Isuzu Trooper (1998-2002 year). Service manual — part 312
6E–161
ENGINE DRIVEABILITY AND EMISSIONS
DTC P0172 – Fuel Trim System Rich Bank 1
(Cont'd)
Step
No
Yes
Value(s)
Action
11
1. Disconnect the vacuum hose from the fuel pressure
regulator and inspect the hose for the presence of
fuel.
2. If fuel is present in the vacuum hose, replace the
fuel pressure regulator (refer to
Fuel Metering
System).
Did the fuel pressure regulator require replacement?
—
Verify repair
Go to
Step 12
12
Ignition “ON,” engine “OFF,” monitor the TP Angle
display on the Tech 2 while slowly depressing the
accelerator pedal.
Does the TP Angle display increase steadily and
evenly from minimum value at closed throttle to
maximum value at wide-open throttle?
Minimum 0%
Maximum
100%
Go to
Step 13
Go to
Step 18
13
1. Disconnect the MAF sensor electrical connector.
2. Operate the vehicle in “closed loop” while
monitoring the “BANK 1 L.T. FUEL TRIM” and
“BANK 1 S. T. FUEL TRIM” display on the Tech 2.
Did both values change to near the specified value?
0%
Go to
Step 19
Go to
Step 14
14
1. Perform “Fuel System Pressure Test.”
2. If Fuel System Pressure Test isolates a problem,
repair as necessary (refer to
Engine Fuel or Fuel
Metering System).
Did the Fuel System Pressure Test isolate a problem
requiring repair?
—
Verify repair
Go to
Step 16
15
Replace the PCM.
IMPORTANT: The replacement PCM must be
programmed. Refer to
UBS 98model year Immobilizer
Workshop Manual.
Is the action complete?
—
Verify repair
—
16
1. Perform the “Injector Balance Test.”
2. If Injector Balance Test isolates a problem, repair as
necessary (refer to
Fuel Metering System).
Did the Injector Balance Test isolate a problem
requiring repair?
—
Verify repair
Go to
Step 17
17
1. Remove and visually/physically inspect the Bank 1
HO2S 1 for silicon contamination. This will be
indicated by a powdery white deposit on the portion
of the HO2S that is exposed to the exhaust stream.
2. If contamination is evident on the Bank 1 HO2S 1,
replace the contaminated sensors.
Did the sensor require replacement?
—
Verify repair
Refer to
Diagnostic
Aids
18
1. Check the TP sensor mounting screws and tighten
or replace them as necessary if they are loose or
missing.
2. If the screws are OK, replace the TP sensor.
Is the action complete?
—
Verify repair
—
19
Replace the MAF sensor.
Is the action complete?
—
Verify repair
—
6E–162
ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0174 Fuel Trim System Lean Bank 2
D06RW031
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 2, the PCM will set DTC P0174.
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
D
No Tech 2 test is being run.
D
None of the following DTCs are set: idle system, EGR,
HO2S, (response, transition, open, low volts, no
activity), MAF, TP sensor, MAP, IAT, canister purge,
EVAP, injector circuit, or misfire.
D
Engine coolant temperature is between 25
°
C (77
°
F)
and 100
°
C (212
°
F).
D
Intake air temperature is between –40
°
C (–40
°
F) and
120
°
C (248
°
F).
D
Manifold absolute pressure is between 24 kPa and 99
kPa.
D
Throttle angle is steady below 95%.
D
Vehicle speed is below 136 km/h (85 mph).
D
Engine speed is between 400 and 6,000 RPM.
D
Barometric pressure is greater than 72.5 kPa.
D
Mass air flow is between 2 g/second and 200 g/second.
6E–163
ENGINE DRIVEABILITY AND EMISSIONS
D
Ignition voltage is above 9.5 volts.
D
Fuel system is in “closed loop.”
Action Taken When the DTC Sets
D
The PCM will illuminate the malfunction indicator lamp
(MIL) after the second consecutive trip in which the
failure 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
DTC P0174 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 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
Bank 2 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.
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. 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 P0174 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.
6E–164
ENGINE DRIVEABILITY AND EMISSIONS
DTC P0174 – Fuel Trim System Lean Bank 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
Are any DTCs set other than P0174 and P0171?
—
Go to the
applicable
DTC charts
and repair the
other DTCs
before
proceeding
with this
chart.
Go to
Step 3
3
1. Start the engine and operate the vehicle in “closed
loop.”
2. Observe the “BANK 2 L.T. FUEL TRIM” display on
the Tech 2.
Is the displayed values greater than the specified
values?
L.T. Fuel
Trim: +20%
Go to
Step 5
Go to
Step 4
4
1. Review and record Tech 2 Failure Records data.
2. Clear the DTC P0171/P0174 and operate the
vehicle to duplicate the Failure Records conditions.
3. Monitor the Tech 2 “DTC” info for DTC P0174 while
operating the vehicle to duplicate the Failure
Records conditions.
4. Continue operating the vehicle until the DTC P0174
test runs.
5. Note the test result.
Does the Tech 2 indicate DTC P0174 failed this
ignition?
—
Go to
Step 5
The lean
condition is
not present.
If a
driveability
symptom still
exists, refer
to
Symptoms
section.
5
Was DTC P0171 also set?
—
Go to
Step 6
Go to
Step 15
6
Visually and physically inspect the vacuum hoses for
disconnects, splits, kinks, improper routing and
improper connections and repair any problem found.
Did your inspection reveal a problem requiring repair?
—
Verify repair
Go to
Step 7
7
Visually and physically inspect the crankcase
ventilation valve for proper installation and repair any
problem found (refer to
Crankcase Ventilation
System).
Did your inspection reveal a problem requiring repair?
—
Verify repair
Go to
Step 8
8
1. Inspect the MAF sensor inlet screen for damage or
for the presence of foreign objects which may
partially block the air flow sample through the MAF
sensor.
2. Correct any problem that is found as necessary.
Did your inspection of the MAF sensor reveal a
condition requiring repair?
—
Verify repair
Go to
Step 9
9
Start the engine and note the idle quality.
Is a high or unsteady idle being experienced?
—
Go to
Step 10
Go to
Step 11
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