Prizm L4-1600cc 1.6L DOHC VIN 5 (1989)
Engine Control Module: Description and Operation
The Computer Command Control (CCC) system, which is controlled by the Electronic Control Module (ECM), is designed to maintain exhaust emission
levels at federal standards while providing good driveability and fuel efficiency. The functions of the system are based on data gathered by sensors and
switches located throughout the vehicle. The ECM maintains control over fuel delivery, ignition, idle air flow, the fuel pump and other system
components, while monitoring the system for faulty operation with its diagnostic capabilities. It is important to review the component sections and wiring
diagrams to determine which systems are controlled by the ECM.
The ECM is a solid state integrated component that is an essential part of the electronic control system, its functions include not only control of, fuel
injectors, ISC solenoid valve, circuit opening relay, etc. but also a self-diagnosis function and a fail-safe function.
The ECM diagnoses troubles which may occur in any of its systems by monitoring the input signals it receives and comparing them to the values it has
stored in its memory. If the signals are not within the preset values, it indicates that a fault has occurred. It indicates this by turning on, or flashing the
"CHECK ENGINE" light when a fault occurs in any of the following systems:
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Oxygen (02) Sensor.
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Coolant Temperature Sensor (CTS).
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Throttle Switch (TS).
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Manifold Air Temperature (MAT) Sensor.
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Manifold Absolute Pressure (MAP) Sensor.
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Ignition Signal.
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Crank Angle Sensor.
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Vehicle Speed Sensor (VSS).
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Exhaust Gas Recirculation (EGR) system.
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Central Processing Unit (CPU) of ECM.
The ECM also indicates trouble codes in its memory by means of flashing the "CHECK ENGINE" light at the time of inspection. Even when a trouble
has occurred in the EFI system and a fault is detected by the ECM, control over the operating systems is maintained on the basis of the standard signals
and/or back-up program prestored in the ECM. This function is called "FAIL-SAFE" function. Thus, with this function, a certain level of engine
performance is available even when some failures occur.
