Computers and Control Systems: Description and Operation
PGM-FI SystemThe Programmed Fuel Injection (PGM-FI) system is a sequential multi port fuel injection system.
Alternator Control
The alternator signals the PCM during charging. The PCM then controls the voltage generated at the alternator according to the electrical load determined by the Electrical Load Detector (ELD) and driving mode. This reduces engine load to improve fuel economy
A/C Switch
The A/C (air conditioning) switch signals the PCM whenever there is a demand for cooling.
A/C Compressor Clutch Relay
When the 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.
Barometric Pressure (BARO) Sensor
The Baro sensor is inside the PCM. It converts atmospheric pressure into a voltage signal that modifies the basic duration of the fuel injection discharge.
Camshaft Position (CMP) Sensors (Top Dead Center (TDC) Sensors: '99-01 models)
The CMP (TDC) sensors determine ignition timing at start up (cranking) and when crank angle is abnormal.
Crankshaft Position (CKP) Sensor
The CKP sensor determines timing for injection of each cylinder and also detects engine speed and misfire.
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.
Frame to Powertrain Torque Down Request (FPTDR)
Detects engine retard request signal.
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 PCM contains the memory for basic ignition timing at various engine speeds and manifold absolute pressure. It also adjusts the timing according to engine coolant temperature.
Injector Timing and Duration
The 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 PCM detects long term malfunctions in the fuel system, and will set a Diagnostic Trouble Code (DTC).
Knock Sensor
The knock control system adjusts the ignition timing for the octane rating of the gasoline used.
Malfunction Indicator Lamp (MIL) Indication (In relation to Readiness Codes)
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, these codes are erased. In some states, part of the emissions testing is to make sure these codes are set. If all of them are not set, the test cannot be completed.
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, the readiness codes are not set completely. To reset each code, drive the vehicle or run the engine as described in the procedures to set them in this section.
Manifold Absolute Pressure (MAP) Sensor
The MAP sensor converts manifold absolute pressure into electrical signals to the PCM.
Primary Heated Oxygen Sensors (Primary HO2S)
The primary HO2S detects the oxygen content in the exhaust gas and sends signals to the PCM which varies the duration of injection accordingly. To stabilize its output, the sensor has an internal heater. The Primary HO2S is installed in the exhaust manifold.
By controlling the air fuel ratio with primary HO2S and secondary HO2S, the deterioration of the primary HO2S 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 PCM sets a DTC.
Secondary Heated Oxygen Sensor (Secondary HO2S)
The secondary HO2S detects the oxygen content in the exhaust gas in the downstream of the Three Way Catalytic Converter (TWC) and sends signals to the PCM which varies the duration of injection accordingly. To stabilize its output, the sensor has an internal heater. The secondary HO2S is installed in the TWC.
Starting Control
When the engine is started, the PCM provides a rich mixture by increasing injector duration.
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 PCM. The TP sensor is not replaceable apart from the throttle body.