Isuzu engine C22NE / 22LE / 20LE. Service manual — part 88
DRIVEABILITY AND EMISSIONS 6E1-181
HOT AT ALL TIMES
Ignition
Coil
Fuse
15A
I/P
FUSE
BLOCK
Engine
Control
Module
(ECM)
E1
HOT AT ALL TIMES
ECM
Fuse
15A
U/H
FUSE
BLOCK
1.25
RED/
WHT
1.25
L
1.25
BLK
1.25
G
1.25
BLK
2
W/G
1.25
RED/
WHT
A4
A5
Batt+
Ignition
Coil
A13
0.5
G/W
E3
E2
E4
Ignition Feeds
1,4
2,3
Relay
Fuel
Pump
ECM
Fuse
15A
F/Pump
Fuse
20A
M
DIAGNOSTIC TROUBLE CODE (DTC) (Flash DTC = 49)
SYSTEM VOLTAGE HIGH
Circuit Description
The engine control module (ECM) monitors the
system voltage on the ignition feed terminal to the
ECM. A system voltage Diagnostic Trouble Code will
set whenever the voltage is above a calibrated value.
This malfunction detects an over-voltage condition in
the battery voltage circuit.
Conditions for Setting the DTC
• Engine is running.
• Battery Voltage is greater than 17.2V.
Action Taken When the DTC Sets
• The ECM will illuminate the malfunction indicator
lamp (MIL) for the first time the malfunction 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 a faulty charging system components.
6E1-182 DRIVEABILITY AND EMISSIONS
DTC (Flash DTC = 49)
System Voltage High
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
1. Ignition OFF, engine OFF.
2. Using a Digital Voltmeter (DVM), measure the battery
voltage at the battery.
Is the battery voltage greater than the specified value?
16V
Go to Step 3
Go to Step 4.
3
1. Charge the battery and clean the battery terminals.
2. Clean the battery ground cable connection if corrosion
is indicated.
Is the battery voltage greater than the specified value?
16V
Replace battery
Go to Step 4
4
1. Turn OFF all the accessories.
2. Install the Scan Tool.
3. Select the ignition voltage parameter on the data list.
4. Start the engine and raise the engine speed to 2000
RPM.
Is it the voltage above the specified value?
16V
Go to Step 5
Go to Step 6
5
Replace or repair the generator (see Charging System).
Is a malfunction present?
-
Verify Repair
-
6
Replace the EPROM or ECM.
Is the action complete?
Note) Refer to 6E1-243.
-
Verify Repair
-
DRIVEABILITY AND EMISSIONS 6E1-183
0.5
G
0.5
GR
0.5
R
0.5
G
0.5
YEL/
GRN
Engine
Control
Module
(ECM)
A3
F10
B2
B7
IAT
Sensor
Input
Sensor
Ground
Intake Air
Temperature
(IAT)
Sensor
A
B
MAP
Sensor
DIAGNOSTIC TROUBLE CODE (DTC) (Flash DTC = 69)
INTAKE AIR TEMPERATURE (IAT) SENSOR TOO HIGH
Circuit Description
The intake air temperature (IAT) sensor is a thermistor
which measures the temperature of the air entering
the engine. The engine control module (ECM) applies
5 volts through a pull-up resistor to the IAT sensor.
When the intake air is cold, the sensor resistance is
high and the ECM will monitor a high signal voltage on
the IAT signal circuit. If the intake air is warm, the
sensor resistance is lower, causing the ECM to
monitor a lower voltage. Diagnostic Trouble Code 69
will set when the ECM detects an excessively high
signal voltage on the intake air temperature sensor
signal circuit.
Conditions for Setting the DTC
• The engine is running.
• IAT sensor temperature is greater than 140 degC.
The above conditions are met.
Action Taken When the DTC Sets
• The ECM will illuminate the malfunction indicator
lamp (MIL) the first time the fault is detected.
• The ECM will use a default IAT value based on
ECM inputs and engine run time.
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 ECM - Inspect harness
connectors for backed-out terminals, improper
6E1-184 DRIVEABILITY AND EMISSIONS
mating, broken locks, improperly formed or
damaged terminals, and poor terminal-to-wire
connection.
• Damaged harness - Inspect the wiring harness for
damage, shorts to Ground, shorts to Battery
Positive, and Open Circuits. If the harness appears
to be OK, observe the IAT display on the Scan Tool
while moving connectors and wiring harnesses
related to the IAT sensor. A change in the IAT
display will indicate the location of the fault.
If Diagnostic Trouble Code 69 cannot be duplicated,
the information included in the Failure Records data
can be useful in determining vehicle mileage since the
Diagnostic Trouble Code was last set.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
2. Verifies that the fault is present.
3. If Diagnostic Trouble Code 69 can be repeated
only by duplicating the Failure Records conditions,
refer to the "Temperature vs. Resistance Values"
table. The table may be used to test the IAT sensor
at various temperatures to evaluate the possibility
of a "shifted" sensor that may be open above or
below a certain temperature. If this is the case,
replace the IAT sensor. If the IAT sensor appears
to be OK, the fault is intermittent; refer to
Diagnostic Aids.
Intake Air Temperature Sensor
°C
°F
OHMS
Temperature vs. Resistance Values
(approximate)
100
212
177
80
176
332
60
140
667
45
113
1188
35
95
1802
25
77
2796
15
59
4450
5
41
7280
−5
23
12300
−15
5
21450
−30
−22
52700
−40
−40
100700
DTC (Flash DTC = 69)
Intake Air Temperature (IAT) Sensor Too High
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
Ignition ON, engine OFF Observe the "Intake Air Temp"
values displayed on the Scan Tool.
Is the "Intake Air Temp" values below the specified value?
5V
−36°C
(
−32.8°F)
Go to Step 4
Go to Step 3
3
1. Ignition ON, engine OFF.
2. Using a Scan Tool, monitor info for Diagnostic Trouble
Code 69.
Does the Scan Tool indicate Diagnostic Trouble Code 69
failed?
-
Refer to Test
Description
Refer to
Diagnostic
Aids
4
1. Ignition OFF.
2. Disconnect the IAT sensor electrical connector.
3. Jumper the IAT signal circuit and the sensor ground
circuit together at the IAT sensor harness connector.
4. Ignition ON.
5. Observe the "Intake Air Temp" values displayed on the
Scan Tool.
Is the "Intake Air Tempe" values at the specified value?
0V
140°C
(284°F)
Go to Step 6
Go to Step 5
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