Isuzu Trooper (2000 year). Service manual — part 321

6E–413

TROOPER 6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) P1171 Fuel System Lean During Acceleration

D06RY00175

Circuit Description

The powertrain control module (PCM) internal circuitry
can identify if the vehicle fuel system is capable of
supplying adequate amounts of fuel during heavy
acceleration (power enrichment). The PCM monitors the
voltage of the oxygen sensor during power enrichment.
When a power enrichment mode of operation is
requested during “closed loop” operation (by heavy
acceleration), the PCM will provide more fuel to the
engine. Under these conditions the PCM should detect a
“rich” condition (high oxygen sensor voltage). If this “rich”
exhaust is not detected at this time, a DTC P1171 will set.
A plugged fuel filter, restricted fuel line, restricted in-tank
filter or defective fuel pump can prevent adequate
amounts of fuel from being supplied during power
enrichment mode.

Conditions for Setting the DTC

D

No related DTCs.

D

Engine is operating in “closed loop power enrichment”
mode for 3 seconds.

D

Engine coolant temperature is above 60

°

C (140

°

F).

D

While in “power enrichment” mode the oxygen sensor
voltage remains below 400 mV for 3 seconds.

Action Taken When the DTC Sets

D

The PCM will illuminate the malfunction indicator lamp
(MIL) the first 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 P1171 will clear after 40 consecutive
warm-up cycles have occurred without a fault.

D

DTC P1171 can be cleared by using the Tech 2 “Clear
Info” function or by disconnecting the PCM battery
feed.

Diagnostic Aids

D

A restricted fuel filter or fuel line, restricted in-tank filter,
or a defective fuel pump may supply adequate
amounts of fuel at idle, but may not be able to supply
enough fuel during heavy acceleration.

D

Water or alcohol in the fuel may cause low HO2S
voltage during acceleration.

D

Check for faulty or plugged fuel injector(s).

D

Check for low fuel.

6E–414

TROOPER 6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

Test Description

Number(s) below refer to the step number(s) on the
Diagnostic Chart.
4. When the engine is idling or at steady cruise, the

HO2S voltage should vary from between
approximately 100 mV to 900 mV. It is possible to
measure a satisfactory fuel pressure at idle even
though the pressure may drop at high flow
requirements. It may be necessary to watch fuel
pressure at high engine load.

5. Wrap a shop towel around the fuel pressure

connector to absorb any small amount of fuel
leakage that may occur when installing gauge.
Ignition “ON,” pump pressure should be 280-320
kPa.

7. Add Caution, Use correct pliers so damage to fuel

lines will not occur.

6E–415

TROOPER 6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

DTC P1171 – Fuel System Lean During Acceleration

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 component-related DTCs set?

—

Go to

component

DTC charts

Go to

Step 3

3

1. Check the vehicle’s fuel tank for an adequate

amount of fuel.

2. Add fuel to the vehicle’s fuel tank if the tank is almost

empty.

Was fuel added to the vehicle’s fuel tank?

—

Go to

Step 4

Go to

Step 5

4

1. Place the transmission in park.
2. Using a Tech 2, observe HO2S 1 voltage while

running warm engine 75

°

C-95

°

C (167

°

F-203

°

F) at

1200 RPM.

3. HO2S 1 voltage should vary within the specified

range.

4. Quickly open the throttle halfway for a few seconds.

Did the voltage suddenly rise toward the high end of the
specified range?

100-900 mV

Go to

Fuel

System

Electrical Test

Go to

Step 5

5

1. Disconnect the fuel pump relay and crank the

engine to relieve the fuel pressure.

2. Install the fuel pressure gauge.
3. Start the engine and idle at normal operating

temperature.

4. Disconnect the vacuum line going to the fuel

pressure regulator.

With the engine running, is the fuel pressure within the
specified range?

280-325 kPa

(41-46 psi)

Go to

OBD

System

Check

Go to

Step 6

6

Check for restricted fuel lines or restricted in-line filter.

Was a problem found?

—

Verify repair

Go to

Step 7

7

1. Ignition “OFF.”
2. Remove the fuel pump relay and replace it with a

fused jumper which will connect the relay’s battery
terminal to the terminal leading to the fuel pump
fuse.

3. While the fuel pump is operating, use pliers to slowly

close the return line (do not exceed the first
specified value).

Using the pliers to restrict the return line, can the fuel
pressure be manipulated to exceed the second
specified value?

414 kPa

(60 psi)

325 kPa

(46 psi)

Go to

Diagnostic

Aids

Go to

Step 8

8

Check for:

D

Faulty fuel pump

D

Restricted fuel pump strainer (sock)

D

Incorrect fuel pump

D

Incorrect fuel being used

D

Hot fuel

Is the action complete?

—

Verify repair

—

6E–416

TROOPER 6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC)

P1220 Throttle Position Senser2 (TPS2) Circuit Fault

D06RY00088

Circuit Description

D

The throttle position (TP2) sensor circuit provides a
voltage signal relative to throttle blade angle.

The throttle blade angle will vary about 92 % at
closed throttle to about 8 % at wide open throttle
(WOT).

This code detects a continuous short to ground or
high in either the cicuit or the sensor.

Conditions for setting the DTC

D

The Ignition is “ON”.

D

The throttle blade angle is less than 2.5 % or more tnan
97.5 % for 18 failres within 500 test samples (15.6m
sec).

Action Taken When the DTC Sets

D

The PCM will store condition 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 condtion is no longer present.

D

A history DTC P1120 will clear after 40 consecutive trip
cycle during which the warm up cycles have occurred
without a fault.

D

DTC P1120 can be cleared using the Tech2 “Clear Info”
function or by disconnecting the PCM battery feed.

Diagnostic Aids

An intermittent may be caused by the following:

D

Poor connectons.

D

Mis routed harness.

D

Rubbed through wire insulation.

D

Broken wire inside the insulation.

Check for the following conditions:

D

The MAP sensor shares a 5 Volt reference with the
Fuel Tank Pressure.If these codes are also set, it could
indicate a problem with the 5 Volt reference circuit.

D

The MAP sensor shares a ground with the Fuel Tank
Pressure,the ECT sensor,and the Transmission Fluid

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
TP sensor 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. If DTC P1120 cannot be duplicated,the
information included in the Faillure Records data
can be useful in determined vehicle mileage since
the DTC was last set.