COMPUTERIZED ENGINE CONTROLS
Computerized engine control system monitors various engine/vehicle functions to control engine operation and lower emissions, while maintaining fuel economy and driveability.
POWERTRAIN CONTROL MODULE (PCM)
Note. Millenia 2.3L, uses an Engine Control Module (ECM). For purpose of this article, all references to PCM include ECM unless otherwise specified.
PCM, through various input sensors, monitors battery voltage, engine RPM, intake air volume, cranking signal, camshaft position, crankshaft position, intake air temperature, radiator and engine coolant temperatures, exhaust oxygen content, throttle position, EGR valve position, atmospheric pressure, gearshift lever position, clutch engagement, braking, power steering operation, and A/C compressor operation.
PCM utilizes this input information to control fuel injection and operation of other output devices. Spark timing is also controlled by PCM.
PCM has a built-in fail-safe mechanism. If a fault occurs while driving, PCM will substitute preprogrammed values. Driving performance will be affected, but vehicle may still be driven.
PCM has a self-diagnostic function, which allows module to store diagnostic trouble codes in its memory. A Malfunction Indicator Light (MIL), located on instrument cluster, informs driver of system problems.
| Application | Location |
|---|---|
| Millenia | Below Center Of Instrument Panel |
ECM/PCM LOCATIONS
Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by PCM. The second category covers OUTPUT SIGNALS, which are components controlled by PCM.
INPUT DEVICES
Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input usage on a specific model, see appropriate wiring diagram in WIRING DIAGRAMS - 2.3L article. The available input signals include the following
A/C Amplifier
A/C amplifier controls A/C operation according to vehicle conditions and sends A/C operation condition signal to PCM.
A/C Pressure Switch
A/C pressure switch detects A/C operation and sends signal to PCM.
Brake Switch
Switch signals PCM of vehicle braking condition.
Closed Throttle Position Switch
Switch detects fully closed throttle plate position and sends signal to PCM. Closed throttle position switch is part of TP sensor, which is adjusted automatically when TP sensor is adjusted.
Coolant Temperature Sensor
See ENGINE COOLANT TEMPERATURE (ECT) SENSOR heading below.
Camshaft Position (CMP) Sensor
CMP sensor detects crankshaft angle at 180-degree intervals (4-cylinder) or 120-degree intervals (V6) and sends signal to PCM. Sensor also detects cylinder No. 1 TDC (4-cylinder) or No. 1 and No. 4 TDC (V6) and sends signal to PCM. For CMP sensor location, see CAMSHAFT POSITION SENSOR LOCATIONS table.
| Application | Location |
|---|---|
| Millenia 2.3L | Right Front Of Engine |
CAMSHAFT POSITION SENSOR LOCATIONS
Clutch Pedal Position Switch (M/T)
Clutch switch signals PCM of clutch operation.
Crankshaft Position (CKP) Sensor
CKP sensor detects crankshaft angle at 60-degree intervals, providing PCM with data to trigger ignition coils, control injection amount and injection timing.
Differential Pressure Feedback EGR (DPFE) Sensor
See EGR SYSTEM under EMISSION SYSTEMS .
EGR Boost Sensor
The EGR boost sensor detects intake manifold pressure and sends a voltage signal to PCM.
EGR Position Sensor
Detects EGR control valve position and sends signal to PCM.
Engine Coolant Temperature (ECT) Sensor
ECT sensor is a thermistor device which changes resistance proportionate to temperature changes. ECT sensor inputs engine coolant temperature to PCM. For ECT sensor location, see IAT SENSOR LOCATIONS table.
| Application | Location |
|---|---|
| Millenia 2.3L | Top Right Side Of Engine |
ECT SENSOR LOCATIONS
Heated Oxygen Sensor (HO2S)
At operating temperature, Heated Oxygen Sensor (HO2S) monitors oxygen content of exhaust gases. A heating circuit is used to warm HO2S to operating temperature, enabling faster conversion of feedback system to closed loop operation.
HO2S produces low voltage (less than .4 volt) to indicate lean mixture (high amount of oxygen) and a high voltage (more than .6 volt) to indicate rich mixture (low amount of oxygen). This voltage signal is transmitted to PCM. All models use more than one sensor.
Intake Air Temperature (IAT) Sensor
IAT sensor inputs air temperature to the PCM. The IAT sensor changes resistance in response to air temperature. The IAT sensor resistance decreases as air temperature increases. For IAT sensor location, see IAT SENSOR LOCATIONS table.
| Application | Location |
|---|---|
| Millenia 2.3L | (1) |
| (1) Millenia 2.3L is equipped with 3 IAT sensors. One IAT sensor is located in air filter housing, another sensor is located in dynamic chamber at right rear or engine and remaining IAT sensor is located in Lysholm compressor on top right of engine. | |
| (1) | Millenia 2.3L is equipped with 3 IAT sensors. One IAT sensor is located in air filter housing, another sensor is located in dynamic chamber at right rear or engine and remaining IAT sensor is located in Lysholm compressor on top right of engine. |
IAT SENSOR LOCATIONS
Knock Sensor
Knock sensor transmits signal to PCM which retards ignition timing when knocking occurs.
