Isuzu Amigo / Axiom / Trooper / Rodeo / VehiCross. Manual - part 288

6E–182

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) 

P0137 HO2S Circuit Low Voltage Bank 1 Sensor 2

060R200054

Circuit Description

The powertrain control module (PCM) supplies bias
voltage of about 450 mV between the heated oxygen
sensor (HO2S) signal high and signal low circuits.  When
measured with a 10 megaohm impedance digital
voltmeter, this may display as low as 350 mV.  The
oxygen sensor varies the voltage within a range of about
1000 mV when exhaust is rich, down through about
10 mV when the 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 2 signal voltage remains
excessively low for an extended period of time, DTC
P0137 will be set.

Conditions for Setting the DTC

D

No related DTCs.

D

Engine is operating in “closed loop”.

D

Engine coolant temperature is above 60

°

C (140

°

F).

D

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

D

Throttle angle is between 3% and 19%.

D

Bank 1 HO2S 2 signal voltage remains below 22 mV
during normal “closed loop” operation for a total of 106
seconds over a 125-second period of time.

OR

D

Bank 1 HO2S 2 signal voltage remains below 400 mV
during power enrichment mode fuel control operation
for up to 5 seconds.

Action Taken When the DTC Sets

D

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

D

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

Conditions for Clearing the MIL/DTC

D

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.

D

A history DTC P0137 will clear after 40 consecutive
warm-up cycles have occurred without a fault.

D

DTC P0137 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:

D

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

D

Poor PCM to engine grounds.

D

Fuel pressure – A condition which causes a lean
exhaust can cause DTC P0137 to set.  The system will
go lean if pressure is too low.  The PCM can

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6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

compensate for some decrease.  However, if fuel
pressure is too low, a DTC P0137 may be set.  Refer
to 

Fuel System Diagnosis.

D

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

D

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

D

Exhaust leaks – An exhaust leak may cause outside air
to be pulled into the exhaust gas stream past the
HO2S, causing the DTC P0137 to set.  Check for
exhaust leaks near the Bank 1 HO2S 2 sensor.

D

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.

D

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 procedure to check for

fuel contamination.

D

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

Test Description

Number(s) below refer to the step number(s) on the
Diagnostic Chart.
3. DTC P0137 failing during operation may indicate a

condition described in the “Diagnostic Aids” above.
If the DTC0137 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 P0137 –HO2S Circuit Low Voltage Bank 1 Sensor 2

 

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 2 voltage.

Does the Bank 1 HO2S 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 P0137

until the DTC P0137 test runs.

4. Note the test result.

Does the Tech 2 indicate DTC P0137 failed this
ignition?

—

Go to 

Step 4

Refer to

Diagnostic

Aids

4

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

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

Were Bank 1 HO2S 2 signal circuits shorted?

—

Go to 

Step 5

Go to 

Step 6

5

Repair the Bank 1 HO2S 2 signal circuit.

Is the action complete?

—

Verify repair

—

6

1. Ignition “OFF”.
2. Leave the PCM and HO2S 2 disconnected.
3. 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

6E–184

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

DTC P0137 –HO2S Circuit Low Voltage Bank 1 Sensor 2

  (Cont'd)

Step

No

Yes

Value(s)

Action

7

Repair the short between the high and low circuits.

Is the action complete?

—

Verify repair

—

8

1. Ignition “OFF”.
2. Reconnect the PCM, leave HO2S 2 disconnected.
3. Ignition “ON”.

Does the Tech 2 indicate Bank 1 HO2S 2 voltage near
the specified value?

425-475 mV

Refer to

Diagnostic

Aids

Go to 

Step 9

9

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–185

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) 

P0138 HO2S Circuit High Voltage Bank 1 Sensor 2

060R200054

Circuit Description

The powertrain control module (PCM) supplies 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 320 mV.  The oxygen sensor varies the
voltage within a range of about 1000 mV when exhaust is
rich, down through about 10 mV when the 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 2 voltage
remains excessively high for an extended period of time,
DTC P0138 will be set.

Conditions for Setting the DTC

D

No related DTCs.

D

Engine is operating in “closed loop”.

D

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

D

Engine coolant temperature is above 60

°

C (140

°

F).

D

Throttle angle is between 3% and 19%.

D

Bank 1 HO2S 2 signal voltage remains above 952 mV
during normal “closed loop” operation for a total of 106
seconds over a 125-second period of time.

OR

D

Bank 1 HO2S 2 signal voltage remains above 500 mV
during deceleration fuel cut–off mode operation for up
to 3 seconds.

Action Taken When the DTC Sets

D

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

D

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

D

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.

D

A history DTC P0138 will clear after 40 consecutive
warm-up cycles have occurred without a fault.

D

DTC P0138 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:

D

Fuel pressure – An excessively rich fuel mixture can
cause a DTC P0138 to be set.  Refer to 

Fuel System

Diagnosis.

D

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

D

Leaking injector – Refer to 

Fuel System Diagnosis.