Isuzu engine C22NE / 22LE / 20LE. Service manual — part 54

DRIVEABILITY AND EMISSIONS 6E1-45

BASIC KNOWLEDGE OF TOOLS

REQUIRED

Notice: Lack of basic knowledge of this powertrain

when performing diagnostic procedures could result in

an incorrect diagnosis or damage to powertrain

components. Do not attempt to diagnose a powertrain

problem without this basic knowledge.

A basic understanding of hand tools is necessary to

effectively use this section of the Service Manual.

SERIAL DATA COMMUNICATIONS

This vehicle utilizes the serial data communication

system. Each bit of information can have one of two

lengths: long or short. This allows vehicle wiring to be

reduced by transmitting and receiving multiple signals

over a single wire. The messages carried on serial

data streams are also prioritized. If two messages

attempt to establish communications on the data line

at the same time, only the message with higher priority

will continue. The device with the lower priority

message must wait. For more information on this

system of coding, refer to Decimal/ Binary/

Hexadecimal Conversions. On this vehicle the Scan

Tool displays the actual values for vehicle parameters.

It will not be necessary to perform any conversions

from coded values to actual values.

ON-BOARD

DIAGNOSTIC (OBD)

ON-BOARD DIAGNOSTIC TESTS

Miscellaneous Test:

A miscellaneous test is a kind of the On-Board

Diagnostics.

Using a tech 2, the miscellaneous test can be

conducted, followings are brief description about the

miscellaneous tests.

To perform the miscellaneous test, allows the

displayed menu on the tech 2. Sub-menu of

miscellaneous test are as follows.

• Check powertrain lamp:

This test allows to turn on and off the powertrain

warning lamp in the instrument cluster.

• Fuel Pump:

Fuel pump test allows to turn on and off the fuel

pump.

If turned off while the engine is running, the engine

will stall.

• A/C Clutch:

The A/C Clutch test allows to turn on and off the

airconditioning.

• Canister Purge Control Solenoid Valve:

This function takes control of the canister purge

control solenoid valve.

The on command represents a 100% pwm, the off

command a 0% pwm.

• IAC (Idle Air Control) System:

• RPM control

This function allows the user to slew the desired

RPM via increments of 25 RPM with a minimum

of 600 RPM and a maximum of 2000 RPM.

The start value will be at 1150 RPM.

• IAC Control

This function allows the user to slew the IAC via

increments of 25 steps with a minimum of 0 steps

and a maximum of 250 steps.

The start value will be at idle steps.

• IAC Reset

The user will have the ability to perform an IAC

reset.

Each keypress will actuate the command to reset.

• Fuel Trim Reset:

This function allows the user to command the ECM

to perform an Long Term Fuel Trim reset, also

known as a Block Learn Memory reset.

Each keypress will actuate the command to reset.

• Fueling Mode:

This function provides the user with the ability to

enable or disable closed loop fuel control.

• Air Fuel Ratio:

This function allows the user to slew the control

state of the A/F ratio within a minimum of 11.7:1

and a maximum of 17.7:1.

The test starts at an A/F ratio of 14.7 : 1.

The incremental control is 0.5 steps per keypress.

COMPREHENSIVE COMPONENT

MONITOR DIAGNOSTIC OPERATION

Comprehensive component monitoring diagnostics

are involved to monitor emissions-related input and

output engine components.

6E1-46 DRIVEABILITY AND EMISSIONS

Input Components:

Input components are monitored for circuit continuity

and out-of-range values. This includes rationality

checking. Rationality checking refers to indicating a

fault when the signal from a sensor does not seem

reasonable, i.e. Throttle Position (TP) sensor that

indicates high throttle position at low engine loads or

MAP voltage). Input components may include, but are

not limited to the following sensors:
• Vehicle Speed Sensor (VSS)
• Crankshaft Position (CKP) sensor
• Throttle Position (TP) sensor
• Engine Coolant Temperature (ECT) sensor
• Intake Air Temperature Sensor (IAT)
• Manifold Absolute Pressure (MAP) sensor
In addition to the circuit continuity and rationality check

the ECT sensor is monitored for its ability to achieve a

steady state temperature to enable “Closed Loop” fuel

control (If applicable).

Output Components:

Output components are diagnosed for proper

response to control module commands. Components

where functional monitoring is not feasible will be

monitored for circuit continuity and out-of-range values

if applicable.

