Isuzu C22NE Workshop Manual page 358

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,
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,
Step
Was the "On-Board Diagnostic (OBD) System Check"
1 performed?
1. Ignition ON, engine OFF
2. Using a Scan Tool, monitor the intake air temperature
2 (IAT).
Is the intake air temperature greater then the specified
value?
1. Ignition ON, engine OFF Review and record Scan Tool
Failure Records data.
3 2. Using a Scan Tool, monitor the info for Diagnostic
Trouble Code 71.
Does the Scan Tool indicate Diagnostic Trouble Code 71?
improperly formed
DTC (Flash DTC = 71)
Intake Air Temperature (IAT) Sensor Too Low
Action
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,
or
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
Temperature vs. Resistance Values
100
80
60
45
35
25
15
5
−5
−15
−30
−40
Value(s)
-
140°C
(284°F)
-
°F OHMS
(approximate)
212
176
140
113
95
77
59
41
23 12300
5 21450
−22
52700
−40
100700
Yes
Go to OBD
System
Go to Step 2
Go to Step 4 Go to Step 3
Refer to
Refer to Test Diagnostic
Description
177
332
667
1188
1802
2796
4450
7280
No
Check
Aids