Isuzu Amigo / Axiom / Trooper / Rodeo / VehiCross. Manual - part 283

6E–162

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Aids

DTC P0125 set indicates a faulty ECT sensor.
Comparing the engine coolant temperature displayed on
a Tech 2 with actual coolant temperature measured with a
thermometer may isolate this condition. If the displayed
engine coolant temperature is not close to the actual
coolant temperature, replace the ECT sensor.
Check for the following conditions:

Poor connection at PCM – 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
display on the Tech 2 while moving connectors and
wiring harnesses related to the sensor. A change in the
display will indicate the location of the fault.

If DTC P0125 cannot be duplicated, the information
included in the Failure Records data can be useful in
determining vehicle mileage wince the DTC was last set.

Test Description

Number(s) below refer to the step number(s) on the
Diagnostic Chart.
2. Comparing the engine coolant temperature displayed

on a Tech 2 with actual coolant temperature
measured with a thermometer may isolate this
condition. If the displayed engine coolant
temperature is not close to the actual coolant
temperature, replace the ECT sensor. If the
temperatures are close, the fault is intermittent;
refer to

Diagnostic Aids.

Engine Coolant Temperature

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 P0125 –ECT Excessive Time to Closed Loop Fuel Control

Step

Action

Value(s)

Yes

Was the “On-Board Diagnostic (OBD) System Check”
performed?

—

Go to

Step 2

Go to

OBD

System

Check

Are any ECT sensor DTCs set?

—

Go to

applicable

ECT sensor

DTC chart

Go to

Step 3

1. Allow the engine to cool completely.
2. Check the cooling system coolant level (refer to

Cooling and Radiator).

Is the coolant level OK?

—

Go to

Step 4

Go to

Step 9

1. Start the engine.
2. With the engine idling, monitor “ENG COOL TEMP”

display on the Tech 2.

Does “ENG COOL TEMP” increase to above the
specified value within 2 minutes?

C (70

Refer to

Diagnostic

Aids

Go to

Step 5

Check for proper operation of the thermostat (refer to
Cooling and Radiator).

Is the thermostat operating correctly?

—

Go to

Step 6

Go to

Step 9

6E–163

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

DTC P0125 –ECT Excessive Time to Closed Loop Fuel Control

(Cont'd)

Step

Yes

Value(s)

Action

Compare engine coolant temperature displayed on the
Tech 2 to the actual coolant temperature measured
with a thermometer. (Observe normal precautions
when opening the cooling system.)

Is the Tech 2 engine coolant temperature indication
close to the measured temperature?

—

Go to

Step 9

Go to

Step 7

1. Ignition “OFF”.
2. Disconnect the PCM.
3. Using a DVM, measure the resistance of the ECT at

the PCM connector.

4. Compare the DVM reading with the chart in “Test

Description”.

Is the chart value approximately equal to the
thermometer reading?

—

Go to

Step 12

Go to

Step 8

Check for high resistance in wiring related to the ECT
sensor. Also, check for poor connections at the ECT
sensor and the PCM.

Was a problem found?

—

Go to

Step 10

Go to

Step 11

Refer to

Cooling and Radiator for cooling system

diagnosis and repair condition as necessary.

Is the action complete?

—

Verify repair

—

Replace the faulty terminal(s) or repair faulty wiring as
necessary.

Is the action complete?

—

Verify repair

—

Replace the ECT sensor.

Is the action complete?

—

Verify repair

—

Replace the PCM.

IMPORTANT: The replacement PCM must be
programmed. Refer to

On-Vehicle Service in

Powertrain Control Module and Sensors for
procedures.

And also refer to latest Service Bulletin.

Check to see if the Latest software is released or not.
And then Down Load the LATEST PROGRAMMED
SOFTWARE to the replacement PCM.

Is the action complete?

