Isuzu engine C22NE / 22LE / 20LE. Service manual — part 93
DRIVEABILITY AND EMISSIONS 6E1-201
HOT IN START AND RUN
IG.
Coil
Fuse
15A
I/P
FUSE
BLOCK
2
W/G
Ignition
Coil
Ignition
Coil
1.25
G
1.25
L
Engine
Control
Module
(ECM)
E1
E4
E3
Electronic Spark
Timing Control
1.25
BLK
1.25
BLK
E2
1,4
2,3
DIAGNOSTIC TROUBLE CODE (DTC) (Flash DTC = 64)
IGNITION COIL DRIVER "A" SHORT TO GROUND
Circuit Description
The ignition control circuit in ECM provides a zero volt
or a 5 volt signal to the ignition coil driver. The normal
circuit voltage is zero volts. When the coil driver
receives the 5 volt signal from the ignition control
circuit, it provides a ground path for the B+ voltage
supplied to the ignition primary coil. When the ECM
turns off the 5 volts to the module, the module will
remove the ground path of the ignition primary coils;
causing the magnetic field produces a voltage in the
secondary coils which fires the spark plug.
The circuit between the coil driver and the ignition
control circuit is monitored for a short to ground on the
Electronic Spark Timing A/coil drive A line. When the
ECM detects a problem in the ignition control circuit, it
will set DTC 64.
Conditions for Setting the DTC
• Fault feedback line generates an interrupt on end of
dwell.
• No Electronic Spark Timing activation requested by
serial data.
Action Taken When the DTC Sets
• The ECM will illuminate the malfunction indicator
lamp (MIL) the first time the fault is detected.
Conditions for Clearing the MIL/DTC
Once the ECM determines that a fault(s) has been
rectified then the CEL 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.
Diagnostic Aids
Check for the following conditions:
• Poor connection at the ECM - Inspect the harness
connectors for backed-out terminals, improper
mating, broken locks, improperly formed or
6E1-202 DRIVEABILITY AND EMISSIONS
damaged terminals, and poor terminal-to-wire
connections.
• Damaged harness - Inspect the wiring harness for
damage; Open circuits, shorts to ground, or shorts
to Voltage. If the harness appears to be OK,
observe the Scan Tool display related to DTC 64
while moving the connector and wiring related to the
ignition system. A change in the display will indicate
the location of the fault.
• This code detects a short to ground on the
Electronic Spark Timing A/Coil Driver A (#1, #4 cyl.)
line.
DTC (Flash DTC = 64)
Ignition Coil Driver "A" Short To Ground
Step
Action
Value(s)
Yes
No
1
Was the "On-Board Diagnostic (OBD) System Check"
performed?
-
Go to Step 2
Go to OBD
System
Check
2
Check for a faulty connection or damaged terminals at the
ignition control module.
Was a problem found?
-
Verify repair
Go to Step 3
3
Check for a faulty connection or damaged terminals at the
ECM connector.
Was a problem found?
-
Verify repair
Go to Step 4
4
Check for a open circuit between the ignition coil and
ECM.
If a problem is found, repair the wire harness.
Is there still a problem?
-
Verify repair
Go to Step 5
5
Check for a short to ground between the ignition coil and
battery +.
If a problem is found, repair the wire harness.
Is there still a problem?
-
Verify repair
Go to Step 6
6
1. Ignition OFF.
2. Disconnect the ignition coil.
3. Check the ignition control circuit for a short to voltage.
Was a problem found?
-
Verify repair
Go to Step 7
7
Replace the ignition control module.
Verify repair.
Is there still a problem?
-
Go to Step 8
-
8
Replace the EPROM or ECM.
Is the repair complete?
Note) Refer to 6E1-243.
