Engine Control Components
ENGINE CONTROL COMPONENTSAccelerator Pedal Position (APP) Sensor
There are two pedal position signals in the sensor. Both signals, APP and APP2, have a positive slope (increasing angle, increasing voltage), but are offset and increase at different rates. The two pedal position signals make sure the powertrain control module (PCM) receives a correct input even if one signal has a concern. The PCM determines if a signal is incorrect by calculating where it should be, inferred from the other signals. If a concern is present with one of the circuits the other input is used. There are two reference voltage circuits, two signal return circuits, and two signal circuits (a total of six circuits and pins) between the PCM and the APP sensor assembly. The pedal position signal is converted to pedal travel degrees (rotary angle) by the PCM. The software then converts these degrees to counts, which is the input to the torque based strategy. For additional information, refer to Torque-Based Electronic Throttle Control (ETC).
Brake Pedal Position (BPP) Switch
The BPP switch is a normally open switch that, when closed, sends a signal to the PCM when the brake pedal is applied. The PCM strategy uses this signal input to aid the PCM in determining the correct function and operation of the vehicle speed control, the electronic throttle control (ETC), and the transaxle and regenerative braking systems. The BPP switch is hardwired to the PCM and supplies positive battery voltage (+12 volts) when the brake pedal is applied. When the brake pedal is released, the BPP switch opens and no battery voltage input is sent to the PCM.
Brake Pressure Switch
The brake pressure switch used for vehicle speed control deactivation is a normally closed switch, which supplies positive battery voltage (+12 volts) to the PCM when the brake pedal is released. When the brake pedal is applied, the normally closed switch opens and power is removed from the brake pressure switch circuit to the PCM.
The normally closed brake pressure switch, along with the normally open BPP switch, is used by the PCM strategy for a brake pedal rationality test. The PCM strategy looks for each switch to change states when the brake pedal is applied and released. If a failure occurs in one or both of the brake pedal inputs a diagnostic trouble code is set and the PCM misfire on board diagnostic (OBD) monitor is disabled.
Camshaft Position (CMP) Sensor
The CMP sensor is a Hall-effect sensor that detects the position of the camshaft. The CMP sensor identifies when piston number 1 is on its compression stroke. A signal is then sent to the PCM and used for synchronizing the sequential firing of the fuel injectors. The PCM also uses the CMP signal to select the correct ignition coil to fire.
Canister Vent (CV) Solenoid
During the evaporative emissions (EVAP) leak check monitor, the CV solenoid seals the EVAP canister from the atmospheric pressure. This allows the EVAP canister purge valve to obtain the target vacuum in the fuel tank during the EVAP leak check monitor.
Coil On Plug (COP)
The COPs are part of the distributorless ignition system. They are the source of the high voltage which is used to generate the spark by the spark plug. The hybrid vehicle uses four COPs, one for each cylinder. The COPs are mounted directly onto the spark plugs. The function of the COP is to convert low voltage into high voltage in excess of 40,000 volts.
The COP consists of primary and secondary windings. The primary winding is energized by the IGN START/RUN circuit. The PCM coil driver circuit is connected to the primary winding as well. The secondary winding is connected to the spark plug. The current flowing through the primary winding generates the magnetic field across both windings. The PCM activates the coil driver circuit by opening it. The instant the circuit opens the magnetic field collapses, inducing current flow in the secondary winding.
The COP has three different modes of operation: engine crank, engine running, and CMP failure mode effects management (FMEM).
Crankshaft Position (CKP) Sensor
The CKP sensor is a magnetic transducer mounted on the engine block adjacent to a pulse wheel located on the crankshaft. By monitoring the crankshaft mounted pulse wheel, the CKP is the primary sensor for ignition information to the PCM. The pulse wheel has a total of 35 teeth spaced 10 degrees apart with one empty space for a missing tooth. By monitoring the pulse wheel, the CKP sensor signal indicates the crankshaft position and speed information to the PCM. By monitoring the missing tooth, the CKP sensor is also able to identify piston travel in order to synchronize the ignition system and provide a way of tracking the angular position of the crankshaft relative to a fixed reference. The PCM also uses the CKP signal to determine if a misfire has occurred by measuring rapid decelerations between pulse wheel teeth.
Cylinder Head Temperature (CHT) Sensor
The CHT sensor is a thermistor device in which the 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.
Thermistor type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so varying the resistance of the passive sensor causes a variation in total current flow.
The CHT sensor is installed in the aluminum cylinder head and measures the metal temperature. The CHT sensor provides complete engine temperature information and can be used to infer coolant temperature. If the CHT sensor conveys an overheating condition to the PCM, the PCM then initiates a fail-safe cooling strategy based on information from the CHT sensor. A cooling system failure such as low coolant or coolant loss could cause an overheating condition. As a result, damage to major engine components could occur. Using both the CHT sensor and fail-safe cooling strategy, the PCM prevents damage by allowing air cooling of the engine and limp home capability. For additional information, refer to Powertrain Control Software Fail-Safe Cooling Strategy.
Electric Exhaust Recirculation Valve (EEGR) Valve
The EEGR valve is a water-cooled motor/valve assembly. The motor is commanded to move in 52 discrete steps as it acts directly on the EEGR valve. The position of the valve determines the rate of EGR. The built-in spring works to close the valve against the motor opening force.
