Isuzu D-Max / Isuzu Rodeo (TFR/TFS). Manual - part 881
6E–253
3.2L ENGINE DRIVEABILITY AND EMISSIONS
feed circuit through transistors or through either of the
following:
D
Output Driver Module (ODM)
060RW025
ECM Components
The ECM is designed to maintain exhaust emission levels
to government mandated standards while providing
excellent driveability and fuel efficiency. The ECM
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 ECM also controls certain
engine operations through the following:
D
Fuel injector control
D
Ignition control module
D
Evaporative emission (EVAP) purge
D
A/C clutch control
ECM Voltage Description
The ECM supplies a buffered voltage to various switches
and sensors. It can do this because resistance in the
ECM is 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
5-8840-0285-0) to assure accurate voltage readings.
The input/output devices in the ECM include
analog-to-digital converters, signal buffers, counters,
and special drivers. The ECM controls most components
with electronic switches which complete a ground circuit
when turned “ON.”
ECM Input/Outputs
Inputs – Operating Conditions Read
D
Air Conditioning “ON” or “OFF”
D
Engine Coolant Temperature
D
Crankshaft Position
D
Exhaust Oxygen Content
D
Electronic Ignition
D
Barometric Pressure
D
Battery Voltage
D
Throttle Position
D
Vehicle Speed
D
Fuel Pump Voltage
D
Power Steering Pressure
D
Intake Air Temperature
D
Mass Air Flow
D
Camshaft Position
Outputs – Systems Controlled
D
EVAP Canister Purge
D
Ignition Control
D
Fuel Control
D
Idle Air Control
D
Electric Fuel Pump
D
Air Conditioning
D
Diagnostics
–
Malfunction Indicator Lamp (Service Engine
Soon lamp)
–
Data Link Connector (DLC)
–
Data Output
ECM Service Precautions
The ECM is designed to withstand normal current draws
associated with vehicle operation. Avoid overloading any
circuit. When testing for opens and shorts, do not ground
or apply voltage to any of the ECM’s circuits unless
instructed to do so. These circuits should only be tested
using digital voltmeter 5-8840-0285-0. The ECM should
remain connected to the ECM or to a recommended
breakout box.
Throttle Position (TP) Sensor
The throttle position (TP) sensor is a potentiometer
connected to the throttle shaft on the throttle body. The
ECM monitors the voltage on the signal line and
calculates throttle position. As the throttle valve angle is
changed (accelerator pedal moved), the TP sensor signal
also changes. At a closed throttle position, the output of
the TP sensor is low. As the throttle valve opens, the
output increases so that at wide open throttle (WOT), the
output voltage should be above 4 volts.
The ECM calculates fuel delivery based on throttle valve
angle (driver demand). A broken or loose TP sensor may
cause intermittent bursts of fuel from an injector and
unstable idle because the ECM thinks the throttle is
moving. A hard failure in the TP sensor 5-volt reference
or signal circuits will set either a DTC P0122 or DTC
P0123. A hard failure with the TP sensor ground circuit
may set DTC P0123 and DTC P0112. Once a DTC is set,
the ECM will use an artificial default value based on
engine RPM and mass air flow for the throttle position,
and some vehicle performance will return. A high idle
may result when either DTC P0122 or DTC P0123 is set.
The ECM can detect intermittent TP sensor faults. The
ECM can also detect a shifted TP sensor. The ECM
monitors throttle position and compares the actual TP