Isuzu engine C22NE / 22LE / 20LE. Manual - part 82

DRIVEABILITY AND EMISSIONS  6E1-157

0.75

G

0.75

L

0.5

R

0.5

GRN

0.5

L/R

Engine

Control

Module

(ECM)

A3

F14

B1

B8

ECT

Sensor

Input

Sensor

Ground

Engine

Coolant

Temperature

(ECT)

Sensor

B

A

TPS

HI

OUT

LO

DIAGNOSTIC TROUBLE CODE (DTC) (Flash DTC = 15)

ENGINE COOLANT TEMPERATURE (ECT) SENSOR CIRCUIT LOW INPUT

Circuit Description

The ECT sensor is a thermistor mounted in the engine

coolant stream. The engine control module (ECM)

applies a voltage (about 5 volts) through a pull-up

resistor to the ECT signal circuit. When the engine

coolant is cold, the sensor (thermistor) resistance is

high, therefore the ECM will measure a high signal

voltage. As the engine coolant warms, the sensor

resistance becomes lower, and the ECT signal voltage

measured at the ECM drops. With a fully warmed-up

engine, the ECT signal voltage should measure about

1.5 to 2.0 volts.

Conditions for Setting the DTC

• Engine running time is longer than 30 secs.
• The ECT sensor signal indicates an engine coolant

temperature less than -35°C (-31°F).

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 substitute the ECT reading with a

default engine coolant temperature value. The

default value is based on start-up intake air

temperature and running 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.

6E1-158  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, If the harness appears to be OK, observe

the ECT display on the Scan Tool while moving

connectors and wiring harnesses related to the ECT

sensor. A change in the ECT display will indicate

the location of the fault.

Test Description

Number(s) below refer to the step number(s) on the

Diagnostic Chart.

2.  Verifies that the fault is present.

3.  Refer to the  "Temperature vs. Resistance Value"

table. The table may be used to test the ECT

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 ECT sensor. If the ECT sensor

appears to be OK, the fault is intermittent; refer to

Diagnostic Aids.

Engine Coolant 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 = 15)

Engine Coolant Temperature (ECT) Sensor Circuit Low Input

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.  Observe the  "Eng Coolant Temp" displayed on the

Scan Tool.

Is the  "Eng Coolant Temp"  below the specified value?

140°C

(284°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 15.

Does the Scan Tool indicate Diagnostic Trouble Code 15?

-

Go to Step 4

Refer to

Diagnostic

Aids

4

1.  Disconnect the ECT sensor electrical connector.

2.  Observe the  "Eng Coolant Temp" displayed on the

Scan Tool.

Is the  "Eng Coolant Temp"  at the specified value?

−35°C

(

−31°F)

Go to Step 6

Go to Step 5

DRIVEABILITY AND EMISSIONS  6E1-159

DTC (Flash DTC = 15)

Engine Coolant Temperature (ECT) Sensor Circuit Low Input (Cont'd)

Step

Action

Value(s)

Yes

No

5

1. Ignition OFF.

2.  Disconnect the ECM and check the ECT circuit for a an

open or a short to battery in the sensor circuit.

3.  If the ECT circuit is short to battery or open, repair it as

necessary.

Was the ECT signal circuit shorted to ground?

-

Verify repair

Go to Step 7

6

Replace the ECT sensor.

Is the action complete?

-

Verify repair

-

7

Replace the EPROM or ECM.

Is the action complete?

Note) Refer to 6E1-243.

-

Verify repair

-

6E1-160  DRIVEABILITY AND EMISSIONS