Isuzu Trooper (1998-2002 year). Manual - part 460

6E–210

6VE1 3.5 ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Aids

Check for the following conditions:

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.

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. This 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. This checks the HO2S heater ground circuit.

6. This checks for an open or shorted HO2S heater

element.

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

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

DTC P0161 – HO2S Heater Circuit Bank 2 Sensor 2

Step

Action

Value(s)

Yes

Was the “On-Board Diagnostic (OBD) System Check”
performed?

—

Go to

Step 2

Go to

OBD

System

Check

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 2 HO2S 2 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

Check the

Procedure

Refer to

Diagnostic

Aids

Go to

Step 3

Inspect the fuse for the Bank 2 HO2S 2 ignition feed.

Is the fuse open?

—

Go to

Step 15

Go to

Step 4

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

(do not use Bank 2 HO2S 2 heater ground or Bank 2
HO2S 2 low), probe the ignition feed circuit at the
Bank 2 HO2S 2 electrical connector (PCM harness
side).

Does the test light illuminate?

—

Go to

Step 5

Go to

Step 7

Connect the test light between the Bank 2 HO2S 2
ignition feed and the Bank 2 HO2S 2 heater ground.

Does the test light illuminate?

—

Go to

Step 6

Go to

Step 8

6E–211

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

DTC P0161 – HO2S Heater Circuit Bank 2 Sensor 2

(Cont'd)

Step

Yes

Value(s)

Action

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

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

Is the HO2S resistance within the specified values?

3-6 ohms

Go to

Step 9

Go to

Step 10

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

Is the action complete?

—

Verify repair

—

Repair the open Bank 2 HO2S 2 heater ground circuit.

Is the action complete?

—

Verify repair

—

1. Check for a poor connection at the Bank 2 HO2S 2

harness terminals.

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

Was a poor connection found?

—

Verify repair

Go to

Step 10

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

Bank 2 HO2S 2 signal circuit and the Bank 2 HO2S
2 low circuit.

3. If the Bank 2 HO2S 2 signal circuit or HO2S low

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

Was a problem found?

—

Verify repair

Go to

Step 11

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

Bank 2 HO2S 2 signal circuit and the Bank 2 HO2S
2 low circuit.

3. If the Bank 2 HO2S 2 signal circuit or HO2S low

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

Was a problem found?

—

Verify repair

Go to

Step 12

Check for a poor Bank 2 HO2S 2 low circuit terminal
connection at the PCM and replace the terminal if
necessary.

Did the terminal require replacement?

—

Verify repair

Go to

Step 13

Check for a poor Bank 2 HO2S 2 high circuit terminal
connection at the PCM and replace the terminal if
necessary.

Did the terminal require replacement?

—

Verify repair

Go to

Step 14

Replace Bank 2 HO2S 2.

Is the action complete?

—

Verify repair

—

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

Is the action complete?

—

Verify repair

—

6E–212

6VE1 3.5 ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC)

P0171 Fuel Trim System Lean Bank 1

D06R200010

Circuit Description

To provide the best possible combination of driveability,
fuel economy, and emission control, a “closed loop”
air/fuel metering system is used. While in “closed loop”,
the powertrain control module (PCM) monitors the Bank 1
HO2S 1 and Bank 2 HO2S 1 signals and adjusts fuel
delivery based upon the HO2S signal voltages. A change
made to fuel delivery will be indicated by the long and
short term fuel trim values which can be monitored with a
Tech 2. Ideal fuel trim values are around 0%; if the HO2S
signals are indicating a lean condition the PCM will add
fuel, resulting in fuel trim values above 0%. If a rich
condition is detected, the fuel trim values will be below
0%, indicating that the PCM is reducing the amount of fuel
delivered. If an excessively lean condition is detected on
Bank 1, the PCM will set DTC P0171.
The PCM’s maximum authority to control long term fuel
trim allows a range between –15% (automatic
transmission) or –12% (manual transmission) and +20%.
The PCM monitors fuel trim under various engine
speed/load fuel trim cells before determining the status of
the fuel trim diagnostic.

Conditions for Setting the DTC

None of the following: EGR DTCs, HO2S DTCs,
(response, transition, open, low volts, no activity), MAF
DTCs, TP sensor DTCs, MAP DTCs, IAT DTCs,
canister purge DTCs, EVAP DTCs, injector circuit
DTCs, or misfire DTCs.

Engine coolant temperature is between 6

C (42.8

and 105

C (221

F).

Intake air temperature is between –40

C (–40

F) and

120

C (248

F).

Manifold absolute pressure is between 24 kPa and 99
kPa.

Throttle angle is steady below 95%.

Vehicle speed is below 136 km/h (85 mph).

Engine speed is between 400 and 6,000 RPM.

Barometric pressure is greater than 72.5 kPa.

Mass air flow is between 2 g/second and 200 g/second.

Ignition voltage is above 9.5 volts.

Fuel system is in “closed loop”.

Canister purge duty cycle is greater than 0% if on.

Action Taken When the DTC Sets

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

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

6E–213

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

Conditions for Clearing the MIL/DTC

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.

A history DTC P0171 will clear after 40 consecutive
warm-up cycles have occurred without a fault.

DTC P0171 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:

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.

Damaged harness – Inspect the wiring harness for
damage. If the harness appears to be OK, observe the
Bank 1 HO2S 1 display on the Tech 2 while moving
connectors and wiring harnesses related to the engine
harness. A change in the display will indicate the
location of the fault.

Test Description

Number(s) below refer to the step number(s) on the
Diagnostic Chart.
2. DTCs other than P0171 and P0174 may indicate a

condition present which may cause a lean condition.
If this is the case, repairing the condition which
caused the other DTC will most likely correct the
DTC P0171/P0174.

4. If the DTC P0171 test passes while the Failure

Records conditions are being duplicated, the lean
condition is intermittent. Refer to

Diagnostic Aids or

Symptoms for additional information on diagnosing
intermittent problems.

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