—

Verify repair

—

6E–164

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code(DTC)

P0128 Thermostat Insufficient Temperature for Stable Operation

060R200053

Circuit Description

The engine coolant temperature (ECT) sensor
thermistor mounted on a coolant crossover pipe at the
front of the engine.
This code determines if system has insufficient
coolant temperatures for stable operation.

Conditions for setting the DTC

Engine running.

No IAT, ECT and MAF DTCs set.

No VSS DTC set.

Warm case(Ambient temperature is between 50

F and

128

F.):

Time for coolant to reach stabilized closed loop value
is less than 239 sec.

Cold case(Ambient temperature is between 20

F and

F.):

Time for coolant to reach stabilized thermostat
regulation temperature is more than 263 sec.

Action Taken When the DTC Sets

The PCM will ON the MIL after second trip with
detected fault.

The PCM will store conditions which were present
when the DTC was set as Freeze Frame and in the
Failure Records data.

Conditions for Clearing the MIL/DTC

The PCM will turn the MIL “OFF” on the third
consecutive trip cycle during which the diagnostic has
been run and the fault condition is no longer present.

A history DTC P0128 will clear after 40 consecutive trip
cycles during which the warm up cycles have occurred
without a fault.

DTC P0128 can be cleared using the Tech 2 “Clear
Info” function or by disconnecting the PCM battery
feed.
Tech 2 “Clear Info” function or by disconnecting the
PCM battery feed.

Diagnostic Aids

An intermittent may be caused by the following:

Poor connections.

Misrouted harness.

Rubbed through wire insulation.

Broken wire inside the insulation.

Check for the following conditions:

Poor connection at PCM–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.

6E–165

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

If the harness appears to be OK, observe the ECT
display on the Tech2 while moving connectors and
wiring harnesses related to the sensor.

A change in the display will indicate the location of
the fault.

If DTC P0128 cannot be duplicated, the information
included in the Failure Records data can be useful in

determined vehicle mileage since the DTC was last
set.

If it is determined that the DTC occurs intermittently,
performing the DTC P0128 Diagnostic Chart may
isolate the cause of the fault.

Diagnostic Trouble Code (DTC)

P0128 Thermostat Insufficient Temperature for stable operation

Step

Action

Value(s)

Yes

Was the “On-Board(OBD)System Check” performed?

—

Go to

Step 2

Go to

OBD

System

Check

1. Visually/physically check air duct and water pipe for

splits, kinks, and proper connections and routing.

2. If a problem is found, repair as necessary.

Was a problem found?

—

Verify repair

Go to

Step 3

1. Remove and check the Thermostat for stable

operation. Refer to

6B section.

2. Replace the thermostat if necessary.

Was a problem found?

—

Verify repair

Go to

Step 4

1. Ignition “ON”, engine “OFF”.
2. Review and record Tech 2 Failure Records.
3. Operate the vehicle within Failure Records

conditions as noted.

4. Using a Tech 2, monitor “DTC” info for DTC P0128.

Does the Tech 2 indicate DTC P0128 failed this
ignition?

—

Go to

Step 5

Refer to

Diagnostic

Aids

1. Ignition “ON”, engine “OFF”.
2. Oberve the “Eng Cool Temp” display on the Tech 2.

Is the “Eng Cool Temp” below the specified value?

139

(282

Verify repair

Go to

Step 6

1. Ignition “OFF”.
2. Disconnect the PCM and check the ECT signal

circuit for a short to ground or a short to the sensor
ground circuit.

3. If the ECT signal circuit is shorted, repair it as

necessary.

Was a problem found?

—

Verify repair

Refer to

Diag-

nostic

Go to

Step 7

Replace the PCM.

IMPORTANT:
The replacement PCM must be programmed.
Refer to

ON-Vehicle Service in Power Control Module

and Sensors for procedures.
And also refer to latest Service Bulletin.
Check to see if the latest software is released or not.
And then Down Load the LATEST PROGRAMMED
SOFTWARE to the replacement PCM.

Is the action complete?

—

Verify repair

—

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