Rodeo S 2WD L4-2.2L (1999)
Engine Control Module: Description and Operation
Powertrain Control Module (PCM)
The powertrain control module (PCM) is located in the passenger compartment below the center console. The PCM controls the following:
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Fuel metering system.
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Ignition timing.
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On-board diagnostics for powertrain functions.
The PCM constantly observes the information from various sensors. The PCM controls the systems that affect vehicle performance. The PCM performs
the diagnostic function of the system. It can recognize operational problems, alert the driver through the Check Engine lamp, and store diagnostic trouble
codes (DTCs). DTCs identify the problem areas to aid the technician in making repairs.
PCM Components
The PCM is designed to maintain exhaust emission levels to government mandated standards while providing excellent driveability and fuel efficiency.
The PCM monitors numerous engine and vehicle functions via electronic sensors such as the throttle position (TP) sensor, heated oxygen sensor (HO2S),
and vehicle speed sensor (VSS). The PCM also controls certain engine operations through the following:
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Fuel injector control
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Ignition control module
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Evaporative emission (EVAP) purge
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A/C clutch control
PCM Function
The PCM supplies either 5 or 12 volts to power various sensors or switches. The power is supplied through resistances in the PCM which are so high in
value that a test light will not light when connected to the circuit. In some cases, even an ordinary shop voltmeter will not give an accurate reading
because its resistance is too low. Therefore, a digital voltmeter with at least 10 megohms input impedance is required to ensure accurate voltage
readings. Tool J 39200 meets this requirement. The PCM controls output circuits such as the injectors, IAC, cooling fan relays, etc., by controlling the
ground or the power feed circuit through transistors or through either of the following two devices:
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Output Driver Module (ODM)
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Quad Driver Module (QDM)
PCM Voltage Description
The PCM supplies a buffered voltage to various switches and sensors. It can do this because resistors in the PCM which are so high in value that a test
light may not illuminate when connected to the circuit. An ordinary shop voltmeter may not give an accurate reading because the voltmeter input
impedance is too low. Use a 10-megohm input impedance digital voltmeter (such as J 39200) to assure accurate voltage readings.
