Isuzu 4HL1 Workshop Manual page 107

Step
Check the harness between ECM and IAT
sensor for open wiring.
1. Starter switch "OFF".
2. Disconnect the ECM.
3. Disconnect the IAT sensor connector.
7
4. Jumper the IAT sensor connector pins
and measure the resistance at the ECM
connector.
Was the resistance within range?
Check the IAT sensor circuit for short.
1. Starter switch "OFF".
2. Disconnect the ECM.
8
3. At the ECM connector, measure the
resistance.
Was the resistance within range?
Check the harness between ECM and IAT
sensor for short.
1. Starter switch "OFF".
2. Disconnect the ECM.
9
3. Disconnect the IAT sensor connector.
4. At the ECM connector, measure the
resistance.
Was the resistance within range?
Repair or replace the faulty harness.
10
Is the action complete?
Check the IAT sensor.
1. Disconnect the IAT sensor.
2. Provide temperature change on the
thermosensitive element of the IAT
11
sensor and measure the resistance
between the sensor connector pins.
Was the resistance within range?
Replace the IAT sensor.
12
Is the action complete?
Review the DTC.
1. Certainly connect the IAT sensor and
ECM connectors.
13
2. Using Tech 2, clear the DTC.
3. Perform test run and review the DTC.
Is DTC22 detected?
1. Replace the ECM.
IMPORTANT:
If necessary (for the vehicle equipped with
14
idle stop function), input the number of
startups to the replacing ECM.
Is the action complete?
Action
Engine Control System 1A-105
Value(s)
Pins 91-83
(jumpered:
pins 1-2): 0 Ω
Pins 91-83-
ground
(jumpered:
pins 1/2-
ground): 0 Ω
Go to Step 11
Pins 91-83:
2.5 kΩ (ECT:
approx. 20°C)
Pins 91/83-
ground: ∞ Ω
Go to Step 13
Pins 91-83:
∞ Ω
Pins 91/83-
ground: ∞ Ω
Go to Step 11
Verify repair and
—
go to Step 15
See graph
Go to Step 13
Verify repair and
—
go to Step 15
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Go to Step 14
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Verify repair and
go to Step 15
Yes No
Go to Step 10
Go to Step 9
Go to Step 10
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Go to Step 12
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Refer to
Diagnostic Aids
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