-
Verify repair
-
DRIVEABILITY AND EMISSIONS 6E1-203
Engine
Control
Module
(ECM)
B16
0.5
L
0.5
L/W
0.5
L/R
Idle Air
Control
(IAC)
Valve
0.5
L/B
B15
D
C
B
A
B13
B14
IAC
A
High
IAC
A
Low
IAC
B
High
IAC
B
Low
A
B
DIAGNOSTIC TROUBLE CODE (DTC) (Flash DTC = 35)
IDLE AIR CONTROL (IAC) ERROR
Circuit Description
The engine control module (ECM) controls engine idle
speed with the idle air control (IAC) valve. To increase
idle speed, the ECM retracts the IAC valve pintle away
from its seat, allowing more air to bypass the throttle
bore. To decrease idle speed, it extends the IAC valve
pintle towards its seat, reducing bypass air flow. A
Scan Tool will read the ECM commands to the IAC
valve in counts. Higher counts indicate more air
bypass (higher idle). Lower counts indicate less air is
allowed to bypass (lower idle).
This malfunction detects an error in the IAC control
logic, then DTC 35 will set.
Conditions for setting the DTC
• Engine rpm error is greater than 175 rpm.
• No DTC 21, 22 and 24 present.
And,
• Engine desired rpm is not fixed by tester.
• IAC movement is not inhibited by low or high battery
voltage.
And,
• IAC normal closed loop is enabled.
• Coolant of lesets are decayed to 0.
6E1-204 DRIVEABILITY AND EMISSIONS
Action Taken when the DTC sets
• The ECM will illuminate the malfunction indicator
lamp (MIL).
Conditions for Clearing the MIL/DTC
Once the ECM determines that a fault(s) has been
rectified then the CEL 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.
Diagnostic Aids
A slow, unstable, or fast idle may be caused by a non-
IAC system problem that cannot be overcome by the
IAC valve. Out of control range IAC Scan Tool counts
will be above 60 if idle is too low, and zero counts if
idle is too high. The following checks should be made
to repair a non-IAC system problem:
• Vacuum leak (high idle) - If idle is too high, stop the
engine. Fully extend (low) IAC with the IAC motor
analyzer 5-8840-2312-0. Start the engine. If idle
speed is above 825 RPM, locate and correct the
vacuum leak, including the PCV system. Check for
binding of the throttle blade or linkage.
Following are applicable to the vehicle with
closed Loop System.
• Throttle body - Remove the IAC valve and inspect
the bore for foreign material.
• IAC valve electrical connections - IAC valve
connections should be carefully checked for proper
contact.
• PCV hose - An incorrect or faulty hose may result in
an incorrect idle speed. Refer to Diagnosis, Rough
Idle, Stalling. If intermittent poor driveability or idle
symptoms are resolved by disconnecting the IAC,
carefully recheck the connections and valve
terminal resistance, or replace the IAC.
• Lean heated oxygen sensor signal (high air/fuel
ratio) - The idle speed may be too high or too low.
Engine speed may vary up and down, and
disconnecting the IAC valve does not help.
Diagnostic trouble code 44 may be set. Scan Tool
oxygen (O2) voltage will be less than 27 mV (2.74
V). Check for low regulated fuel pressure, waterin
fuel, or a restricted injector.
• Rich heated oxygen sensor signal (low air/fuel ratio)
- The idle speed will be too low. Scan Tool IAC
counts will usually be above 80. The system is
obviously rich and may exhibit black smoke in the
exhaust.
• Scan Tool O2 voltage will be fixed at about 750 mV
(0.75 V). Check for high fuel pressure, or a leaking
or sticking injector. A silicon-contaminated heated
oxygen sensor will show an O2 voltage slow to
respond on the Scan Tool.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
1. The IAC motor analyzer 5-8840-2312-0 is used to
extend and retract the IAC valve. Valve movement
is verified by an engine speed change. If no
change in engine speed occurs, the valve can be
resettled when removed from the throttle body.
2. This step checks the quality of the IAC movement
in step 1. Between 700 revolutions per minute
(RPM) and about 1500 RPM, the engine speed
should change smoothly with each flash of the
tester light in both extend and retract. If the IAC
valve is retracted beyond the control range (about
1500 RPM), it may take many flashes to extend the
IAC valve before engine speed will begin to drop.
This is normal on certain engines. Fully extending
the IAC may cause engine stall. This may be
normal.
6. Steps 1 and 2 verified the proper IAC valve
operation. This step checks the IAC circuits. Each
lamp on the noid light should flash red and green
while the IAC valve is cycled. While the sequence
of color is not important, if either light is OFF or
does not flash red and green, check the circuits for
faults, beginning with poor terminal contacts.
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