Isuzu engine C22NE / 22LE / 20LE. Service manual — part 56
DRIVEABILITY AND EMISSIONS 6E1-53
VERIFYING VEHICLE REPAIR
Verification of vehicle repair will be more
comprehensive for vehicles with OBD system
diagnostics. Following a repair, the technician should
perform the following steps:
1. Review and record the customer complaint for the
DTC which has been diagnosed.
2. Clear DTC(s).
3. Operate the vehicle within conditions noted in the
customer complaint.
4. Monitor the DTC status information for the specific
DTC which has been diagnosed until the diagnostic
test associated with that DTC runs.
Following these steps are very important in verifying
repairs on OBD systems. Failure to follow these steps
could result in unnecessary repairs.
READING DIAGNOSTIC TROUBLE
CODES USING A SCAN TOOL
The procedure for reading diagnostic trouble code(s)
is to use a diagnostic Scan Tool. When reading
DTC(s), follow instructions supplied by tool
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
form the ECM memory.
To clear Diagnostic Trouble Codes (DTCs), use the
diagnostic Scan Tool “clear DTCs” or “clear
information” function. When clearing DTCs follow
instructions supplied by the tool manufacturer.
When a Scan Tool is not available, DTCs can also be
cleared by disconnecting one of the following sources
for at least thirty (30) seconds.
Notice: 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).
6E1-54 DRIVEABILITY AND EMISSIONS
DTC MODES
There are 2 options available in the Scan Tool DTC
mode to display the enhanced information available.
After selecting DTC, the following menu appears:
• DTC Info
• Clear DTC Info
The following is a brief description of each of the sub
menus in DTC Info and Specific DTC. The order in
which they appear here is alphabetical and not
necessarily the way they will appear on the Scan Tool.
DTC Information Mode
Use the DTC info mode to search for a stored DTC
Refer to “Diagnostic Trouble Codes” list.
Clear DTC Information
The command for clearing DTC’s performs a
complete reset of the ECM.
PRIMARY SYSTEM-BASED
DIAGNOSTICS
PRIMARY SYSTEM-BASED
DIAGNOSTICS
There are primary system-based diagnostics which
evaluate system operation and its effect on vehicle
emissions. The primary system-based diagnostics are
listed below with a brief description of the diagnostic
function:
FUEL CONTROL HEATED OXYGEN
SENSORS (IF APPLICABLE)
The main function of the fuel control heated oxygen
sensors is to provide the control module with exhaust
stream oxygen content information to allow proper
fueling and maintain emissions within mandated
levels. After it reaches operating temperature, the
sensor will generate a voltage, inversely proportional
to the amount of oxygen present in the exhaust gases.
The control module uses the signal voltage from the
fuel control heated oxygen sensors while in “Closed
Loop” to adjust fuel injector pulse width. While in
“Closed Loop” , the ECM can adjust fuel delivery to
maintain an air/fuel ratio which allows the best
combination of emission control and driveability. The
fuel control heated oxygen sensors are also used to
determine catalyst efficiency.
HO2S HEATER
Heated oxygen sensors are used to minimize the
amount of time required for “Closed Loop” fuel control
to begin operation and to allow accurate catalyst
monitoring. The oxygen sensor heater greatly
decreases the amount of time required for fuel control
sensor (HO2S) to become active.
DRIVEABILITY AND EMISSIONS 6E1-55
ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK
16 15 14 13 12 11 10 9
8 7 6 5 4 3 2 1
HOT AT ALL TIMES
Fuse
Stop
10A
U/H
FUSE
BLOCK
To
Stop
Lamp
Engine
Control
Module
(ECM)
0.5G
A1
B11
E8
B/R
0.5
BW
0.5
R
ECM
Grounds
(Engine Block)
Diag
Serial Data
1.25
Circuit Description
The on-board diagnostic system check is the starting
point for any driveability complaint diagnosis. Before
using this procedure, perform a careful visual/physical
check of the ECM and engine grounds for cleanliness
and tightness.
The on-board diagnostic system check is an organized
approach to identifying a problem created by an
electronic engine control system malfunction.
Diagnostic Aids
An intermittent may be caused by a poor connection,
rubbed-through wire insulation or a wire broken inside
the insulation. Check for poor connections or a
damaged harness. Inspect the ECM harness and
connectors for improper mating, broken locks,
improperly formed or damaged terminals, poor
terminal-to-wire connection, and damaged harness.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart:
1. The MIL (“Check Engine” lamp) should be ON
steady with the ignition ON/engine OFF. If not,
isolate the malfunction in the MIL circuit.
2. Checks the serial data circuit and ensures that the
ECM is able to transmit serial data.
6E1-56 DRIVEABILITY AND EMISSIONS
3. This test ensures that the ECM is capable of
controlling the MIL and the MIL driver circuit is not
shorted to ground.
4. If the engine will not start, the Cranks But Will Not
Run chart should be used to diagnose the
condition.
7. A Scan Tool parameter which is not within the
typical range may help to isolate the area which is
causing the problem.
On-Board Diagnostic (OBD) System Check
Step
Action
Value(s)
Yes
No
1
1. Ignition ON engine OFF.
2. Observe the malfunction indicator lamp (MIL or
“Check Engine” lamp).
Is the MIL (“Check Engine” lamp) ON?
-
Go to Step 2
Go to
No MIL
2
1. Ignition OFF.
2. Install a Scan Tool.
3. Ignition ON.
4. Attempt to display ECM engine data with the Scan Tool.
Does the Scan Tool display ECM data?
-
Go to Step 3
Go to Step 8
3
1. Using the Scan Tool output tests function, select MIL
dash lamp control and command the MIL OFF.
2. Observe the MIL.
Did the MIL turn OFF?
-
Go to Step 4
Go to
MIL(“Check
Engine” Lamp)
On Steady
4
Attempt to start the engine.
Did the engine start and continue to run?
-
Go to Step 5
Go to
Cranks But
Will Not Run
5
Select “Display DTCs” with the Scan Tool.
Are any DTCs stored?
-
Go to Step 6
Go to Step 7
6
Are two or more of the following DTCs stored?
• 14
• 21
• 22
• 33
• 34
• 69
-
Go to
“Multiple ECM
Information
Sensor DTCs
Set”
Go to
applicable
DTC table
7
Compare ECM data values displayed on the Scan Tool to
the typical engine scan data values.
Are the displayed values normal or close to the typical
values?
-
Go to Step 8
Refer to
indicated
Component
System Checks
8
1. Ignition OFF, disconnect the ECM.
2. Ignition ON, engine OFF.
3. Check the serial data circuit for an open, short to
ground, or short to voltage. Also, check the DLC
ignition feed circuit for an open or short to ground and
the DLC ground circuits for an open.
4. If a problem is found, repair as necessary. Was a
problem found?
-
Go to Step 2
Go to Step 9
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