Electronic Throttle Body (ETB) Throttle Position Sensor
The ETB throttle position sensor has two signal circuits in the sensor for redundancy. The redundant ETB throttle position signals are required for increased monitoring. The first ETB throttle position sensor signal (TP1) has a negative slope (increasing angle, decreasing voltage) and the second signal (TP2) has a positive slope (increasing angle, increasing voltage). The two ETB throttle position sensor signals make sure the PCM receives a correct input even if one signal has a concern. There is one reference voltage circuit and one signal return circuit for the sensor. The reference voltage circuit and the signal return circuit is shared with the reference voltage circuits and signal return circuits used by the APP sensor. For additional information, refer to the description of the Torque-Based Electronic Throttle Control (ETC).
Evaporative Emission (EVAP) Canister Purge Valve
The EVAP canister purge valve is part of the enhanced EVAP system that is controlled by the PCM. This valve controls the flow of vapors (purging) from the EVAP canister to the intake manifold during various engine operating modes. The EVAP canister purge valve is a normally closed valve. The EVAP canister purge valve controls the flow of vapors electronically by way of a solenoid, eliminating the need for an electronic vacuum regulator and vacuum diaphragm. The PCM outputs a duty cycle between 0% and 100% to control the EVAP canister purge valve.
Fan Control
The PCM monitors certain parameters (such as engine coolant temperature, vehicle speed, A/C on/off status, A/C pressure) to determine engine cooling fan needs.
The PCM controls the fan speed and operation using a duty cycle output on the fan control variable (FCV) circuit. The fan controller (located at or integral to the engine cooling fan assembly) receives the FCV command and operates the cooling fan at the speed requested (by varying the power applied to the fan motor).
Fuel Injectors
NOTICE: Do not apply battery positive (B+) voltage directly to the fuel injector electrical connector terminals. The solenoids may be damaged internally in a matter of seconds.
The fuel injector is a solenoid-operated valve that meters fuel flow to the engine. The fuel injector is opened and closed a constant number of times per crankshaft revolution. The amount of fuel is controlled by the length of time the fuel injector is held open.
The fuel injector is normally closed, and is operated by a 12-volt source from the fuel injector relay. The ground signal is controlled by the PCM.
The injector is the deposit resistant injector (DRI) type and does not have to be cleaned. Install a new fuel injector if the flow is checked and found to be out of specification.
Fuel Pump (FP) Module
The FP module is a device that contains the fuel pump and sender assembly. The fuel pump is located inside the FP module and supplies fuel through the FP module manifold to the engine and FP module jet pump. The jet pump continuously refills the reservoir with fuel, and a check valve located in the manifold outlet maintains system pressure when the fuel pump is not energized. A flapper valve located in the bottom of the reservoir allows fuel to enter the reservoir and prime the fuel pump during the initial fill.
Fuel Tank Pressure (FTP) Sensor
The FTP sensor is used to measure the fuel tank pressure.
Fuel Vapor Vent Valve
The fuel vapor vent valve is a PCM-controlled solenoid that isolates the fuel tank from the rest of the EVAP system. The fuel vapor vent valve is a normally open valve allowing the flow of vapors from the fuel tank to the electronic EVAP canister purge valve and the EVAP canister. The PCM controls the fuel vapor vent valve on/off cycle whenever it is desired to isolate the fuel tank from the rest of the EVAP system.
Heated Oxygen Sensor (HO2S)
The HO2S detects the presence of oxygen in the exhaust and produces a variable voltage according to the amount of oxygen detected. A high concentration of oxygen (lean air/fuel ratio) in the exhaust produces a voltage signal less than 0.4 volt. A low concentration of oxygen (rich air/fuel ratio) produces a voltage signal greater than 0.6 volt. The HO2S provides feedback to the PCM indicating air/fuel ratio in order to achieve a near stoichiometric air/fuel ratio of 14.7:1 during closed loop engine operation. The HO2S generates a voltage between 0.0 and 1.1 volts.
Embedded with the sensing element is the HO2S heater. The heating element heats the sensor to a temperature of 800°C (1,472°F). At approximately 300°C (572°F) the engine can enter closed loop operation. The VPWR circuit supplies voltage to the heater. The PCM turns the heater on by providing the ground when the correct conditions occur. The heater allows the engine to enter closed loop operation sooner. The use of this heater requires the HO2S heater control to be duty cycled, to prevent damage to the heater.
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.
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.
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.
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.
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).
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 on the transmission assembly and the sensor shaft is moved by the selector shaft.
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 signals (TR-A1 and TR-A2)
- two 5 volt reference lines (TR-VREF1 and TR-VREF2)
- two signal return lines (TR-RTN1 and TR-RTN2)
The TR-A1 signal has a positive voltage slope, meaning the voltage increases when the sensor angle increases. The typical TR voltage ranges from approximately 0.7 volt in the PARK position to approximately 3.8 volts in the LOW gear position. The TR-A2 signal has a negative voltage slope. Voltage decreases as the sensor angle increases. The typical voltage for the TR-A2 is approximately 4.3 volts in the PARK position to approximately 1.2 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 internal to 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.
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 the DRIVE 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 malfunction indicator lamp (MIL).
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 into 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 into 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 into 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.
Variable Voltage Controller
The variable voltage controller is located within the transaxle. The variable voltage controller is a bi-directional voltage boost converter that couples the high voltage traction battery to the transaxle's generator motor and traction motor. The variable voltage controller steps up voltage output to maximize motor and generator efficiency. If there is a concern, the transaxle control module (TCM) will bypass the variable voltage controller and set a diagnostic trouble code (DTC).