Isuzu Rodeo UE. Manual — part 351

6E2–159

RODEO 6VD1 3.2L 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:

f

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.

f

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

°

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 P0125 –ECT Excessive Time to Closed Loop Fuel Control

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

Are any ECT sensor DTCs set?

—

Go to

applicable

ECT sensor

DTC chart

Go to

Step 3

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

4

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?

21

°

C (70

°

F)

Refer to

Diagnostic

Aids

Go to

Step 5

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

6E2–160

RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS

DTC P0125 –ECT Excessive Time to Closed Loop Fuel Control

(Cont'd)

Step

No

Yes

Value(s)

Action

6

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

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

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

9

Refer to

Cooling and Radiator for cooling system

diagnosis and repair condition as necessary.

Is the action complete?

—

Verify repair

—

10

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

Is the action complete?

—

Verify repair

—

11

Replace the ECT sensor.

Is the action complete?

—

Verify repair

—

12

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

—

6E2–161

RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) P0131 HO2S Circuit Low Voltage Bank 1

Sensor 1

D06RW081

Circuit Description

The powertrain control module (PCM) supplies a bias
voltage of about 450 mV between the heated oxygen
sensor (HO2S) signal high and signal low circuits. When
measured with a 10 megaohm digital voltmeter, this may
display as low as 350 mV. The oxygen sensor varies the
voltage within a range of about 1000 mV when the
exhaust is rich, down through about 10 mV when exhaust
is lean. The PCM constantly monitors the HO2S signal
during “closed loop” operation and compensates for a rich
or lean condition by decreasing or increasing injector
pulse width as necessary. If the Bank 1 HO2S 1 voltage
remains excessively low for an extended period of time,
DTC P0131 will be set.

Conditions for Setting the DTC

f

No related DTCs.

f

Vehicle is operating in “closed loop.”

f

Engine coolant temperature is above 60

°

C (140

°

F)

f

“Closed loop” commanded air/fuel ratio is between
14.5 and 14.8.

f

Throttle angle is between 3% and 19%.

f

Bank 1 HO2S 1 signal voltage remains below 22 mV
during normal “closed loop” operation for a total of 77
seconds over a 90-second period of time.

Action Taken When the DTC Sets

f

The PCM will illuminate the malfunction indicator lamp
(MIL) the first time the fault is detected.

f

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

f

“Open loop” fuel control will be in effect.

Conditions for Clearing the MIL/DTC

f

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.

f

A history DTC P0131 will clear after 40 consecutive
warm-up cycles have occurred without a fault.

f

DTC P0131 can be cleared by using the Tech 2 “Clear
Info” function or by disconnecting the PCM battery
feed.

Diagnostic Aids

Check for the following conditions:

f

Heated oxygen sensor wiring – The sensor pigtail may
be routed incorrectly and contacting the exhaust
system.

f

Poor PCM to engine block grounds.

f

Fuel pressure – The system will go lean if pressure is
too low. The PCM can compensate for some

6E2–162

RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS

decrease. However, If fuel pressure is too low, a DTC
P0131 may be set. Refer to

Fuel System Diagnosis.

f

Lean injector(s) – Perform “Injector Balance Test.”

f

Vacuum leaks – Check for disconnected or damaged
vacuum hoses and for vacuum leaks at the intake
manifold, throttle body, EGR system, and PCV system.

f

Exhaust leaks – An exhaust leak may cause outside air
to be pulled into the exhaust gas stream past the
HO2S, causing the system to appear lean. Check for
exhaust leaks that may cause a false lean condition to
be indicated.

f

MAF sensor – The system can go lean if the MAF
sensor signal indicates an engine airflow
measurement that is not correct. Disconnect the MAF
sensor to see if the lean condition is corrected. If so,
replace the MAF sensor.

f

Fuel contamination – Water, even in small amounts,
can be delivered to the fuel injectors. The water can
cause a lean exhaust to be indicated. Excessive

alcohol in the fuel can also cause this condition. Refer
to

Fuel System Diagnosis for the procedure to check

for fuel contamination.

f

If none of the above conditions are present, replace the
affected HO2S.

Test Description

Number(s) below refer to step numbers on the diagnostic
chart.
3. DTC P0131 failing during operation may indicate a

condition described in the “Diagnostic Aids” above.
If the DTC P0131 test passes while the Failure
Records conditions are being duplicated, an
intermittent condition is indicated.

Reviewing the Failure Records vehicle mileage since the
diagnostic test last failed may help determine how often
the condition that caused the DTC to be set occurs. This
may assist in diagnosing the condition.

DTC P0131 –HO2S Circuit Low Voltage Bank 1 Sensor 1

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. Install the Tech 2.
2. Run the engine at operating temperature.
3. Operate the vehicle within the parameters specified

under “Conditions for Setting the DTC” criteria
included in Diagnostic Support.

4. Using a Tech 2, monitor Bank 1 HO2S 1 voltage.

Does the Bank 1 HO2S 1 voltage remain below the
specified value?

22 mV

Go to

Step 4

Go to

Step 3

3

1. Ignition “ON,” engine “OFF,” review and record Tech

2 Failure Records data and note parameters.

2. Operate the vehicle within Failure Records

conditions as noted.

3. Using a Tech 2, monitor “DTC” info for DTC P0131

until the DTC P0131 test runs.

Note test result.

Does Tech 2 indicate DTC P0131 failed this ignition?

—

Go to

Step 4

Refer to

Diagnostic

Aids

4

1. Turn the ignition “OFF.”
2. Disconnect the PCM.
3. Check the Bank 1 HO2S 1 high and low circuits for a

short to ground or a short to the heater ground
circuit.

Are the Bank 1 HO2S 1 signal circuits shorted to
ground?

—

Go to

Step 5

Go to

Step 6

5

Repair the Bank 1 HO2S 1 signal circuit.

Is the action complete?

—

Verify repair

—

6

1. Turn the ignition “OFF,” HO2S 1 and PCM

disconnected.

2. Check for continuity between the high and low

signal circuits.

Was there continuity between the high and low circuits?

—

Go to

Step 7

Go to

Step 8