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