Isuzu engine C22NE / 22LE / 20LE. Service manual — part 115

DRIVEABILITY AND EMISSIONS 6E1-289

ECM INPUTS/OUTPUTS

Inputs - Operating Conditions Read

• Air Conditioning Compressor Clutch ON or OFF
• Engine Coolant Temperature
• Crankshaft Position
• Exhaust Oxygen Content (If equipped)
• Manifold Absolute Pressure
• Battery Voltage
• Throttle Position
• Knock
• Vehicle Speed
• Fuel Pump Voltage
• Power Steering Pressure
• Intake Air Temperature

Outputs - Systems Controlled

• EVAP Canister Purge Control Solenoid Valve
• Ignition Control
• Fuel Injector Control
• Idle Air Control
• Electric Fuel Pump Relay
• Air Conditioning Compressor Clutch Relay
• Diagnostics

- OBD Malfunction Indicator Lamp (Check Engine lamp)

- Data Link Connector (DLC)

- Data

Output

•Tachometer Signal

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 5-8840-2392-0. The ECM should remain connected
to the ECM or to a recommended breakout box.

6E1-290 DRIVEABILITY AND EMISSIONS

THROTTLE POSITION SENSOR (TPS)

The throttle position sensor (TPS) 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 TPS signal also changes. At a closed
throttle position, the output of the TPS is about 0.25 Volts. As
the throttle valve opens, the output increases so that at wide
open throttle (WOT), the output voltage should be about 4.75
volts.
The ECM calculates fuel delivery based on throttle valve angle
and manifold pressure for fuel delivery under the most
circumstances. A broken or loose TPS 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 TPS 5-
volt reference or signal circuits will set either a DTC21 or 22. If
ECM detects a low impedance short to ground in the TPS
circuit, Diagnostic Trouble code 22 will be set.
If ECM detects a low impedance short to battery in the TPS
circuit, Diagnostic Trouble Code 21 will be set.

VEHICLE SPEED SENSOR (VSS)

The ECM determines the speed of the vehicle by converting a
pulsing voltage signal from the vehicle speed sensor (VSS) into
km per hour. The ECM uses this signal to operate the
speedometer.

USE OF CIRCUIT TESTING TOOLS

Do not use a test light to diagnose the electic electrical system
unless specifically instructed by the diagnostic procedures. Use
Connector Test Adapter Kit 5-8840-0385-0 whenever
diagnostic procedures call for probing connectors.

DRIVEABILITY AND EMISSIONS 6E1-291

AFTERMARKET ELECTRICAL AND VACUUM

EQUIPMENT

Aftermarket (add-on) electrical and vacuum equipment is
defined as any equipment which connects to the vehicle's
electrical or vacuum systems that is installed on a vehicle after
it leaves the factory. No allowances have been made in the
vehicle design for this type of equipment.
Notice: No add-on vacuum equipment should be added to this
vehicle.
Notice: Add-on electrical equipment must only be connected to
the vehicle's electrical system at the battery (power and
ground).
Add-on electrical equipment, even when installed to these
guidelines, may still cause the electric system to malfunction.
This may also include equipment not connected to the vehicle
electrical system such as portable telephones and radios.
Therefore, the first step in diagnosing any electric problem is to
eliminate all aftermarket electrical equipment from the vehicle.
After this is done, if the problem still exists, it may be
diagnosed in the normal manner.

ELECTROSTATIC DISCHARGE DAMAGE

Electronic components used in the ECM are often designed to
carry very low voltage. Electronic components are susceptible
to damage caused by electrostatic discharge. Less than 100
volts of static electricity can cause damage to some electronic
components. By comparison, it takes as much as 4000 volts
for a person to feel even the zap of a static discharge.
There are several ways for a person to become statically
charged. The most common methods of charging are by
friction and induction.
• An example of charging by friction is a person sliding across

a vehicle seat.

• Charge by induction occurs when a person with well-

insulated shoes stands near a highly charged object and

momentarily touches ground. Charges of the same polarity

are drained off leaving the person highly charged with the

opposite polarity. Static charges can cause damage,

therefore it is important to use care when handling and

testing electronic components.

6E1-292 DRIVEABILITY AND EMISSIONS

Notice: To prevent possible electrostatic discharge damage,
follow these guidelines:
• Do not touch the ECM connector pins or soldered

components on the ECM circuit board.

• Do not touch any electronic module component leads.
• Do not open the replacement part package until the part is

ready to be installed.

• Before removing the part from the package, ground the

package to a known good ground on the vehicle.

• If the part has been handled while sliding across the seat,

while sitting down from a standing position, or while walking

a distance, touch a known good ground before installing the

part.

AIR INDUCTION

AIR INDUCTION SYSTEM

The air induction system filters contaminants from the outside air,
and directs the progress of the air as it is drawn into the engine. A
remote-mounted air cleaner prevents dirt and debris in the air from
entering the engine. The air duct assembly routes filtered air to the
throttle body. Air enters the engine by the following steps:
1. Through the throttle body.

2. Into the intake manifold.

3. Through the cylinder head intake ports.

4. Into the cylinders.

FUEL METERING

ACCELERATION MODE

The ECM provides extra fuel when it detects a rapid increase in
the throttle position and the air flow.

ACCELERATOR CONTROLS

the accelerator control system is a cable-type system with
specific linkage adjustments.
Refer to Cable Adjustment.