Output components to be monitored include, but are

not limited to the following circuit:
• Idle Air Control (IAC) Motor
• EVAP Canister Purge Valve Solenoid
• A/C relays
• VSS output
• MIL control
Refer to ECM and Sensors in General Descriptions.

Passive and Active Diagnostic Tests

A passive test is a diagnostic test which simply

monitors a vehicle system or component. Conversely,

an active test, actually takes some sort of action when

performing diagnostic functions, often in response to a

failed passive test.

Intrusive Diagnostic Tests

This is any on-board test run by the Diagnostic

Management System which may have an effect on

vehicle performance or emission levels.

Warm-Up Cycle

A warm-up cycle means that engine at temperature

must reach a minimum of 70°C(160°F) and rise at

least 22°C(40°F) over the course of a trip.

COMMON OBD TERMS

Diagnostic For Closed Loop System:

When used as a noun, the word diagnostic refers to

any on-board test run by the vehicle's Diagnostic

Management System. A diagnostic is simply a test run

on a system or component to determine if the system

or component is operating according to specification.

For Closed Loop System:

There are many diagnostics, shown in the following

list:
• Oxygen sensors
• Oxygen sensor heaters

Enable Criteria

The term “enable criteria” is engineering language for

the conditions necessary for a given diagnostic test to

run. Each diagnostic has a specific list of conditions

which must be met before the diagnostic will run.

“Enable criteria” is another way of saying “conditions

required” .

The enable criteria for each diagnostic is listed on the

first page of the DTC description under the heading

“Conditions for Setting the DTC” . Enable criteria

varies with each diagnostic, and typically includes, but

is not limited to the following items:
• engine speed
• vehicle speed
• ECT
• MAP
• IAT
• TP
• high canister purge (If applicable)
• A/C ON

Trip

Technically, a trip is a key on-run-key off cycle in

which all the enable criteria for a given diagnostic are

met, allowing the diagnostic to run. Unfortunately, this

concept is not quite that simple. A trip is official when

all the enable criteria for a given diagnostic are met.

But because the enable criteria vary from one

diagnostic to another, the definition of trip varies as

well. Some diagnostics are run when the vehicle is at

operating temperature, some when the vehicle first

start up; some require that the vehicle be cruising at a

steady highway speed, some run only when the

vehicle is at idle. Some run only immediately following

a cold engine start-up.

A trip then, is defined as a key on-run-key off cycle in

which the vehicle was operated in such a way as to

DRIVEABILITY AND EMISSIONS 6E1-47

satisfy the enabled criteria for a given diagnostic, and

this diagnostic will consider this cycle to be one trip.

However, another diagnostic with a different set of

enable criteria (which were not met) during this driving

event, would not consider it a trip. No trip will occur for

that particular diagnostic until the vehicle is driven in

such a way as to meet al the enable criteria

THE DIAGNOSTIC EXECUTIVE

The Diagnostic Executive is a unique segment of

software which is designed to coordinate and prioritize

the diagnostic procedures as well as define the

protocol for recording and displaying their results. The

main responsibilities of the Diagnostic Executive are

listed as follows:
• Commanding the MIL(“Check Engine” lamp) ON

and OFF

• DTC logging and clearing
• Current status information ON each diagnostic
The Diagnostic Executive records DTCs and turns ON

the MIL when emission-related faults occur. It can also

turn OFF the MIL if the conditions cease which caused

the DTC to set.

Diagnostic Information

The diagnostic charts and functional checks are

designed to locate a faulty circuit or component

through a process of logical decisions. The charts are

prepared with the requirement that the vehicle

functioned correctly at the time of assembly and that

there are not multiple faults present.

There is a continuous self-diagnosis on certain control

functions. This diagnostic capability is complimented

by the diagnostic procedures contained in this manual.

The language of communicating the source of the

malfunction is a system of diagnostic trouble codes.

When a malfunction is detected by the control module,

a diagnostic trouble code is set and the Malfunction

Indicator Lamp (MIL)(“Check Engine” lamp) is

illuminated.

Malfunction Indicator Lamp (MIL)

The Malfunction Indicator Lamp (MIL) looks the same

as the MIL you are already familiar with (“Check

Engine” lamp).

Basically, the MIL is turned ON when the ECM detects

a DTC.

Extinguishing the MIL

The MIL (“Check Engine” lamp) is on the instrument

panel and has the following functions:

• It informs the driver that a fault that affects vehicle

emission levels has occurred and that the vehicle

should be taken for service as soon as possible.

