Power Valve
The power valve is installed in intake manifold collector and is used to control the suction passage of the variable induction air control system. It is set in the fully closed or fully opened position by the power valve actuator operated by the vacuum stored in the surge tank. The vacuum in the surge tank is controlled by the VIAS control solenoid valve.
VIAS Control Solenoid Valve
The VIAS control solenoid valve cuts the intake manifold vacuum signal for power valve control. It responds to ON/OFF signals from the ECM. When the solenoid is off, the vacuum signal from the intake manifold is cut. When the ECM sends an ON signal the coil pulls the plunger downward and feeds the vacuum signal to the power valve actuator.
COMPUTERIZED ENGINE CONTROLS
ECM compares each input signal to the appropriate parameter programmed in ECM and adjusts output voltage signals accordingly. This allows optimum vehicle performance under various conditions. Battery voltage to ECM is supplied by ECCS relay. ECCS relay has a self shut-off feature that cuts power to ECM a few seconds after ignition is turned off.
ENGINE CONTROL MODULE
The Engine Control Module (ECM) consists of a microcomputer, connectors and wiring for voltage signal input/output and power supply. The unit is not serviceable and should not be opened. The ECM contains memory and logic circuits, enabling it to interpret sensor inputs and control various engine systems. To locate ECM, see ECM LOCATIONS table.
| Application | Location |
|---|---|
| All Models | Behind Glove Box |
ECM LOCATIONS
Note. Components are grouped into 2 categories. The first category is INPUT DEVICES , which are components that control or produce voltage signals monitored by the ECM. The second category is OUTPUT SIGNALS , which are components controlled by the ECM.
INPUT DEVICES
Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. For specific inputs, see ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Available input signals include
Absolute Pressure Sensor
The Absolute Pressure (AP) sensor detects ambient barometric pressure and intake manifold pressure and sends a voltage signal to the ECM. Voltage from the sensor increases as pressure increases.
A/C Switch
Informs ECM when A/C system is on. ECM responds by increasing idle speed to improve idling and reduce emissions. ECM will open the A/C clutch relay to disengage A/C clutch during wide open throttle, during engine cranking, high engine speeds, when engine coolant temperature is high, when operating power steering during low engine speed or low vehicle speed and when engine speed is excessively low.
Accelerator Pedal Position (APP) Sensor
The Accelerator Pedal Position (APP) sensor is installed on the upper end of the accelerator pedal assembly. The sensor detects the accelerator position and sends a signal to the ECM.
The APP sensor has 2 sensors. These sensors are a kind of potentiometers which transform the accelerator pedal position into output voltage and emit the voltage signal to the ECM. In addition, these sensors detect the opening and closing speed of the accelerator pedal and feed the voltage signals to the ECM. The ECM judges the current opening angle of the accelerator pedal from these signals and controls the throttle control motor based on these signals.
Idle position of the accelerator pedal is determined by the ECM receiving the signal from the APP sensor. The ECM uses this signal for the engine operation such as fuel cut.
Battery Voltage Compensation
ECM monitors battery voltage to control ignition timing, injector pulse width and idle air control.
Camshaft Position Sensor
The camshaft position sensor (PHASE) senses the protrusion of exhaust camshaft sprocket to identify a particular cylinder. The crankshaft position sensor (POS) senses the piston position. When the crankshaft position sensor (POS) system becomes inoperative, the camshaft position sensor (PHASE) provides various controls of engine parts instead, utilizing timing of cylinder identification signals. The sensor consists of a permanent magnet and Hall IC. When engine is running, the high and low parts of the teeth cause the gap with the sensor to change. The changing gap causes the magnetic field near the sensor to change. Due to the changing magnetic field, the voltage from the sensor changes.
Closed Throttle Position Switch
Closed TP switch is part of the TP sensor. Switch is closed at idle and open during off-idle throttle position. ECM only uses this signal to open or close EVAP canister purge control valve when throttle position sensor is malfunctioning. Switch also has a full throttle position used only for A/T control.
