Tracker 2WD L4-2.0L VIN C (1999)
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Central Processing Unit (CPU) of the PCM
When the PCM detects a malfunction in one of the above areas, the PCM will illuminate or flash the MIL in order to notify the driver of the occurrence
of a fault. The PCM will store a Diagnostic Trouble Code (DTC) when the PCM illuminates the MIL.
The PCM will turn off the MIL after 3 consecutive ignition cycles, in which the diagnostic runs, without the malfunction occurring. The DTC will remain
stored in the PCM memory after the MIL is OFF.
Fail-Safe Function
When a malfunction occurs within the engine control system, the PCM maintains control over the fuel injection system, the idle speed control system,
etc. The PCM controls these systems by using calculated values and backup programs stored within the PCM.
This function is called the fail-safe function. With the fail-safe function, a certain level of engine performance is available even when a malfunction
occurs. The fail-safe function prevents a complete loss of engine performance.
The systems covered by the fail-safe function are as follows:
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The Engine Coolant Temperature (ECT) Sensor
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The Throttle Position (TP) Sensor
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Mass Air Flow (MAF) Sensor
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The Intake Air Temperature (IAT) Sensor
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The Vehicle Speed Sensor (VSS)
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The Barometric (BARO) Pressure Sensor
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Fuel level sensor
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The Central Processing Unit (CPU) in the PCM
Control Module Learning Ability
The control module has a learning ability which enables the control module to make corrections for minor variations in the fuel system. This learning
ability can improve driveability. Disconnecting the battery resets the learning process. A change in the vehicles performance may be noticed when a reset
occurs. The vehicle operator can teach the control module in order to regain some of the lost vehicle performance.
In order to teach the control module, ensure that the engine is at operating temperature and drive the vehicle at part throttle with moderate acceleration.
The vehicle may also be operated at idle conditions until normal performance returns.
Input Components
The PCM supplies a buffered voltage to the various information sensors and switches. The PCM monitors the input components for circuit continuity
and out-of-range values. The PCM also provides performance checking. Performance checking refers to the PCM indicating a fault when the signal from
an input does not seem reasonable (i.e. a Throttle Position (TP) sensor that indicates high throttle position at low engine loads or low manifold absolute
pressure sensor voltage). The input components may include, but are not limited to the following sensors and switches:
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Vehicle Speed Sensor (VSS)
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Crankshaft Position (CKP) Sensor
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Throttle position (TP) sensor
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Engine Coolant Temperature (ECT) Sensor
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Camshaft Position (CMP) Sensor
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Mass Air Flow (MAF) Sensor
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Manifold Absolute Pressure (MAP) Sensor
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Heated Oxygen Sensors (HO2S)
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Fuel tank pressure sensor
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Fuel level sensor
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Diode module
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Power Steering Pressure (PSP) switch, if equipped
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Transmission range switch, automatic transmission only
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Clutch Pedal Position (CPP) switch, manual transmission only
For more information on some of the PCM input components, refer to Information Sensors/Switches Description.
Output Components
The PCM is responsible for the control and operation of many output components. The PCM controls many components with an electronic switch that
completes a ground circuit when turned on. The PCM monitors the output components for the proper response to the PCM commands. Components
where functional monitoring is not feasible will be monitored for circuit continuity and out-of-range values if applicable.
Output components to be monitored include, but are not limited to the following circuits:
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The Idle Air Control (IAC) valve
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The main relay
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The Malfunction Indicator Lamp (MIL) control
