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. Input devices supply the computer with signals which indicate operating conditions of the vehicle. Output signals control systems which control vehicle operation. Operational parameters are programmed into computer memory.
POWERTRAIN CONTROL MODULE
The Powertrain Control Module (PCM), through various input sensors, monitors air intake air temperature, atmospheric pressure, coolant temperature, engine RPM and exhaust oxygen content. PCM uses this input information to control fuel injection and operation of other output devices.
PCM has a self-diagnostic function, which allows unit to store a number of trouble codes in its memory. If a failure exists, PCM will inform the driver by turning on Malfunction Indicator Light (MIL) on instrument cluster.
| Application | Location |
|---|---|
| Sephia | Below Center Of Instrument Panel, Mounted On Floorboard, Under Carpet |
PCM LOCATION
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 input device usage on a specific model, see appropriate wiring diagram in appropriate WIRING DIAGRAMS article. Available input signals include the following
A/C Relay
Sends signal to PCM when energized.
A/C Switch
Switch closes when A/C or blower is on.
Atmospheric Pressure Sensor
Sensor varies voltage signal according to altitude. Sensor is located inside of PCM.
Brake Pedal Switch
Switch signals PCM of vehicle braking condition.
Camshaft Position (CMP) Sensor
CMP sensor is located in distributor and detects SGC (piston No. 1 signal) and SGT (180-degree signal) to be sent to PCM.
Closed Throttle Position Switch
Signals PCM when throttle is closed.
Clutch Pedal Position Switch (M/T)
Signals PCM of clutch operation. Switch is off with clutch depressed.
Crankshaft Position (CKP) Sensor
CKP sensor provides signals for fuel injection and ignition timing.
EGR Differential Pressure Sensor
Sends EGR pressure or barometric pressure signal to PCM.
EGR Valve Position Sensor
Sensor sends EGR position signal to PCM.
Engine Coolant Temperature (ECT) Sensor
ECT sensor inputs coolant temperature to PCM.
Heated Oxygen Sensors (HO2S)
Generates voltage signal depending on oxygen content of exhaust. Located in front and behind converter to monitor converter efficiency.
Ignitor
Triggers coil and signals engine speed to tachometer.
Intake Air Temperature (IAT) Sensor
IAT sensor provides electronic fuel injection system with mixture temperature information. The IAT sensor is used both as a density corrector for airflow calculation and to proportion cold enrichment fuel flow. Sensor is located inside MAF sensor.
Knock Sensor
Generates voltage signal when knock is detected. Knock sensor is located on side of engine, below intake manifold.
Mass Airflow (MAF) Sensor
MAF sensor measures flow of air entering the engine. This measurement of airflow is a reflection of engine load (throttle opening). The sensing element (hot wire) is a thin platinum wire wound on a ceramic bobbin and coated with glass.
The hot wire is maintained at 392°F (200°C) greater than a downstream cold (ambient) temperature wire. As airflow through the airflow sensor increases, the temperature of the hot wire drops. The PCM must then increase current flow through the hot wire to maintain the desired temperature. This increased current requirement is a direct reflection of airflow volume. The PCM uses this information to control fuel delivery.
Main Relay
Provides battery voltage to PCM and injectors.
Neutral Position Switch (M/T)
Signals PCM of transaxle gear selection.
Power Steering Pressure Switch
Signals PCM of power steering load on engine.
Throttle Position (TP) Sensor
Provides signal in response to throttle position.
Tank Pressure Sensor
Monitors EVAP system pressure to check for leaks.
Transmission Range Switch (A/T)
Signals in-gear position to PCM. On when in Park or Neutral.
Vehicle Speed Sensor
Sends a pulsing signal to PCM when vehicle is moving.
OUTPUT SIGNALS
Note. For theory and operation on each output component, refer to the 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.
EGR System
See EGR SYSTEM under EMISSION SYSTEMS.
Malfunction Indicator Light (MIL)
See SELF-DIAGNOSTIC SYSTEM .
Fuel Pressure Regulator Control (FPRC) Solenoid
See FUEL DELIVERY under FUEL SYSTEM.
Ignition Timing Advance Control
See IGNITION TIMING CONTROL SYSTEMS under IGNITION SYSTEMS.