Crankshaft Position Sensor
The crankshaft position sensor (POS) is located on the oil pan facing the gear teeth (cogs) of the signal plate. It detects the fluctuation of the engine revolution. The sensor consists of a permanent magnet and Hall IC. When the engine is running, the high and low parts of the teeth cause the gap with sensor change. The changing gap causes the magnetic field near the sensor to change. Due to the changing magnetic field, the voltage from the sensor changes. The ECM receives the voltage signal and detects the fluctuation of the engine revolution.
Engine Coolant Temperature Sensor
The engine coolant temperature sensor is used to detect the engine coolant temperature. The sensor modifies a voltage signal form the ECM. The modified signal returns to the ECM as the engine coolant temperature input. The sensor uses a thermistor which is sensitive to the change in temperature. The electrical resistance of the thermistor decreases as temperature increases. ECM uses this information for controlling air/fuel mixture, ignition timing, idle speed control and other functions.
Fuel Level Sensor
The fuel level sensor is mounted in the fuel level sensor unit. The sensor detects a fuel level in the fuel tank and transmits a signal to the ECM. It consists of two parts, one is mechanical float and the other side is variable resistor. Fuel level sensor output voltage changes depending on the movement of the fuel mechanical float.
Fuel Tank Temperature Sensor
Fuel Tank Temperature (FTT) sensor is a thermistor located in fuel tank. This sensor modifies a voltage signal from ECM. Resistance decreases as temperature increases. This sensor is used for on-board diagnosis only and not for engine control.
Heated Oxygen Sensor
Sensor monitors the amount of oxygen in the exhaust gas. The heater portion of this sensor quickly brings sensor to operating temperature.
On all models, front HO2S provides a voltage signal which is used by ECM to obtain optimum air/fuel mixture. HO2S returns a sweeping return signal which varies between.25 and.75 volt. A rich exhaust gas mixture causes high sensor voltage (0.6-1.0 volt). A lean exhaust gas mixture causes low sensor voltage (0.1-0.3 volt). The ECM monitors signal from sensor and adjusts the injector pulse width accordingly.
Rear HO2S is used to monitor catalyst efficiency. If switching characteristics of front HO2S are shifted, air/fuel ratio is controlled by rear HO2S input. Under normal conditions, rear HO2S is not used for engine control.
Ignition Switch
ECM detects when ignition switch is in ON or START position. When ECM receives a voltage signal for START position, it will actuate injectors and initiate ignition timing sequence and other functions.
Intake Air Temperature Sensor
The Intake Air Temperature (IAT) sensor is located in the air cleaner duct. Sensor monitors temperature of incoming air. Sensor is a thermistor that increases (cold) or decreases (hot) its resistance in response to temperature changes.
Intake Valve Timing Control Position Sensor
Intake Valve Timing Control (IVTC) position sensor is located at rear of left cylinder head. This sensor detects intake valve position generated by a cutout portion of camshaft and sends it to ECM. This sensor is not used for engine control. It is only used for on-board diagnosis of the IVTC system. (Scheme 1)
Scheme 1
Knock Sensor
The knock sensor is attached to the cylinder block. It senses engine knocking using a piezoelectric element. A knocking vibration from the cylinder block is sensed as vibrational pressure. This pressure is converted into a voltage signal and sent to the ECM.
Mass Airflow Sensor
The mass air flow sensor is placed in the stream of intake air. It measures the intake flow rate by measuring a part of the entire intake flow. It consists of a hot film that is supplied with electric current from the ECM. The temperature of the hot film is controlled by the ECM a certain amount. The heat generated by the hot film is reduced as the intake air flows around it. The more air, the greater the heat loss. Therefore, the ECM must supply more electric current to maintain the temperature of the hot film as air flow increases. The ECM detects the air flow by means of this current change. (Scheme 2)
Scheme 2
Neutral Switch (M/T Models)
Switch is located on manual transmission. Switch notifies ECM when transmission is in Neutral. Information is used to calculate required changes in idle speed, ignition timing and injector operation.
Park/Neutral Position Switch (A/T Models)
Switch is located on transmission/transaxle. Switch notifies ECM when transmission/transaxle is in Park or Neutral. Primary use is to prevent starting the vehicle in Drive. This signal also is used by ECM to calculate required changes in idle speed, ignition timing and injector operation.