Main Relay
Main relay provides battery voltage to PCM and injectors.
Mass Airflow (MAF) Sensor
MAF sensor measures flow of air entering engine. This measurement of airflow is a reflection of engine load (throttle opening). Sensing element (hot wire) is a thin platinum wire wound on a ceramic bobbin and coated with glass.
Hot wire is maintained at 392°F (200°C) above cold wire (ambient) temperature. Cold wire is located downstream of hot wire. As air passes through airflow sensor, air temperature is measured as air passes over cold wire sensor. PCM uses this information to control fuel delivery.
Manifold Absolute Pressure (MAP) Sensor (Millenia 2.3L)
MAP sensor varies voltage signal to PCM in relation to intake manifold pressure.
Neutral Switch (M/T)
Neutral switch signals PCM of transaxle gear selection.
Power Steering Pressure Switch
Detects power steering operation and sends signal to PCM.
Speedometer Sensor
Speedometer sensor is located in the instrument cluster. Speedometer sensor detects the pulse signal (sine wave) from the Vehicle Speed Sensor (VSS) and sends a vehicle speed signal (square wave) to PCM.
Throttle Position (TP) Sensor
TP sensor provides signal in response to throttle plate position.
Vehicle Speed Sensor (VSS)
VSS located on transmission, is a magnetic pickup type sensor that detects vehicle speed.
OUTPUT SIGNALS
Note. Vehicles are equipped with various combinations of computer-controlled components. Not all components listed are used on every vehicle. For theory and operation of each output component, refer to system indicated after component.
The PCM processes information from input sensors and sends appropriate voltage control signals to the following engine controls
A/C Cut-Out System
See IDLE SPEED under FUEL SYSTEM.
By-Pass Air Control (BAC) Valve
See IDLE SPEED under FUEL SYSTEM.
Canister Purge Solenoid
See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS.
Malfunction Indicator Light (MIL)
See SELF-DIAGNOSTIC SYSTEM .
Fuel Injectors
See FUEL CONTROL .
Fuel Pump
See FUEL DELIVERY under FUEL SYSTEM.
Fuel Pump Relay
See FUEL DELIVERY under FUEL SYSTEM.
Idle Air Control (IAC) Valve
See IDLE SPEED under FUEL SYSTEM.
Ignition Timing Advance Control
See IGNITION TIMING CONTROL SYSTEMS under IGNITION SYSTEMS.
Pressure Regulator Control (PRC) Solenoid
See FUEL DELIVERY under FUEL SYSTEM.
Fuel, pressurized by electric fuel pump, flows through fuel filter, injector fuel rail and fuel pressure regulator. Pump is located in fuel tank. PCM controls fuel pump relay ground circuit during run and start modes.
The PCM activates fuel pump relay based on inputs from the ignition switch and the camshaft position sensor signal. During cranking, ignition switch cranking circuit energizes fuel pump relay. After engine starts and key is released to RUN position (engine speed more than 50 RPM), PCM provides fuel pump relay ground.
Fuel Pressure Regulator
Pressure regulator is a sealed unit, divided into 2 chambers (fuel and spring chambers) by a diaphragm. The fuel chamber receives fuel through the inlet side of injector fuel rail. The spring chamber is connected to intake manifold vacuum.
At idle, intake manifold vacuum is high. The diaphragm is pulled back by intake manifold vacuum, and excess fuel is returned to fuel tank. As throttle opens, intake manifold vacuum decreases. The regulator spring overcomes manifold vacuum, increasing fuel pressure.
PRC system includes a solenoid connected to vacuum line of fuel pressure regulator. During hot engine restarts, PCM energizes PRC solenoid. This prevents intake manifold vacuum from going to fuel pressure regulator and increases fuel pressure about 8 psi (.6 kg/cm 2 ).
The PCM controls fuel injector ON time (pulse width) to meter fuel quantity into intake ports. The PCM receives inputs from engine sensors to compute fuel flow necessary to maintain correct air/fuel operation throughout engine operating range.
Each cylinder has a solenoid-operated injector that sprays fuel toward each intake valve. Each injector receives battery voltage from main relay. The PCM-controlled ground circuit is used to complete the circuit and energize the injector. Fuel injectors "fire" sequentially (in engine firing order) once per complete cycle.
Injectors consist of solenoid-actuated pintle and needle valve assembly. Amount of fuel delivered to engine is regulated by length of time solenoid is energized (pulse width). Atomized spray pattern is obtained by shape of injector pintle.
During acceleration (60 percent throttle or more with transmission in gear and clutch pedal released) and about 5 seconds after starting the engine, the PCM opens A/C relay, cutting off power to A/C compressor clutch. This improves idle after start-up and during heavy acceleration. A/C is cut off for about 10 seconds.
