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Isuzu engine C22NE / 22LE / 20LE. Manual - part 81

DRIVEABILITY AND EMISSIONS 6E1-153

0.75

0.5

GRN

0.5

L/R

Engine

Control

Module

(ECM)

F14

ECT

Sensor

Input

Sensor

Ground

Engine

Coolant

Temperature

(ECT)

Sensor

TPS

OUT

DIAGNOSTIC TROUBLE CODE (DTC) (Flash DTC = 14)

ENGINE COOLANT TEMPERATURE (ECT) SENSOR CIRCUIT HIGH INPUT

Circuit Description

The engine coolant temperature (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. If the ECM

detect a continuous open in the ECT sensor or circuit,

then a code 14 will set.

Conditions for Setting the DTC

• Engine running time is longer than 10secs.
• The ECT sensor signal indicates an engine coolant

temperature greater than 140°C (284°F).

Action Taken When the DTC Sets

• The ECM will illuminate the malfunction indicator

lamp (MIL) 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.

6E1-154 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

176

332

140

667

113

1188

1802

2796

4450

7280

−5

12300

−15

21450

−30

−22

52700

−40

100700

DTC (Flash DTC = 14)

ECT Sensor Circuit High Input

Step

Action

Value(s)

Yes

Was the "On-Board Diagnostic (OBD) System Check"

performed?

Go to Step 2

Go to OBD

System

Check

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?

−35°C

(

−31°F)

Go to Step 4

Go to Step 3

1. Ignition ON engine OFF.

2. Using a Scan Tool, monitor the info for Diagnostic

Trouble Code 14.

Does the Scan Tool indicate Diagnostic Trouble Code 14.

Refer to Test

Description

Refer to

Diagnostic

Aids

1. Disconnect the ECT sensor electrical connector.

2. Jumper the ECT signal circuit and the sensor ground

circuit together at the ECT sensor harness connector.

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

Scan Tool.

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

140°C

(284°F)

Go to Step 6

Go to Step 5

DRIVEABILITY AND EMISSIONS 6E1-155

DTC (Flash DTC = 14)

ECT Sensor Circuit High Input (Cont'd)

Step

Action

Value(s)

Yes

1. Jumper the ECT signal circuit at the ECT sensor

harness connector to chassis ground.

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

Scan Tool.

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

140°C

(284°F)

Go to Step 7

Go to Step 6

Check for poor connections at the ECT sensor and

replace terminals if necessary.

Did any terminals require replacement?

Verify repair

Go to Step 8

1. Ignition OFF.

2. Disconnect the ECM, and check the ECT sensor

ground circuit for an Short to ground.

3. If the ECT sensor ground circuit is Short to ground,

repair it as necessary.

Was the ECT sensor ground circuit Short to ground?

Verify repair

Go to Step 8

Check for a poor sensor ground or ECT 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 9

Replace the ECT sensor.

Is the action complete?

Verify repair

Replace the EPROM or ECM.

Is the action complete?

Note) Refer to 6E1-243.

Verify repair

6E1-156 DRIVEABILITY AND EMISSIONS

Content .. 79 80 81 82 ..