Power Steering Pressure Switch
Switch is attached to the power steering high pressure line. Switch monitors the power steering load and sends signal to the ECM. When power steering pressure exceeds a predetermined amount, ECM increases idle speed to compensate for extra load on engine.
Radiator Coolant Temperature Sensor (Q45)
The radiator coolant temperature sensor is installed on the radiator lower tank and is used to detect the radiator coolant temperature. The sensor modifies a voltage signal from the ECM and returns the modified signal to the ECM as the radiator coolant temperature input. The sensor uses a thermistor which is sensitive to the change in temperature. The electrical resistance of the thermistor decreases as temperature increases. The ECM uses this signal to control the cooling fan speed control solenoid valve.
Throttle Position Sensor (TP) Sensor
Electric Throttle Control Actuator consists of throttle control motor, Accelerator Pedal Position (APP) sensor, Throttle Position (TP) sensor, etc. The TP sensor responds to the throttle valve movement. The TP sensor has the 2 sensors. These sensors are a kind of potentiometers which transform the throttle valve position into output voltage and emit the voltage signal to the ECM. In addition, these sensors detect the opening and closing speed of the throttle valve and feed the voltage signals to the ECM. The ECM judges the current opening angle of the throttle valve from these signals and the ECM controls the throttle control motor to make the throttle valve opening angle properly in response to driving condition.
Vehicle Speed Signal
Vehicle speed signal is sent to ECM through the Controller Area Network (CAN).
OUTPUT SIGNALS
Vehicles are equipped with different combinations of ECM-controlled components. Not all components listed below are used on every vehicle. For theory and operation on each output component, refer to the indicated system.
A/C Clutch
See A/C CLUTCH under MISCELLANEOUS CONTROLS.
Cooling Fan Relay
See appropriate COOLING FAN article under MISCELLANEOUS CONTROLS.
Electric Throttle Control Actuator
Electric throttle control actuator consists of throttle control motor, Accelerator Pedal Position (APP) sensor, throttle position sensor, etc. The throttle control motor is operated by the ECM and it opens and closes the throttle valve. APP sensor detects the accelerator pedal position, the opening and closing speed of the accelerator pedal and feeds the voltage signals to the ECM. The ECM judges the current opening angle of the accelerator pedal from these signals and controls the throttle control motor based on these signals. The throttle position sensor detects the throttle valve position and the opening and closing speed of the throttle valve and feeds the voltage signals to the ECM. The ECM judges the current opening angle of the throttle valve from these signals and the ECM controls the throttle control motor to make the throttle valve opening angle properly in response to driving condition.
Evaporative Emission Control System
See EVAPORATIVE EMISSION CONTROL (EVAP) SYSTEM under EMISSION SYSTEMS.
Fuel Injector
See FUEL CONTROL under FUEL SYSTEM.
Fuel Pump Control Module (Q45)
See FUEL DELIVERY under FUEL SYSTEM.
Fuel Pump Relay
See FUEL DELIVERY under FUEL SYSTEM.
Idle Speed Control
See IDLE SPEED under FUEL SYSTEM.
Ignition Timing Control
See IGNITION TIMING CONTROL SYSTEM under IGNITION SYSTEM.
Transmission Control Module
See TRANSMISSION/TRANSAXLE CONTROLS under MISCELLANEOUS CONTROLS.
Fuel Pump (FX35, FX45, I35 & QX4)
The ECM activates the fuel pump for several seconds after the ignition switch is turned on to improve engine startability. If the ECM receives a 120° signal from the camshaft position sensor (PHASE - on FX35, FX45 & I35) (REF - on QX4), it knows that the engine is rotating, and causes the pump to operate. If the 120° signal is not received when the ignition switch is on, the engine stalls. The ECM stops pump operation and prevents battery discharging, thereby improving safety. The ECM does not directly drive the fuel pump. It controls the ON/OFF fuel pump relay, which in turn controls the fuel pump.
Fuel Pump (G35 & Q45)
The electric in-tank fuel pump is turned on by the ECM. Fuel pump is activated when ECM supplies the ground signal for the fuel pump relay. Fuel pump will be energized by the ECM for about 5 seconds when ignition is first turned on. When ECM receives signal from camshaft position sensor (on G35) or crankshaft position sensor (on Q45), fuel pump is energized continuously. Fuel pump will be de-energized about one second after engine stops.