The BAC valve contains an air valve and Idle Air Control (IAC) valve. Engine coolant is directed around the air valve, warming the thermowax element. When engine coolant temperature is less than 122°F (50°C), the wax is contracted and the engine idles fast. When coolant temperature is more than 122°F (50°C), the wax is fully expanded, closing valve.
The IAC valve, controlled by PCM, regulates air by-pass during cold and warm engine operation. During cold engine operation, the IAC valve opens, raising fast idle speed to a predetermined RPM. The IAC valve also compensates for all engine loads during warm engine operation to maintain a preset idle RPM.
IAC valve is an electromechanical device control by PCM. The IAC valve is mounted on throttle body and allows air to by-pass the throttle plate. The amount of air allowed to by-pass the throttle plate is determined by PCM and is controlled by a duty signal.
Millenia 2.3L
The distributorless ignition system uses a camshaft position sensor to control ignition timing. On Millenia 2.3L, 6 individual ignition coils are used, one located on each spark plug.
The camshaft position sensor, located at right front of engine, monitors TDC of cylinder No. 1 and crankshaft angle at 180-degree intervals. Signals created by camshaft position sensor are sent to PCM.
PCM delivers ignition signals to the ignitor to control ignition. Ignitor triggers appropriate ignition coil. Power for ignition coils is supplied from ignition switch.
All models use a PCM-controlled Electronic Spark Advance (ESA) system. The PCM determines ignition timing based on signals from input devices.
EMISSION SYSTEMS
Note. Not all listed components are used on every vehicle system. Component usage depends on calibration of vehicle. See the VACUUM DIAGRAMS - 2.3L article.
DECELERATION CONTROL SYSTEM
Fuel injected engines include a system to reduce emission during deceleration during closed throttle and high RPM conditions. At speeds greater than 2000 RPM, PCM shuts off fuel injection whenever TP sensor detects closed throttle position.
EXHAUST GAS RECIRCULATION (EGR)
EGR system allows measured amounts of exhaust gas into intake manifold to reduce oxides of nitrogen (NOx).
EGR system on Millenia consists of EGR control valve, EGR solenoid valves (vacuum side and vent side), EGR position sensor, connecting hoses and pipes.
FUEL EVAPORATION SYSTEM
Fuel evaporation system prevents escape of raw fuel vapor to atmosphere. System components include fuel tank with integral vapor separator, check-and-cut valve, purge control solenoid valve, charcoal canister, fuel filler cap and connecting lines. Additional components include a 2-way check valve and PCM.
Canister Purge Solenoid Valve
This normally-closed solenoid valve controls fuel vapor flow from canister to intake manifold. Solenoid is opened or closed by a signal from PCM during various engine operating modes.
Vapor Vent System
All vapor valves are mounted on fuel tank and use a small orifice which allows vapor (but not liquid) fuel to pass into line running to canister. Fuel vapors in fuel tank are vented though vapor valve assembly on top of fuel tank. Vapors are routed through a vapor line to carbon canister in engine compartment.
POSITIVE CRANKCASE VENTILATION (PCV)
The PCV system uses intake manifold vacuum to eliminate crankcase pressure. Manifold vacuum draws gases from crankcase, through PCV hose, into combustion chamber. The PCV valve is positioned in hose through which crankcase gases flow on their way to combustion chamber.
By opening and closing in direct relation to engine vacuum, the PCV valve meters crankcase gas flow to combustion chamber. During periods of high manifold vacuum, such as at idle and deceleration, valve is almost completely closed, limiting flow of gases. During cruise speeds, valve permits greatest flow of gases.
Under conditions in which excessively high amounts of crankcase pressure are produced (such as heavy load), system allows excess gases to flow back through crankcase vent hose and into intake manifold.
Also called CHECK ENGINE light, MIL comes on when ignition is turned on. Light remains on for several seconds after engine has started. If an abnormal input signal occurs, light comes on and Diagnostic Trouble Code (DTC) is stored in memory. If the abnormal input signal returns to normal, PCM turns light off but DTC remains stored in memory until cleared. If ignition is turned on again, light will not come on until PCM detects another malfunction during system operation.
Note. PCM diagnostic memory is retained by direct power supply from battery. Memory is not erased by turning off ignition but, is erased if battery or PCM is disconnected.
MISCELLANEOUS CONTROLS
Note. Although not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.
A/C CLUTCH CYCLING PRESSURE SWITCH (CCPS)
On models with manual A/C system, the CCPS is mounted on top of the receiver-drier. Based on refrigerant system pressure, a signal is sent to the PCM. The PCM uses this signal to maintain system pressure within the programmed range.
WIDE OPEN THROTTLE A/C (WAC) CUTOFF
During wide open throttle, WAC circuit interrupts power to A/C compressor clutch. The A/C remains off for about 3 seconds after returning from WOT.