Purge Control Solenoid Valve
See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS.
Tank Pressure Control Valve
See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS.
VICS System (1.6L)
See VICS SYSTEM under EMISSION SYSTEMS.
Fuel Pump
Fuel, pressurized by electric fuel pump, flows through fuel filter, injector fuel rail and fuel pressure regulator. Pump is located in fuel tank.
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, gradually blocking off fuel return passage and increasing fuel pressure.
FPRC system includes a solenoid connected to vacuum line of fuel pressure regulator. During hot engine restarts, PCM energizes FPRC solenoid. This prevents intake manifold vacuum from going to fuel pressure regulator and increases fuel pressure about 8 psi (.6 kg/cm 2 ).
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. When engine temperature is 230°F (110°C) or more, PCM cycles A/C relay 10 seconds on and 10 seconds off until engine temperature is 225°F (107°C) or less.
Idle Air Control (IAC) Solenoid
IAC solenoid is an electromechanical device controlled by PCM. The IAC solenoid is mounted on the 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 controlled by a duty signal.
DISTRIBUTOR IGNITION SYSTEM
Light Emitting Diode (LED) sensors are used to detect position of a rotating shutter wheel located inside of distributor. As each segment of the shutter wheel passes between the LED and light source, a change in current occurs. The LED responds to the change in light by switching a transistor on or off.
This signal is used by PCM to detect the position of each cylinder or TDC of cylinder No. 1. The PCM delivers ignition signals to the ignitor to control ignition. Ignitor triggers ignition coil.
A PCM-controlled Electronic Spark Advance (ESA) system is used. The PCM determines ignition timing based on signals from input devices.
DECHOKE CONTROL SYSTEM
To aid engine start-up when spark plugs become fouled, fuel injection is shut off when throttle is held wide open while cranking. Engine coolant temperature must be 32°F (0°C) or less (except 1.6L). This allows spark plugs to dry and purges excess fuel from cylinders.
The EGR system recirculates a small amount of exhaust gas into intake manifold to reduce combustion temperature, and reduce NOx emissions. EGR system consists of EGR valve, EGR position sensor, EGR vacuum control solenoid, EGR vent control solenoid, EGR pressure sensor (1.6L), EGR boost sensor and solenoid (1.8L), PCM and input devices.
EGR Valve
EGR valve is vacuum operated. The EGR valve is operated by a vacuum signal controlled by PCM through various solenoids.
EGR Control Solenoids
EGR control solenoids (vent and vacuum) control vacuum output to EGR valve. When EGR control solenoids are de-energized, solenoid valves are closed. When solenoid valves are energized, solenoid valves open, allowing manifold vacuum to be applied to EGR valve, or vented.
EGR Boost Sensor/EGR Pressure Sensor
PCM monitors EGR boost sensor (1.8L) or EGR pressure sensor (1.6L) to check EGR operation and measure barometric pressure.
EGR Boost Sensor Solenoid
EGR boost sensor solenoid switches between EGR and vent to allow monitoring of EGR operation and measure barometric pressure.
Sensor varies voltage according to valve position.
FUEL EVAPORATION SYSTEM
Fuel evaporation system prevents escape of raw fuel vapor to atmosphere. System components include fuel tank, vapor separator, 2-way check valve, purge control solenoid valve, charcoal canister, fuel filler cap, connecting lines and PCM.
This normally-closed solenoid valve controls fuel vapor flow from canister to intake manifold. It is opened or closed by a signal from PCM during various engine operating systemmodes.
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 is produced (such as heavy load), system allows excess gases to flow back through crankcase vent hose and into intake tract.
VICS SYSTEM
Variable Inertia Charging System (VICS) is used on 1.6L engine to broaden torque band. As engine reaches 4750 RPM, a shutter valve controlled by the PCM opens, changing resonance path in intake manifold.
Also called CHECK ENGINE light, MIL comes on when ignition is turned on. MIL remains on for several seconds after engine has started. If an abnormal input signal occurs, light stays on and code is stored in memory. If the abnormal input signal returns to normal, PCM turns light off but code remains stored in memory until cleared. If ignition is turned on again, light will remain off 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.