Fuel Pump (M45)
The ECM activates the fuel pump for several seconds after the ignition switch is turned on to improve engine startability. If the ECM receives a 10° signal from the crankshaft position sensor (POS), it knows that the engine is rotating, and causes the pump to operate. If the 10° signal is not received when the ignition switch is ON, the engine stalls. The ECM stops pump operation and prevents battery discharging, thereby improving safety. The ECM does not directly drive the fuel pump. It controls the ON/OFF fuel pump relay, which in turn controls the fuel pump.
Fuel Pump Control Module (M45 & Q45)
When ignition is turned on and engine is cranking or running, fuel pump relay is activated. Battery voltage is directed from the fuel pump relay to Fuel Pump Control Module (FPCM) and fuel pump. The FPCM adjusts the voltage supplied to fuel pump according to engine conditions. FPCM supplies battery voltage to the fuel pump under the following conditions
- During engine cranking.
- When engine coolant temperature is less than 50°F (10°C).
- Engine is running under heavy load and high speed conditions.
Under conditions other than those listed, FPCM limits fuel pump voltage to about 8 volts.
Fuel pump receives battery voltage through a fused circuit from ignition switch. Ground circuit for fuel pump relay is provided through ECM. When fuel pump relay is activated, battery voltage is directed from fuel pump relay to Fuel Pump Control Module (FPCM) and then fuel pump.
Fuel Pressure Regulator
Fuel is delivered to the fuel rail from the in-tank electric fuel pump. Fuel pressure at the fuel rail is regulated by the fuel pressure regulator located in the fuel return line between the fuel rail and the fuel tank. The pressure regulator is a sealed unit divided into 2 chambers (fuel and spring) by a diaphragm. The fuel chamber receives fuel through the inlet side from the injector fuel rail. A vacuum-operated diaphragm inside the regulator maintains fuel pressure at a specific range, taking into consideration changes in engine load.
Feedback System
ECM calculates injection pulse width by processing input signals from ECT, HO2S, TP, MAF and other sensors. After receiving signals from sensors detecting engine conditions, ECM can adjust air/fuel ratio to optimally control exhaust emissions and engine performance.
Fuel injection system incorporates mixture ratio feedback. It is designed to maintain a precise mixture ratio. Through input signals from the front and rear Heated Oxygen Sensors (HO2S), ECM continuously monitors itself to stay within an acceptable emissions output range. However, this feedback system can be overridden and will operate in open loop when one or more of the following conditions exist
- Acceleration or deceleration.
- Starting.
- Warm-up.
- High-speed and heavy load conditions.
- High engine coolant temperature.
- Malfunction of front HO2S or circuit
- Front HO2S cold.
Mixture Ratio Self-Learning Control
The mixture ratio feedback control system monitors the mixture ratio signal transmitted from front HO2S. This feedback signal is then sent to the ECM. The ECM controls the basic mixture ratio as close to the theoretical mixture ratio as possible. However, the basic mixture ratio is not necessarily controlled as originally designed. Both manufacturing differences (i.e., mass air flow sensor hot film) and characteristic changes during operation (i.e., injector clogging) directly affect mixture ratio. Accordingly, the difference between the basic and theoretical mixture ratios is monitored in this system. This is then computed in terms of "injection pulse duration" to automatically compensate for the difference between the 2 ratios.
"Fuel trim" refers to the feedback compensation value compared against the basic injection duration. Fuel trim includes short term fuel trim and long term fuel trim. "Short term fuel trim" is the short-term fuel compensation used to maintain the mixture ratio at its theoretical value. The signal from front HO2S indicates whether the mixture ratio is RICH or LEAN compared to the theoretical value. The signal then triggers a reduction in fuel volume if the mixture ratio is rich and an increase in fuel volume if it is lean. "Long term fuel trim" is overall fuel compensation carried out long-term to compensate for continual deviation of the short term fuel trim from the central value. Such deviation will occur due to individual engine differences, wear over time and changes in the usage environment.
