California

OPERATION
The Electronic Engine Control System (EEC IV) includes Powertrain Control Module (PCM) and Ignition Control Module (ICM), which receive inputs from various sensors. The PCM and ICM use this information to control Fuel Flow, Evaporative Emissions and Ignition. These three systems and the PCM and ICM work together to provide improved fuel economy and performance, and lower exhaust emissions.

SUBSYSTEMS AND COMPONENTS

PCM Power Relay
The PCM Power relay supplies power to the PCM, ICM module and EEC system-related components. When the ignition switch is turned to "START" or "RUN", voltage is applied to the PCM power relay coil, and the relay's contacts close. This allows voltage to be applied from EEC power fuse in the engine compartment fuse/relay box, through the relay's contacts to the PCM, ICM, fuel pump relay, WOT cutout relay, fuel injectors, idle air control (IAC) Valve, canister purge Solenoid, A4LD transmission (if equipped), and Mass Air Flow (MAF) Sensor.

Fuel Flow
The engine uses an Electronic Fuel Injection (EFI) System. Fuel is injected into the engine by the fuel injectors located above each intake valve. The duration and timing of the six fuel injectors are controlled by the PCM according to the inputs it receives from various engine sensors.

The electric fuel pump supplies fuel under pressure to the fuel injectors. When the ignition switch is turned to "RUN" or "START", voltage is applied from the PCM relay to the fuel pump relay coil. The coil is grounded by the PCM, and the relay's contacts close. Voltage is now applied from the fuel pump fuse in the engine compartment fuse/relay box, through the relay's contacts and the inertia fuel shut-off switch to the fuel pump. The inertia fuel shutoff switch is a safety device that cuts off voltage to the fuel pump in the event of a collision. Once the inertia fuel shut-off switch opens, it must be reset manually.

Canister Purge
The carbon canister collects fuel vapors from the fuel tank and other components to be burned later in the engine. The canister purge solenoid is controlled by the PCM. When the PCM grounds the canister purge solenoid, the vapors are released to the engine for burning.

Ignition
The EEC System has a special Ignition Control Module (ICM) that has no magnetic pickup or vacuum advance mechanisms. Instead, all ignition timing is controlled by the PCM and ICM.

Mass Air Flow (MAF) Sensor
The Mass Air Flow (MAF) Sensor directly measures the mass of the air flowing into the engine. The sensor output is used by the PCM to calculate the injector pulse width for proper air/fuel ratio.

A4LD Transmission (IF EQUIPPED)
The A4LD transmission is an electronically controlled four speed automatic transmission. The Powertrain Control Module (PCM) uses inputs from various sensors to control the operation of the A4LD transmission.

The A4LD transmission has self-test capabilities much like those in other electronic control systems.

The PCM power relay supplies power to the PCM and PCM system-related components. When the ignition switch is turned to "RUN" or "START", voltage is applied to the PCM power relay coil, closing the relay's contacts. Voltage is supplied to the shift solenoid and the Torque Converter Clutch (TCC) Solenoid, through the PCM power relay.

The Throttle Position (TP) Sensor is a potentiometer. The sensor output is a DC voltage that varies with throttle angle. By monitoring the TP Sensor output and other sensors, the PCM calculates the proper transmission line pressure, shift scheduling, and torque converter clutch.

The Profile Ignition Pickup (PIP) signal is produced by Electronic Ignition (EI). It sends RPM and crankshaft position information to the PCM to determine shift scheduling and torque converter operation.

The shift solenoid provides gear selection of third and fourth gears by controlling the pressure to the shift valves.

The Torque Converter Clutch (TCC) Solenoid provides the torque converter clutch control by shifting the converter clutch control valve to apply or release the torque converter clutch.

The Vehicle Speed Sensor (VSS) generates an AC signal that is proportional to vehicle speed.

The PCM uses this speed signal and other inputs to determine the shift scheduling and converter clutch control.

The Brake On/Off (BOO) Switch is used to prevent converter clutch operation when the brake has been depressed.

This input is ignored if the Throttle Position (TP) Sensor indicates more than one third throttle position.

The Engine Coolant Temperature Sensor (ECT) is a thermistor in which resistance decreases as engine coolant temperature increases. The PCM measures the voltage drop across the engine coolant temperature sensor and uses this information to help calculate fuel delivery, spark timing and EGR control and clutch converter operation.

Idle Air Control (IAC) Valve
The Idle Air Control (IAC) Valve controls engine idle speed by regulating the amount of air allowed to pass around the throttle plates. This permits the PCM to make idle speed corrections to prevent engine stall during cold engine warm-ups as engine load changes.

Throttle Position (TP) Sensor
The Throttle Position (TP) Sensor is a potentiometer. The sensor output is a DC voltage that varies with throttle plate angle. By monitoring the throttle position (TP) sensor output, the PCM calculates fuel delivery requirements based on driver demand.

Heated Oxygen Sensor (HO2S)
The Heated Oxygen Sensor (HO2S) provides a voltage signal to the PCM for regulating the air/fuel ratio by sensing the oxygen content of the exhaust gases. Too much oxygen indicates a lean mixture, while too little oxygen indicates a rich mixture.

Engine Coolant Temperature (ECT) Sensor
The Engine Coolant Temperature (ECT) Sensor is a thermistor whose resistance decreases as engine coolant temperature increases, and increases as engine coolant temperature decreases. The PCM measures the voltage drop across the engine coolant temperature (ECT) sensor and uses this information to calculate fuel delivery, spark timing and EGR control.

Intake Air Temperature (IAT) Sensor
The Intake Air Temperature (IAT) Sensor is a thermistor whose resistance decreases as manifold air temperature increases, and increases as manifold air temperature decreases (negative temperature coefficient). The PCM measures the voltage drop across the Intake air temperature (IAT) sensor and uses this information to calculate fuel delivery, spark timing and EGR control.

Vehicle Speed Sensor (VSS)
The Vehicle Speed Sensor (VSS) generates an AC signal that is proportional to vehicle speed. The AC signal is sent to the PCM and is used for engine management and speed control (if equipped).

Data Link Connector (DLC) And Self-test Input (STI) Connector
These two connectors are used for diagnostic procedures pertaining to the PCM. The PCM stores a self-test program in its permanent memory. When activated, it checks the EEC system by testing the PCM and verifies that various sensors and actuators are connected and operating properly.

Pressure Feedback EGR (PFE) Sensor
he Pressure Feedback EGR Sensor (PFE) is a transducer that monitors the pressure drop across an orifice that EGR flows through. The PCM uses this feedback signal from the transducer to control EGR flow.

EGR Vacuum Regulator (EVR) Solenoid
The PCM controls exhaust gas recirculation by varying the voltage applied to the EGR Vacuum Regulator (EVR) Solenoid. The EVR then regulates the vacuum level present at the EGR valve to control exhaust gas flow into the intake manifold.