Vibe L4-1.8L VIN L (2003)
Engine Control Module: Description and Operation
The powertrain control module (PCM) is a precision 32-bit microprocessor and is an essential part of the electronic control system. The PCM is
responsible for such major functions as control of the fuel injectors, the idle air control (IAC) valve, the fuel pump relay, etc. The PCM (1) is located
below the instrument panel (IP) storage compartment. Communication with the PCM is through the data link connector (2) located on the left side below
the IP.
The PCM performs the OBD II diagnostic tests of the emission related systems. The PCM supplies a buffered voltage, called reference voltage, to the
various information sensors and switches. The PCM controls most components with an electronic switch that completes a ground circuit when turned
ON. The electronic switch is commonly referred to as an output driver. The PCM is also responsible for a self-diagnosis function and a fail-safe function.
Self-Diagnosis Function
The powertrain control module (PCM) diagnoses any troubles which may occur in the engine control system when the ignition switch is in the ON
position with the engine running. The PCM indicates a malfunction by illuminating the malfunction indicator lamp (MIL) when a fault occurs in any of
the following systems:
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The heated oxygen sensor 1 (HO2S 1)
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The heated oxygen sensor 2 (HO2S 2)
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The engine coolant temperature (ECT) sensor
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The throttle position (TP) sensor (including the CTP switch)
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The vehicle speed sensor (VSS)
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The intake air temperature (IAT) sensor
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The mass air flow (MAF) sensor
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The camshaft position (CMP) sensor
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The crankshaft position (CKP) sensor
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The knock sensor (KS) system
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The evaporative emission (EVAP) control system
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The idle air control (IAC) system
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The CMP actuator solenoid system
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The misfire detection
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The fuel-trim
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The catalyst monitor
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The 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.
Malfunction Indicator Lamp (MIL) Operation
The malfunction indicator lamp (MIL) is located in the instrument panel cluster. The MIL will display as either SERVICE ENGINE SOON or one of
the following symbols when commanded ON:
The MIL indicates that an emissions related fault has occurred and vehicle service is required.
The following is a list of the modes of operation for the MIL:
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The MIL illuminates when the ignition is turned ON, with the engine OFF. This is a bulb test to ensure the MIL is able to illuminate.
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The MIL turns OFF after the engine is started if a diagnostic fault is not present.
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The MIL remains illuminated after the engine is started if the control module detects a fault. A diagnostic trouble code (DTC) is stored any time
the control module illuminates the MIL due to an emissions related fault. The MIL turns OFF after three consecutive ignition cycles in which a
Test Passed has been reported for the diagnostic test that originally caused the MIL to illuminate.
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The MIL flashes if the control module detects a misfire condition which could damage the catalytic converter.
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When the MIL is illuminated and the engine stalls, the MIL will remain illuminated as long as the ignition is ON.
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When the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition is cycled OFF and then ON.
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/or 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 MAF sensor
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The IAT sensor
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The TP sensor
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The HO2S heater circuits