The fuel injector is a small elaborate solenoid valve. The ECM sends a pulse duration signal to the injector, which in turn opens to high pressure fuel supplied by the fuel pump.
The ECM controls the engine idle speed to a specified level through the fine adjustment of the air, which is let into the intake manifold, by operating the electric throttle control actuator. The operating of the throttle valve is varied to allow for optimum control of the engine idling speed. The crankshaft position sensor (POS) detects the actual engine speed and sends a signal to the ECM.
The ECM controls the electric throttle control actuator so that the engine speed coincides with the target value memorized in the ECM. The target engine speed is the lowest speed at which the engine can operate steadily. The optimum value stored in the ECM is determined by taking into consideration various engine conditions, such as during warming up, deceleration and engine load (air conditioner, power steering and cooling fan operation, etc.).
ELECTRONIC IGNITION SYSTEM
Electronic (direct) ignition system uses one coil per cylinder. Individual coils are plugged directly onto spark plugs. ECM receives information such as injection pulse width and Camshaft Position (CMP) sensor signal. Using this information, ECM sends signals to the power transistor (integral with ignition coil).
IGNITION TIMING CONTROL SYSTEM
Ignition timing is controlled by the ECM according to engine operating conditions. Optimum ignition timing for various driving conditions is programmed into the ECM. ECM receives and processes electrical signals from various sensors to determine present driving conditions. ECM will then select optimum timing signal for the present conditions and send voltage signal to control timing advance and retard operation.
Ignition Timing Retard
See KNOCK SENSOR (KS) under INPUT DEVICES under COMPUTERIZED ENGINE CONTROLS.
The evaporative emission system is used to reduce hydrocarbons emitted into the atmosphere from the fuel system. This reduction of hydrocarbons is accomplished by activated charcoals in the EVAP canister. The fuel vapor in the sealed fuel tank is led into the EVAP canister which contains activated carbon and the vapor is stored there when the engine is not operating or when refueling to the fuel tank. The vapor in the EVAP canister is purged by the air through the purge line to the intake manifold when the engine is operating. EVAP canister purge volume control solenoid valve is controlled by ECM. When the engine operates, the flow rate of vapor controlled by EVAP canister purge volume control solenoid valve is proportionally regulated as the air flow increases. EVAP canister purge volume control solenoid valve also shuts off the vapor purge line during decelerating and idling. (Scheme 3)
Scheme 3
Evaporative Canister
Filled with activated charcoal, canister stores fuel tank vapors to be burned via air induction. Locating EVAP canister for FX35 and FX45 (Scheme 4), for G35 (Scheme 5), for I35 (Scheme 6), for M45 and Q45 (Scheme 7), for QX4 (Scheme 8)
Scheme 4
Scheme 5
Scheme 6
Scheme 7
Scheme 8
EVAP Canister Purge Volume Control Valve
This system controls flow rate of fuel vapor from the EVAP canister. The opening of the vapor by-pass passage in the EVAP canister purge volume control solenoid valve changes to control the flow rate. The EVAP canister purge volume control solenoid valve repeats ON/OFF operation according to the signal sent from the ECM. The opening of the valve varies for optimum engine control. The optimum value stored in the ECM is determined by considering various engine conditions. When the engine is operating, the flow rate of fuel vapor from the EVAP canister is regulated as the air flow changes.
EVAP Canister Vent Control Valve
The EVAP canister vent control valve is located on the EVAP canister and is used to seal the canister vent. This solenoid valve responds to signals from the ECM. When the ECM sends an ON signal, the coil in the solenoid valve is energized. A plunger will then move to seal the canister vent. The ability to seal the vent is necessary for the on board diagnosis of other evaporative emission control system components. This solenoid valve is used only for diagnosis and usually remains opened. When the vent is closed, under normal purge conditions, the evaporative emission control system is depressurized and allows "EVAP Control System" diagnosis.
