Powertrain Control Module (Pcm); Pcm Function; Pcm Components; Pcm Voltage Description - Isuzu 1999 RODEO Workshop Manual

6E1–428 RODEO X22SE 2.2L ENGINE DRIVEABILITY AND EMISSION

Powertrain Control Module (PCM)

The powertrain control module (PCM) is located in the
passenger compartment below the center console. The
PCM controls the following:
f Fuel metering system.
f Ignition timing.
f 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 Function

The PCM supplies either 5 or 12 volts to power various
sensors or switches. The power is supplied through
resistors 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 megW 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:
f Output Driver Module (ODM)
f Quad Driver Module (QDM)

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
014RX013
speed sensor (VSS). The PCM also controls certain
engine operations through the following:
f Fuel injector control
f Ignition control module
f Evaporative emission (EVAP) purge
f A/C clutch control

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.
The input/output
analog–to–digital converters, signal buffers, counters,
and special drivers. The PCM controls most components
with electronic switches which complete a ground circuit
when turned ON. These switches are arranged in groups
of 4 and 7, called either a quad driver module (QDM),
which can independently control up to 4 output terminals,
or Output Driver Module (ODM) which can independently
control up to 7 outputs. Not all outputs are always used.

PCM Inputs/Outputs

Inputs – Operating Conditions Read
f Air Conditioning Compressor Clutch ON or OFF
f Engine Coolant Temperature
f Crankshaft Position
f Exhaust Oxygen Content
f Manifold Absolute Pressure
f Battery Voltage
014RX002
f Throttle Position
f Fuel Tank Vapor Pressure
f Fuel Tank Level
f Exhaust Gas Recirculation (EGR) Feedback
f Knock
devices in the PCM include