Isuzu Amigo / Axiom / Trooper / Rodeo / VehiCross. Manual - part 1439

6E2–207

RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) P0155 

HO2S Heater Circuit Open Bank 2 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 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.

6E2–208

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
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 for 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 P0155 – HO2S Heater Circuit Open 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

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 value?

Above

650 mV or

below

250 mV

Refer to

Diagnostic

Aids

Go to 

Step 3

3

Inspect the fuse for the Bank 2 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 2 HO2S 1 electrical connector.
4. Using a test light connected to a known good ground

(do not use Bank 2 HO2S 1 heater ground or Bank 2
HO2S 1 low), probe the ignition feed circuit at the
Bank 2 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 Bank 2 HO2S 1 ignition
feed and Bank 2 HO2S 1 heater ground.

Does the test light illuminate?

—

Go to 

Step 6

Go to 

Step 8

6E2–209

RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS

DTC P0155 – HO2S Heater Circuit Open Bank 2 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 resistance between the

Bank 2 HO2S 1 ignition feed and the Bank 2 HO2S 1
heater ground at the Bank 2 HO2S 1 pigtail.

Is the HO2S resistance within the specified values?

3-6 ohms

Go to 

Step 9

Go to 

Step 10

7

Repair the open Bank 2 HO2S 1 ignition feed circuit to
Bank 2 HO2S 1.

Is the action complete?

—

Verify repair

—

8

Repair the open Bank 2 HO2S 1 heater ground circuit.

Is the action complete?

—

Verify repair

—

9

1. Check for a poor connection at the Bank 2 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 2 HO2S 1 signal or low circuit
terminal connection at the Bank 2 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 2 HO2S 1 signal circuit and the Bank 2 HO2S
1 low circuit.

3. If the Bank 2 HO2S 1 signal 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 2 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 2 HO2S 1 signal 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 Bank 2 HO2S 1.

Is the action complete?

—

Verify repair

—

15

Locate and repair short to ground in Bank 2 HO2S 1
ignition feed circuit and replace the faulty fuse.

Is the action complete?

—

Verify repair

—

6E2–210

RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) 

P0157 HO2S Circuit Low Voltage Bank 2 Sensor 2

060R200054

Circuit Description

To control emissions of hydrocarbons (HC), carbon
monoxide (CO), and oxides of nitrogen (NOx), a
three-way catalytic converter is used.  The catalyst within
the converter promotes a chemical reaction which
oxidizes the HC and CO present in the exhaust gas,
converting them into harmless water vapor and carbon
dioxide.  The catalyst also reduces NOx, converting it to
nitrogen.  The powertrain control module (PCM) has the
ability to monitor this process using the Bank 2 HO2S 1
and the Bank 2 HO2S 2 heated oxygen sensors.  The
Bank 2 HO2S 1 sensor produces an output signal which
indicates the amount of oxygen present in the exhaust
gas entering the three-way catalytic converter.  The Bank
2 HO2S 2 sensor produces an output signal which
indicates the oxygen storage capacity of the catalyst; this
in turn indicates the catalyst’s ability to convert exhaust
gases efficiently.  If the catalyst is operating efficiently, the
Bank 2 HO2S 1 signal will be far more active than that
produced by the Bank 2 HO2S 2 sensor.  If the Bank 2
HO2S 2 signal voltage remains excessively low for an
extended period of time, DTC P0157 will be set.

Conditions for Setting the DTC

D

No related DTCs.

D

The 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

Bank 2 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 2 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 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 P0157 will clear after 40 consecutive
warm-up cycles have occurred without a fault.

D

DTC P0157 can be cleared by using the Tech 2 “Clear
Info” function or by disconnecting the PCM battery
feed.