Relays, Sensors, and Control Systems
SYSTEM DESCRIPTIONPGM-FI System
The Programmed Fuel Injection (PGM-FI) system is a sequential multi port fuel injection system.
Fuel Injector Timing and Duration
The ECM contains the memory for basic discharge duration at various engine speeds and manifold pressures. The basic discharge duration, after being readout from the memory, is further modified by signals sent from various sensors to obtain the final discharge duration.
By monitoring Long Term Fuel Trim, the ECM detects long term malfunctions in the fuel system, and will set a Diagnostic Trouble Code (DTC) if the malfunction occurs during two consecutive trips.
Ignition Timing Control
The ECM contains the memory for basic ignition timing at various engine speeds and manifold air flow rates. It also adjusts the timing according to engine coolant temperature. The ECM detects misfiring by using the CKP sensor to monitor fluctuations in crankshaft speed. It will then set DTCs depending on how much misfiring occurs.
Starting Control
When the engine is started, the ECM provides a rich mixture by increasing fuel injector duration.
Alternator Control
The alternator signals the ECM during charging. The ECM then controls the voltage generated at the alternator according to the electrical load determined by the ELD (Electrical Load Detector) and driving mode. This reduces engine load to improve fuel economy.
A/C Switch
The A/C (air conditioning) switch signals the ECM whenever there is a demand for cooling.
A/C Compressor Clutch Relay
When the ECM receives a demand for cooling from the A/C system, it delays the compressor from being energized, and enriches the mixture to assure smooth transition to the A/C mode.
TDC (Top Dead Center) 1 and 2 / CKP ( Crankshaft Position) Sensors
The TDC 1 and TDC 2 sensors detect the position of the No.1 cylinder as a reference for sequential fuel injection to each cylinder. The CKP sensor detects engine speed and determines ignition timing and timing for fuel injection of each cylinder.
MAP (Manifold Absolute Pressure) Sensor
The MAP sensor convents manifold absolute pressure into electrical signals to the ECM.
IAT (Intake Air Temperature) Sensor
The IAT sensor is a temperature dependent resistor (thermistor). The resistance of the thermistor decreases as the intake air temperature increases.
ECT (Engine Coolant Temperature) Sensor
The ECT sensor is a temperature dependent resistor (thermistor). The resistance of the thermistor decreases as the engine coolant temperature increases.
TP (Throttle Position) Sensor
The TP sensor is a potentiometer connected to the throttle valve shaft. As the throttle position changes, the sensor varies the signal voltage to the ECM. The TP sensor is not replaceable apart from the throttle body.
BARO (Barometric Pressure) Sensor
The barometric pressure sensor is inside the ECM. It converts atmospheric pressure into a voltage signal that modifies the basic duration of the fuel injection discharge.
Primary and Secondary HO2S (Heated Oxygen sensors)
The heated oxygen sensors detect the oxygen content in the exhaust gas and send signals to the ECM which varies the duration of fuel injection accordingly. To stabilize its output, the sensors have an internal heater. The primary sensor is installed in the exhaust pipe. The secondary sensor is installed in the TWC.
By controlling the air/fuel ratio with sensors, the deterioration of the primary sensor can be evaluated by its feedback period. When the feedback period exceeds a certain value during stable driving conditions, the sensor is considered deteriorated and the ECM sets a DTC.
Knock Sensor
The knock control system adjusts the ignition timing for the octane rating of the gasoline used.
Electronic Control System
The functions of the fuel and emission control systems are managed by the engine control module (ECM).
Fail-safe Function
When an abnormality occurs in a signal from a sensor, the ECM ignores that signal and assumes a pre-programmed value for that sensor that allows the engine to continue to run.
Back-up Function
When an abnormality occurs in the ECM itself the fuel injectors are controlled by a back-up circuit independent of the system in order to permit minimal driving.
Self-diagnosis [Malfunction Indicator Lamp (MIL)]
When an abnormality occurs in the signal from a sensor, the ECM supplies ground for the MIL and stores the DTC in erasable memory. When the ignition is first turned on, the ECM supplies ground for the MIL for two seconds to check the MIL bulb condition.
Two Driving Cycle Detection Method
To prevent false indications, the "two driving cycle detection method" is used for the fuel metering-related, idle control system, ECT sensor, TWC, EVAP control system and other self-diagnostic functions. When an abnormality occurs, the ECM stores it in its memory. When the same abnormality recurs after the ignition switch is turned OFF and ON (II) again, the ECM informs the driver by turning on the MIL.