• As a bulb and system check, the MIL will come on

with the key on and the engine not running. When

the engine is started, the MIL will turn OFF.

• When the MIL remains on while the engine is

running, or when a malfunction is suspected due to

a driveability or emissions problem, a Powertrain

On-Board Diagnostic (OBD) System Check must be

performed. The procedures for these checks are

given in On-Board Diagnostic (OBD) System

Check. These checks will expose faults which may

not be detected if other diagnostics are performed

first.

Once the ECM determines that a fault(s) has been

rectified then the MIL will switch OFF, although the

fault code will remain in the ECM memory.

Any fault codes will remain in ECM memory until -

1. They are cleared by disconnecting the Battery for

more than 30 seconds.

2. A service tool such as Tech 2 is used to clear them.

3. Ten consecutive starts without logging a fault.

Refer to clearing Diagmostic Trouble Code

Data Link Connector (DLC)

The Provision for communicating with the control

module is the Data Link Connector (DLC). It is located

at the lower left of the instrument panel behind a small

square cover. The DLC is used to connect to a Scan

Tool. Some common uses of the Scan Tool are listed

below:
• Identifying stored Diagnostic Trouble Codes (DTCs)
• Clearing DTCs
• Performing output control tests
• Reading serial data

6E1-48 DRIVEABILITY AND EMISSIONS

Reading Flash Diagnostic Trouble Codes

The provision for communicating with the Engine

Control Module (ECM) is the Data Link Connector

(DLC). The DLC is located behind the lower front

instrument panel. It is used in the assembly plant to

receive information in checking that the engine is

operating properly before it leaves the plant.

The diagnostic trouble code(s) (DTCs) stored in the

ECM’s memory can be read either through a hand-

held diagnostic scanner plugged into the DLC or by

counting the number of flashes of the ”Check Engine”

Malfunction lndicator Lamp (MIL) when the diagnostic

test terminal of the DLC is grounded. The DLC

terminal ”6” (diagnostic request) is pulled ”Low”

(grounded) by jumpering to DLC terminal ”5”, Which is

a ground wire.

This will signal the ECM that you want to ”flash”

DTC(s), if any are present. Once terminals ”5” and ”6”

have been connected, the ignition switch must be

moved to the ”ON” position, with the engine not

running. At this point, the ”Check Engine” MIL should

flash DTC12 three times consecutively.

This would be the following flash, sequence: ”flash,

pause, flash-flash, long pause, flash, pause, flash-

flash, long pause, flash, pause, flash-flash”. DTC12

indicates that the ECM’s diagnostic system is

operating. If DTC12 is not indicated, a problem is

present within the diagnostic system itself, and should

be addressed by consulting the appropriate diagnostic

chart in DRIVEABILITY AND EMISSIONS.

Following the output of DTC12, the ”Check Engine”

MIL will indicate a DTC three times if a DTC is

present, or it will simply continue to output DTC12. If

more than one DTC three has been stored in the

ECM’s memory, the DTC(s) will be output from the

lowest to the highest, with each DTC being displayed

three times.

Reading Diagnostic Trouble Codes Using

a TECH 2

The procedure for reading diagnostic trouble code(s)

is to used a diagnostic Tech 2. When reading DTC(s),

follow instructions supplied by Tech 2 manufacturer.

Clearing Diagnostic Trouble Codes

IMPORTANT: Do not clear DTCs unless directed to

do so by the service information provided for each

diagnostic procedure.

If the fault that caused the DTC to be stored into

memory has been corrected, the Diagnostic Executive

will begin to count the ”warm-up” cycles with no further

faults detected, the DTC will automatically be cleared

from the ECM memory.

To clear Diagnostic Trouble Codes (DTCs), use the

Tech 2 ”clear DTCs” or ”clear information” function.

When clearing DTCs follow instructions supplied by

the Tech 2 manufacturer.

When a Tech 2 is not available, DTCs can also be

cleared by disconnecting one of the following sources

for at least thirty (30) seconds.

NOTE: To prevent system damage, the ignition key

must be ”OFF” when disconnecting or reconnecting

battery power.
• The power source to the control module. Examples:

fuse, pigtail at battery ECM connectors etc.

• The negative battery cable. (Disconnecting the

negative battery cable will result in the loss of other

on-board memory data, such as preset radio

tuning).