Vacuum Cut Valve & Vacuum Cut Valve By-Pass Valve
The vacuum cut valve and vacuum cut valve bypass valve are installed in parallel on the EVAP purge line between the fuel tank and the EVAP canister. The vacuum cut valve prevents the intake manifold vacuum from being applied to the fuel tank. The vacuum cut valve bypass valve is a solenoid type valve and generally remains closed. It opens only for on board diagnosis. The vacuum cut valve bypass valve responds to signals from the ECM. When the ECM sends an ON (ground) signal, the valve is opened. The vacuum cut valve is then bypassed to apply intake manifold vacuum to the fuel tank.
ON-BOARD REFUELING VAPOR RECOVERY SYSTEM
The ORVR system allows the EVAP canister to store fuel tank vapor created while refueling. During refueling, fuel tank pressure increases, causing the Refueling Control Valve (RCV) to open. With RCV open, fuel tank vapor and air go through the refueling EVAP vapor cut valve, RCV and refueling vapor line to the EVAP canister. The vapor is absorbed by the EVAP canister and the air is vented to the atmosphere. When fuel tank is full, the refueling EVAP vapor cut valve is closed and refueling is stopped. Vapor in the EVAP canister is purged during driving. The RCV is always closed during driving.
MALFUNCTION INDICATOR LIGHT
All vehicles are equipped with a MIL on the instrument panel. Light comes on briefly as a bulb check when the ignition switch is turned to the ON position. Light also comes on when systems related to the emission controls are malfunctioning during normal vehicle operation. For additional information, see appropriate SELF-DIAGNOSTICS article.
INTAKE VALVE TIMING CONTROL SYSTEM
This mechanism hydraulically controls cam phases continuously with the fixed operating angle of the intake valve. The ECM receives signals such as crankshaft position, camshaft position, engine speed and engine coolant temperature. Then, the ECM sends ON/OFF pulse duty signals to the intake valve timing (IVT) control solenoid valve depending on driving status. This makes it possible to control the shut/open timing of the intake valve to increase engine torque in low/mid speed range and output in high-speed range. Intake Valve Timing (IVT) control solenoid valve is activated by ON/OFF pulse duty (ratio) signals from the ECM. The IVT control solenoid valve changes the oil amount and direction of flow through intake valve timing control unit or stops oil flow. The longer pulse width advances valve angle. The shorter pulse width retards valve angle. When ON and OFF pulse widths become equal, the solenoid valve stops oil pressure flow to fix the intake valve angle at the control position.
MISCELLANEOUS CONTROLS
Note. Although not true engine performance-related systems, some controlled devices may affect driveability if they malfunction.
A/C clutch is controlled by ECM through the A/C clutch relay. Under certain conditions, ECM will turn off A/C clutch to improve driveability.
HYDRAULIC COOLING FAN
This system consists of the cooling fan pump, cooling fan drive pump, cooling fan speed control solenoid valve, oil cooler, cooling fan fluid reservoir, etc. The cooling fan pump is operated by engine with the drive belts and provides oil pressure to the cooling fan drive pump which operates the cooling fan. The cooling fan speed control solenoid valve is installed between the cooling fan pump and cooling fan drive pump. The solenoid valve repeats on/off operation according to the signal sent from the ECM. The opening of the solenoid valve varies for optimum engine control. The optimum value stored in the ECM is determined by considering various engine conditions. The ECM controls the cooling fan speed corresponding to the engine speed, the radiator coolant temperature, refrigerant pressure, vehicle speed, air conditioner switch signal, etc. The ECM determines the target fan speed based on the basic fan speed considering the radiator coolant temperature and the engine speed. The ECM controls fan speed between zero and 2550 RPM. When the cooling fan speed control solenoid valve is malfunctioning (does not operate), the cooling fan is operated at the maximum speed by engine through the drive belts.
TRANSMISSION/TRANSAXLE CONTROLS
Automatic Transmission (A/T) models are equipped with an electronic Transmission Control Module (TCM). TCM receives input signals from ECM (RPM signal), idle switch (on-off signal), throttle position sensor (variable signal) and full throttle switch (on-off signal). Based on these values, the TCM calculates optimum timing and duration to energize shift solenoids, overrun clutch solenoid and lock-up solenoid. TCM also indicates when Overdrive (OD) is engaged, by illuminating the OD indicator light.
For more information on TCM, transmission or transaxle controls, refer to appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.