Isuzu Amigo / Axiom / Trooper / Rodeo / VehiCross. Manual - part 1432

6E2–179

RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) 

P0135 HO2S Heater Circuit Bank 1 Sensor 1

060R200054

Circuit Description

Heated oxygen sensors are used to minimize the amount
of time required for “closed loop” fuel control operation
and to allow accurate catalyst monitoring.  The oxygen
sensor heater greatly decreases the amount of time
required for fuel control sensors Bank 1 HO2S 1 and Bank
2 HO2S 1 to become active.  Oxygen sensor heaters are
required by post-catalyst monitor sensors  to maintain a
sufficiently high temperature which allows accurate
exhaust oxygen content readings further from the engine.
The powertrain control module (PCM) will run the heater
test only after a cold start (determined by engine coolant
and intake air temperature at the time of start-up) and only
once during an ignition cycle.  When the engine is started
the PCM will monitor the HO2S voltage.  When the HO2S
voltage indicates a sufficiently active sensor, the PCM
looks at how much time has elapsed since start-up.  If the
PCM determines that too much time was required for the
Bank 1 HO2S 1 to become active, a DTC P0135 will set.
The time it should take the HO2S to reach operating
temperature is based on the accumulated amount of air
that has passed through the MAF sensor and into the
engine (more accumulated air flow = shorter time to
HO2S activity).

Conditions for Setting the DTC

D

The engine has been running for over 120 seconds.

D

Heater signal is below 0.1A.

D

Bank 1 HO2S 1 voltage does not change more than
150 mV from the bias voltage (between 400 mV and
500 mV) for a longer amount of time than it should.  The
maximum amount of time to come up to operating
range is 150 seconds.  This warm-up time depends on
the engine coolant temperature at start-up and
accumulate air flow since start-up.

Action Taken When the DTC Sets

D

The PCM will illuminate the malfunction indicator lamp
(MIL) after the second consecutive trip in which the
fault is detected.

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 P0135 will clear after 40 consecutive
warm-up cycles have occurred without a fault.

D

DTC P0135 can be cleared by using the Tech 2 “Clear
Info” function or by disconnecting the PCM battery
feed.

6E2–180

RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Aids

Check for the following conditions:

D

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.

D

Damaged harness – Inspect the wiring harness for
damage.  If the harness appears to be OK, observe the
ECT 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.

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.

Test Description

Number(s) below refer to the step number(s) on the
Diagnostic Chart.

2. The HO2S should be allowed to cool before

performing this test.  If the HO2S heater is
functioning, the signal voltage will gradually increase
or decrease as the sensor element warms.  If the
heater is not functioning, the HO2S signal will
remain near the 450 mV bias voltage.

4. Ensures that the ignition feed circuit to the HO2S is

not open or shorted.  The test light should be
connected to a good chassis ground, in case the
HO2S low or HO2S heater ground circuit is faulty.

5. Checks the HO2S heater ground circuit.

6. Checks or an open or shorted HO2S heater element.

10.An open HO2S signal or low circuit can cause the

HO2S heater to appear faulty.  Check these circuits
before replacing the sensor.

DTC P0135 – HO2S Heater Circuit 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

NOTE: If the engine has just been operating ,allow the
engine to cool for at least 15 minutes before
proceeding.

1. Remove the fuel pump relay.
2. Connect a fused jumper at the fuel pump relay

socket, between the battery positive at the relay and
the relay wire that leads to the fuel pump and HO2S
fuses.

3. Ignition “OFF”.
4. Install a Tech 2.
5. Ignition “ON”, engine “OFF”.
6. Monitor the Bank 1 HO2S 1 voltage for several

minutes.

Did the HO2S voltage go from bias voltage to above or
below the specified values?

Above

650 mV or

below

250 mV

Refer to

Diagnostic

Aids

Go to 

Step 3

3

Inspect the fuse for the Bank 1 HO2S 1 ignition feed.

Is the fuse open?

—

Go to 

Step 15

Go to 

Step 4

4

1. Ignition “OFF”.
2. Raise the vehicle.
3. Disconnect the Bank 1 HO2S 1 electrical connector.
4. Using a test light connected to a good ground (do

not use Bank 1 HO2S 1 heater ground or Bank 1
HO2S 1 low), probe the ignition feed circuit at the
Bank 1 HO2S 1 electrical connector (PCM harness
side).

Does the test light illuminate?

—

Go to 

Step 5

Go to 

Step 7

5

Connect the test light between the Bank 1 HO2S 1
ignition feed and the Bank 1 HO2S 1 heater ground.

Does the test light illuminate?

—

Go to 

Step 6

Go to 

Step 8

6E2–181

RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS

DTC P0135 – HO2S Heater Circuit Bank 1 Sensor 1

  (Cont'd)

Step

No

Yes

Value(s)

Action

6

1. Allow the HO2S to cool for at least 15 minutes.
2. Using a DVM, measure the resistance between the

Bank 1 HO2S 1 ignition feed and the Bank 1 HO2S 1
heater ground at the Bank 1 HO2S 1 pigtail.

Is the HO2S heater resistance within the specified
values?

3-6 ohms

Go to 

Step 9

Go to 

Step 10

7

Repair the open Bank 1 HO2S 1 ignition feed circuit to
Bank 1 HO2S 1.

Is the action complete?

—

Verify repair

—

8

Repair the open Bank 1 HO2S 1 heater ground circuit
to Bank 1 HO2S 1.

Is the action complete?

—

Verify repair

—

9

1. Check for a poor connection at the Bank 1 HO2S 1

harness terminals.

2. If a poor connection is found, replace terminals.

Was a poor connection found?

—

Verify repair

Go to 

Step 10

10

Check for a poor Bank 1 HO2S 1 high or low circuit
terminal connection at the Bank 1 HO2S 1 harness
connector and replace terminal(s) if necessary.

Did any terminals require replacement?

—

Verify repair

Go to 

Step 11

11

1. Ignition “OFF”.
2. Disconnect the PCM and check the continuity of the

Bank 1 HO2S 1 signal circuit and the Bank 1 HO2S
1 low circuit.

3. If the Bank 1 HO2S 1 high circuit or HO2S low circuit

measures over 5 ohms, repair open or poor
connection as necessary.

Was a problem found?

—

Verify repair

Go to 

Step 12

12

Check for a poor Bank 1 HO2S 1 low circuit terminal
connection at the PCM and replace the terminal if
necessary.

Did the terminal require replacement?

—

Verify repair

Go to 

Step 13

13

Check for a poor Bank 1 HO2S 1 high circuit terminal
connection at the PCM and replace the terminal if
necessary.

Did the terminal require replacement?

—

Verify repair

Go to 

Step 14

14

Replace the Bank 1 HO2S 1.

Is the action complete?

—

Verify repair

—

15

Locate and repair the short to ground in Bank 1 HO2S 1
ignition feed circuit and replace the fault fuse.

Is the action complete?

—

Verify repair

—

6E2–182

RODEO 6VD1 3.2L 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