass. The PCM calculates the required fuel injector pulse width in order to provide the desired air/fuel ratio.
The MAF sensor is located between the air cleaner and the throttle body inside the air cleaner assembly.
Integrated Mass Air Flow/Intake Air Temperature (MAF/IAT) Sensor:
Motor Electronics Coolant Temperature (MECT) Sensor
The MECT sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases, and the resistance increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature. A thermistor type sensor is considered a passive sensor. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow. Voltage that is dropped across a fixed resistor in a series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor. The MECT provides motor electronics cooling system temperature information to the PCM. The PCM uses this information for determining when to activate the cooling system fans and indicate over-temperature.
Motor Electronics Coolant Temperature (MECT) Sensor:
Motor Electronics Cooling System (MECS) Pump
The motor electronics cooling system is required to maintain an acceptable temperature for the transaxle and the DC/DC converter. The system temperature is monitored by the motor electronics coolant temperature (MECT) sensor, which is an input to the PCM. The PCM commands the MECS pump using the MECS pump relay. The MECS pump is commanded on whenever the traction battery contactors are closed. The coolant in the system flows in a loop from the MECS pump, to the transaxle, then into the MECS radiator bottom hose port, out of the top hose port of the MECS radiator, into the DC/DC converter, and back into the MECS pump. The cooling system has a degassing system that is connected in parallel between the MECS radiator and the MECS pump. The degassing system bleeds air/gases into the degas reservoir.
Motor Electronics Cooling System (MECS) Pump:
Motor Electronics Coolant Flow:
Motor Shut Down (MSDN)
The PCM keeps the traction motor inverter enabled by continuously toggling the generator motor shut down (GMSDN) output. Typical output frequency varies between 49 and 75 Hz at 50% duty cycle. The PCM also broadcasts a redundant not shutdown message to the TCM over the communication link. When a concern condition is detected, the PCM stops generating this frequency signal and broadcasts a shutdown message to the TCM over the CAN communication link. The TCM then disables the traction motor inverter and sets an appropriate DTC. In the event of GMSDN circuit failure, the PCM still broadcasts a not shutdown message but the hard wire signal frequency is out of expected range. If the circuit becomes open, the vehicle shutdowns and the TCM sets the appropriate DTC.
Throttle Actuator Control (TAC) Motor
The TAC motor is a DC motor controlled by the PCM (requires two wires). The motor housing is integrated into the main housing. An internal spring is used to return the throttle plate to a default position. The default position is typically a throttle angle of 7 to 8 degrees from the hard stop angle. The closed throttle plate hard stop is used to prevent the throttle from binding in the bore. This hard stop setting is not adjustable and is set to result in less airflow than the minimum engine airflow required at idle. For additional information, refer to the Torque Based Electronic Throttle Control (ETC). Description and Operation
Torque Of Generator-AC (TGAC) Signal
The TCM calculates an AC generator torque from an AC current measured by the current sensor which is located inside the transaxle. The TGAC is a 50% duty cycle signal which the TCM sends to the PCM over the TGAC circuit. The TCM also broadcasts a redundant generator torque message to the PCM over the communication link. The typical TGAC signal ranges from 200 Hz to 400 Hz, where 300 Hz is equal to 0 Nm (0 lb ft) of torque, 200 Hz is equal to 250 Nm (185 lb ft) of negative torque, and 400 Hz is equal to 250 Nm (185 lb ft) of positive torque. The PCM uses the generator torque value as an input to the energy management control strategy, the torque monitor strategy, and the regenerative brake torque limits strategy. In the event of TGAC circuit failure the PCM initiates limited operating strategy (LOS) shutdown mode which disables the vehicle. The PCM also stores an appropriate DTC.
Torque Of Motor-AC (TMAC) Signal
The TCM calculates an AC traction motor torque from an AC current measured by the current sensor which is located inside the transaxle. The TMAC is a 50% duty cycle signal which the TCM sends to the PCM using the TMAC circuit. TCM also broadcasts a redundant traction motor torque message to the PCM over the communication link. The typical TMAC signal ranges from 200 Hz to 400 Hz, where 300 Hz is equal to 0 Nm (0 lb ft) of torque, 200 Hz is equal to 250 Nm (185 lb ft) of negative torque, and 400 Hz is equal to 250 Nm (185 lb ft) of positive torque. Positive torque is perceived as vehicle acceleration and negative torque is perceived as braking. The PCM uses the traction motor torque value as an input to the energy management control strategy, the torque monitor strategy, and the regenerative brake torque limits strategy. In the event of TMAC circuit failure the PCM initiates limited operating strategy (LOS) shutdown mode which disables the vehicle. The PCM also stores an appropriate DTC.
