Relays, Sensors, and Control Systems
PGM-FI SystemThe Programmed Fuel Injection (PGM-FI) system is a sequential multiport fuel injection system.
Air conditioning (A/C) Switch
The A/C (air conditioning) switch signals the ECM/PCM whenever there is a demand for cooling.
A/C Compressor Clutch Relay
When the ECM/PCM 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.
Air Fuel Ratio (A/F) Sensor (F23A4 engine)
The A/F Sensor operates over a wide air/fuel range. The A/F Sensor is installed in the exhaust manifold.
Alternator Control
The alternator signals the ECM/PCM during charging. The ECM/PCM 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.
Barometric Pressure (BARO) Sensor
The barometric pressure sensor is inside the ECM/PCM. It converts atmospheric pressure into a voltage signal that modifies the basic duration of the fuel injection discharge.
Crankshaft Position (CKP) and Top Dead Center (TDC) Sensors
The CKP sensor determines fuel injection timing and ignition timing for each cylinder, and also detects engine speed. The TDC sensor determines ignition timing at start-up and when crankshaft position signal is abnormal.
Cylinder Position (CYP) Sensor
The CYP sensor inside the distributor detects the position of the No. 1 cylinder as a reference for sequential fuel injection to each cylinder.
Engine Coolant Temperature (ECT) Sensor
The ECT sensor is a temperature dependent resistor (thermistor). The resistance of the thermistor decreases as the Engine Coolant temperature increases.
Intake Air Temperature (IAT) Sensor
The IAT sensor is a temperature dependent resistor (thermistor). The resistance of the thermistor decreases as the intake air temperature increases.
Ignition Timing Control
The ECM/PCM 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/PCM detects misfiring by using the CKP sensor to monitor fluctuations in crankshaft speed. It will then set DTCs depending on how much misfiring occurs.
Injector Timing and Duration
The ECM/PCM contains the memory for basic discharge duration at various engine speeds and manifold pressures. The basic discharge duration, after being read out 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/PCM detect long term malfunctions in the fuel system and set a Diagnostic Trouble Code (DTC) if the malfunction occurs during two consecutive trips.
Knock Sensor (F23A1, F23A4 engine)
The knock control system adjusts the ignition timing for the octane rating of the gasoline used.
Manifold Absolute Pressure (MAP) Sensor
The MAP sensor converts manifold absolute pressure into electrical signals to the ECM/PCM.
Malfunction Indicator Lamp (MIL) Indication (In relation to Readiness Codes)-F23A4 engine
The vehicle has certain "readiness codes" that are part of the on-board diagnostics for the emissions systems. If the vehicle's battery has been disconnected or gone dead, if the DTCs have been cleared, or if the ECM/PCM has been reset, these codes are reset. In some states, part of the emissions testing is to make sure these codes are set to complete. If all of them are not set to complete, the vehicle may fail the test.
To check if the readiness codes are set, turn the ignition switch ON (II), but do not start the engine. The MIL will come on for 15 - 20 seconds. If it then goes off, the readiness codes are set. If it blinks several times, one or more readiness codes are not set to complete. To set each code, drive the vehicle or run the engine as described in the procedures.
Primary Heated Oxygen sensor (Primary HO(2)S)
The primary HO(2)S detects the oxygen content in the exhaust gas and sends signals to the ECM/PCM which varies the duration of fuel injection accordingly. To stabilize its output, the sensor has an internal heater. The primary HO(2)S is installed in the exhaust manifold. By controlling the air fuel ratio with primary HO(2)S and secondary HO(2)S, the deterioration of the primary HO(2)S 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/PCM sets a DTC.
Secondary Heated Oxygen sensor (Secondary HO(2)S)
The secondary HO(2)S detects the oxygen content in the exhaust gas downstream of the Three Way Catalytic Converter (TWC) and sends signals to the ECM/PCM which varies the duration of fuel injection accordingly. To stabilize its output, the sensor has an internal heater. The secondary HO(2)S is installed in the TWC.
Throttle Position (TP) 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/PCM. The TP sensor is not replaceable apart from the throttle body.
Vehicle Speed Sensor (VSS) (M/T)
The speed sensor is driven by the differential. It generates a pulsed signal from an input of 5 volts. The number of pulses per minute increases/decreases with the speed of the vehicle.