Isuzu engine C22NE / 22LE / 20LE. Manual — part 89
DRIVEABILITY AND EMISSIONS 6E1-185
DTC (Flash DTC = 69)
Intake Air Temperature (IAT) Sensor Too High (cont'd)
Step
Action
Value(s)
Yes
No
5
1. Jumper the IAT signal circuit at the IAT sensor harness
connector to chassis ground.
2. Observe the "Intake Air Temp" display on the Scan
Tool.
Is the "Intake Air Tempe" at the specified value?
0V
140°C
(284°F)
Go to Step 7
Go to Step 8
6
Check for poor connections at the IAT sensor and replace
terminals if necessary.
Did any terminals require replacement?
-
Verify repair
Go to Step 10
7
1. Ignition OFF.
2. Disconnect the ECM, and check the IAT sensor ground
circuit for an open.
3. If the IAT sensor ground circuit is open, repair it as
necessary.
Was the IAT sensor ground circuit open?
-
Verify repair
Go to Step 9
8
1. Ignition OFF.
2. Disconnect the ECM, and check the IAT signal circuit
for an open.
3. If the IAT sensor signal circuit is open, repair it as
necessary.
Was the IAT signal circuit open?
-
Verify repair
Go to Step 9
9
Check for a poor sensor ground or IAT signal circuit
terminal connection at the ECM and replace terminal(s) if
necessary.
Did any of the terminal need to be replaced?
-
Verify repair
Go to Step 11
10
Replace the IAT sensor.
Is the action complete?
-
Verify repair
-
11
Replace the EPROM or ECM.
Is the action complete?
Note) Refer to 6E1-243.
-
Verify repair
-
6E1-186 DRIVEABILITY AND EMISSIONS
DRIVEABILITY AND EMISSIONS 6E1-187
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 = 71)
INTAKE AIR TEMPERATURE (IAT) SENSOR TOO LOW
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 71
will set when the ECM detects an excessively low
signal voltage (short to ground) on the intake air
temperature sensor signal circuit.
Conditions for Setting the DTC
• The engine has been running for over 2 minutes.
• IAT sensor temperature is less than −36 degC.
The above conditions are met.
Action Taken When the DTC Sets
• The ECM will illuminate the malfunction indicator
lamp (MIL).
• The ECM will use a default IAT value based on
PCM 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.
6E1-188 DRIVEABILITY AND EMISSIONS
Diagnostic Aids
Check for the following conditions:
• Poor connection at ECM - Inspect harness
connectors for backed-out terminals, improper
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, 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 71 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 71 can be repeated
only by duplicating the Failure Records condition,
refer to the Temperature vs. Resistance Value
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 stored 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 = 71)
Intake Air Temperature (IAT) Sensor Too Low
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 ON, engine OFF
2. Using a Scan Tool, monitor the intake air temperature
(IAT).
Is the intake air temperature greater then the specified
value?
140°C
(284°F)
Go to Step 4
Go to Step 3
3
1. Ignition ON, engine OFF Review and record Scan Tool
Failure Records data.
2. Using a Scan Tool, monitor the info for Diagnostic
Trouble Code 71.
Does the Scan Tool indicate Diagnostic Trouble Code 71?
-
Refer to Test
Description
Refer to
Diagnostic
Aids
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