Transmission Range (TR) Sensor
Overview
The TR sensor communicates the gear selector position the driver selects to the PCM. The PCM determines a gear mode based on the TR input and the vehicle speed signal. The PCM then broadcasts a gear mode message over the communication link. The TCM uses the gear mode message to engage the transaxle in the gear the driver selected. The other control modules use the gear mode message to control the rear lamps or a brake shift interlock solenoid. The TR sensor is mounted at the base of the gear selector assembly and the sensor shaft is moved by the selector.
Transmission Range (TR) Sensor:
TR Sensor and PCM Interface
The TR sensor is a linear potentiometer device that provides the PCM with a percentage of input voltage proportional to the rotational angle of the sensor shaft. The TR sensor consists of:
- two independent (TR-A1 and TR-A2) signals
- two 5 volt reference (TR-VREF1 and TR-VREF2) lines
- two signal return (TR-RTN1 and TR-RTN2) lines
The TR-A1 signal has a negative voltage slope, meaning the voltage decreases when the sensor angle increases. The typical TR voltage ranges from approximately 4.3 volts in the PARK position to approximately 0.6 volt in the LOW gear position. The TR-A2 signal has a positive voltage slope. Voltages increase as the sensor angle increases. The typical voltage for the TR-A2 is about 1 volt in the PARK position to about 4.4 volts in the LOW gear position.
The TR-VREF circuits are bussed together internal to the TR sensor, and both TR-RTN circuits are bussed together in the TR sensor. One of the TR-VREF and one of the TR-RTN circuits are dedicated signals from the PCM. This design of redundant signals protects against an open circuit condition.
Voltage Versus Angle and Gear Selected Chart
Voltage Versus Angle And Gear Selected Chart:
If the PCM detects a concern in one of TR signal inputs, it uses the other TR signal to determine what gear the driver selects. If the PCM detects one or more TR signals that are invalid, the PCM:
- allows the vehicle to travel in DRIVE position or LOW gear position if the vehicle was driving forward at a significant speed when the concern was detected.
- allows the vehicle to travel in REVERSE gear if the vehicle was driving backwards at a significant speed when the concern was detected.
- broadcasts gear mode - NEUTRAL over the communication link when vehicle speed decreases to 8 km/h (5 mph).
- sets the DTC and illuminates the indicator.
Universal Heated Oxygen Sensor (HO2S)
The universal HO2S, sometimes referred to as a wideband oxygen sensor, uses the typical HO2S combined with a current controller in the PCM to infer an air/fuel ratio relative to the stoichiometric air/fuel ratio. This is accomplished by balancing. the amount of oxygen ions pumped in or out of a measurement chamber within the sensor. The typical HO2S within the universal HO2S is used to detect the oxygen content of the exhaust gas in the measurement chamber. The oxygen content inside the measurement chamber is maintained at the stoichiometric air/fuel ratio by pumping oxygen ions in and out of the measurement chamber. As the exhaust gasses get richer or leaner, the amount of oxygen that must be pumped in or out to maintain a stoichiometric air/fuel ratio in the measurement chamber varies in proportion to the air/fuel ratio. The amount of current required to pump the oxygen ions in or out of the measurement chamber is used to measure the air/fuel ratio. The measured air/fuel ratio is actually the output from the current controller in the PCM and not a signal that comes directly from the sensor.
The universal HO2S also uses a self-contained reference chamber to make sure an oxygen differential is always present. The oxygen for the reference chamber is supplied by pumping small amounts of oxygen ions from the measurement chamber into the reference chamber. The universal HO2S does not need access to outside air.
Part to part variance is compensated for by placing a resistor in the connector. This resistor is used to trim the current measured by the current controller in the PCM.
Embedded with the sensing element is the universal HO2S heater. The heater allows the engine to enter closed loop operation sooner. The heating element heats the sensor to a temperature of 780°C (1,436°F). The VPWR circuit supplies voltage to the heater. The PCM controls the heater on and off by providing the ground to maintain the sensor at the correct temperature for maximum accuracy.