Isuzu Trooper (1998-2002 year). Manual - part 456

6E–194

6VE1 3.5 ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) 

P0154 HO2S Circuit Insufficient Activity Bank 2 Sensor 1

D06RY00175

Circuit Description

The powertrain control module (PCM) supplies a bias
voltage of about 450 mV between the heated oxygen
sensor (HO2S) high and 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 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 2 HO2S 1 voltage remains at or
near the 450 mV bias for an extended period of time, DTC
P0154 will be set, indicating an open sensor signal or
sensor low circuit.
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 for accurate exhaust oxygen
content readings further from the engine.

Conditions for Setting the DTC

D

No related DTCs.

D

Engine coolant temperature is above 60

°

C (140

°

F).

D

The engine has been running for over 5 seconds.

D

Oxygen sensor heater is functioning properly.

D

Bank 2 HO2S 1 signal voltage remains between
400 mV and 500 mV for a total of 77 seconds over a
90-second period of time.

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.

D

“Open loop” fuel control will be in effect.

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 P0154 will clear after 40 consecutive
warm-up cycles have occurred without a fault.

D

DTC P0154 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

Poor connection or damaged harness – Inspect the
harness connectors for backed-out terminals,

6E–195

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

improper mating, broken locks, improperly formed or
damaged terminals, poor terminal-to-wire-connection,
and damaged harness.

D

Faulty HO2S heater or heater circuit – With the ignition
“ON”, engine “OFF”, the HO2S 1 voltage displayed on
the Tech 2 is normally 455-460 mV.  A reading over
1000 mV indicates a signal line shorted to voltage.  A
reading under 5 mV indicates a signal line shorted to
ground or signal lines shorted together.  If not,
disconnect the HO2S and connect a test light between
the HO2S ignition feed and heater ground circuits.  If
the test light does not light for 2 seconds when the
ignition is turned on, repair the open ignition feed or
sensor ground circuit as necessary.  If the test light
lights and the HO2S signal and low circuits are OK,
replace the HO2S.

D

Intermittent test – With the ignition “ON”, monitor the
HO2S signal voltage while moving the wiring harness

and related connectors.  If the fault is induced, the
HO2S signal voltage will change.  This may help isolate
the location of the malfunction.

Test Description

Number(s) below refer to the step number(s) on the
Diagnostic Chart.
3. If the DTC P0154 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 P0154 –HO2S Circuit Insufficient Activity Bank 2 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 engine above 1200 RPM for two

minutes.

Does the Tech 2 indicate Bank 2 HO2S 1 voltage
varying outside the specified values?

400-500 mV

Go to 

Step 3

Go to 

Step 4

3

1. Ignition “ON”, engine “OFF”.
2. Review and record Tech 2 Failure Records data and

note parameters.

3. Operate the vehicle within Failure Records

conditions as noted.

4. Using a Tech 2, monitor “DTC” info for DTC P0154

until the DTC P0154 test runs.

5. Note the test result.

Does the Tech 2 indicate DTC P0154 failed this
ignition?

—

Go to 

Step 4

Check the

Procedure

Refer to

Diagnostic

Aids

4

Check for a damaged harness.

Was a problem found?

—

Verify repair

Go to 

Step 5

5

Check for a poor Bank 2 HO2S 1 high and low circuit
terminal connections at the Bank 2 HO2S 1 harness
connector and replace terminal(s) if necessary.

Did any terminals require replacement?

—

Verify repair

Go to 

Step 6

6

Check for a poor Bank 2 HO2S 1 high and low circuit
terminal connections at the PCM and replace
terminal(s) if necessary.

Did the terminal require replacement?

—

Verify repair

Go to 

Step 7

6E–196

6VE1 3.5 ENGINE DRIVEABILITY AND EMISSIONS

DTC P0154 –HO2S Circuit Insufficient Activity Bank 2 Sensor 1

  (Cont'd)

Step

No

Yes

Value(s)

Action

7

1. Ignition “OFF”.
2. With the PCM disconnected, check continuity of the

Bank 2 HO2S 1 high circuit.

3. If the Bank 2 HO2S 1 high circuit measures over 5.0

ohms, repair open or poor connection as necessary.

Was a Bank 2 HO2S 1 high circuit problem found and
corrected?

—

Verify repair

Go to 

Step 8

8

1. Ignition “OFF”.
2. With the PCM disconnected, check continuity of the

Bank 2 HO2S 1 low circuit.

3. If the Bank 2 HO2S 1 low circuit measures over 5.0

ohms, repair open or poor connection as necessary.

Was a Bank 2 HO2S 1 low circuit problem found and
corrected?

—

Verify repair

Go to 

Step 9

9

1. Ignition “ON”, engine “OFF”.
2. Disconnect Bank 2 HO2S 1 and jumper the HO2S

high and low circuits (PCM side) to ground.

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

Is the Bank 2 HO2S 1 voltage in the specified range?

0-10 mV

Go to 

Step 10

Go to 

Step 11

10

Replace Bank 2 HO2S 1.

Is the action complete?

—

Verify repair

—

11

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–197

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) 

P0155 HO2S Heater Circuit Open Bank 2 Sensor 1

D06RY00175

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 Bank
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 2 HO2S 1 to become active, a DTC P0155
will set.  The time it should take the HO2S to reach
operating temperature is based on the total amount of air
that has passed through the mass air flow (MAF) sensor
and into the engine (more total air flow = shorter time to
HO2S activity).

Conditions for Setting the DTC

D

No related DTCs.

D

The engine has been running for over 120 seconds.

D

Ignition voltage is between 11 volts and 18 volts.

D

Heater signal is below 0.1A.

D

Bank 1 HO2S 2 voltage does not change more than
150 mV from the bias voltage (between
400 mV-500 mV) for a longer amount of time than it
should.  The maximum amount of time to come up to
operating range is 120 seconds.  This warm-up time
depends on the engine coolant temperature at start-up
and accumulated 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 P0155 will clear after 40 consecutive
warm-up cycles have occurred without a fault.

D

DTC P0155 can be cleared by using the Tech 2 “Clear
info” function or by disconnecting the PCM battery
feed.