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Isuzu D-Max / Isuzu Rodeo (TFR/TFS). Manual - part 849

6E–125

3.2L ENGINE DRIVEABILITY AND EMISSIONS

DTC P0171 –Fuel Trim System Lean

(Cont'd)

Step

Yes

Value(s)

Action

Check the fuel for excessive water, alcohol, or other
contaminants (see

Diagnosis in Engine Fuel for the

procedure) and correct the contaminated fuel condition
if present (see

Engine Fuel).

Was the fuel contaminated?

—

Verify repair

Go to

Step 12

1. Visually and physically inspect the ECM injector

grounds, power grounds and sensor grounds to
ensure that they are clean, tight, and in their proper
locations.

2. If a faulty ground condition is present, correct it as

necessary.

Did your inspection reveal a condition requiring repair?

—

Verify repair

Go to

Step 13

1. Disconnect the MAF sensor electrical connector.
2. Operate the vehicle in “closed loop” while

monitoring the “B1 Long Term Fuel Trim” displayed
on the Tech 2.

Does “BANK 1 S.T. FUEL TRIM” value decrease to
near the specified value?

Go to

Step 19

Go to

Step 14

Perform the procedure in the “Fuel System Pressure
Test” and repair fuel system problem if necessary.

Did Fuel System Pressure Test isolate a condition
requiring repair?

—

Verify repair

Go to

Step 15

Repair any problem that is found.

Did your inspection reveal a problem?

—

Verify repair

Go to

Step 16

Visually and physically inspect the Bank 1 exhaust
manifold for leaks and loose or missing hardware and
correct any problem found.

Did your inspection reveal a problem?

—

Verify repair

Go to

Step 17

Perform the “Injector Balance Test,” and correct any
problem found (refer to

Fuel Metering System).

Did Injector Balance Test isolate a problem?

—

Verify repair

Go to

Step 18

1. Visually and physically inspect the HO2S to ensure

that it is installed securely and that the HO2S pigtail
and wiring harness are not contacting the exhaust
or otherwise damaged.

2. If a problem is found, correct it as necessary.

Did your inspection reveal a problem?

—

Verify repair

Refer to

Diagnostic

Aids

Replace the MAF sensor.

Is the action complete?

—

Verify repair

—

6E–126 3.2L ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) P0172 (Flash DTC=45) Fuel Trim System Rich

060RW054

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 Engine Control Module ECM monitors the heated
oxygen sensors (HO2S) 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 ECM 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 ECM is reducing the amount of fuel delivered. If
an excessively rich condition is detected on Bank 1, the
ECM will set DTC P0172.
The ECM’s maximum authority to control long term fuel
trim allows a range between –15% (automatic
transmission) or –12 (manual transmission) and +20%.
The ECM’s maximum authority to control short term fuel
trim allows a range between –11% and +20%. The ECM
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

No Tech 2 test is being run.

None of the following was set: HO2S DTCs, (response,
transition, open, low volts, no activity), MAF DTCs,

TPS DTCs, BARO DTCs, IAT DTCs, canister purge
DTCs, injector circuit DTCs.

Engine coolant temperature is between 35

C and

120

Intake air temperature is below 50

Barometric pressure is more than 20 kpa.

Engine speed more than 600 RPM.

Fuel system is in “closed loop.”

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

Action Taken When the DTC Sets

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

The ECM 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

The ECM 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 P0172 will clear after 40 consecutive
warm-up cycles have occurred without a fault.

DTC P0172 can be cleared by using the Tech 2 “Clear
Info” function or by disconnecting the ECM battery
feed.

6E–127

3.2L ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Aids

Check for the following conditions:

Poor connection at ECM – 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
HO2S 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 P0172 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 P0172.

4. If the DTC P0172 test passes while the Failure

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

Diagnostic Aids or

Symptoms for additional information on diagnosing
intermittent problems.

DTC P0172 – Fuel Trim System Rich

Step

Action

Value(s)

Yes

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

—

Go to

Step 2

Go to

OBD

System

Check

Are any DTCs set other than P0172?

—

Go to the

applicable

DTC charts

and repair the

other DTCs

before

proceeding

with this chart

Go to

Step 3

1. Start the engine and operate the vehicle in “closed

loop.”

2. Observe “B1 Long Term Fuel Trim” display on the

Tech 2.

Is the displayed value more negative than the specified
value?

L.T. Fuel

Trim: –15%

(auto. trans.)

OR –12%

(man. trans.)

Go to

Step 5

Go to

Step 4

1. Review and record the Tech 2 Failure Records data.
2. Clear the DTC P0172 and operate the vehicle to

duplicate the Failure Records conditions.

3. Monitor the Tech 2 “Specific DTC” info for DTC

P0172 while operating the vehicle to duplicate the
Failure Records conditions.

4. Continue operating the vehicle until the DTC P0172

test runs and note test result.

Does the Tech 2 indicate DTC P0172 failed this
ignition?

—

Go to

Step 5

The rich

condition is

not present.

If a

driveability

symptom still

exists, refer

Symptoms.

Is DTC also set?

—

Go to

Step 6

Go to

Step 15

Visually and physically inspect the air filter element and
replace it if necessary.

Did the air filter require replacement?

—

Verify repair

Go to

Step 7

Visually and physically inspect the air intake duct for
collapse or restriction and repair if necessary.

Did your inspection reveal a condition requiring repair?

—

Verify repair

Go to

Step 8

6E–128 3.2L ENGINE DRIVEABILITY AND EMISSIONS

DTC P0172 – Fuel Trim System Rich

(Cont'd)

Step

Yes

Value(s)

Action

Inspect the MAF sensor inlet screen for damage or for
the presence of foreign objects which may partially
block air flow through the screen and correct any
problem found.

Did your inspection of the MAF sensor reveal a
condition requiring repair or replacement?

—

Verify repair

Go to

Step 9

Start the engine and note the idle quality.

Is a low or unsteady idle being experienced?

—

Go to

Step 10

Go to

Step 11

1. Ignition “OFF.”
2. Physically inspect the throttle body bore, throttle

plate, and IAC passages for coking and foreign
objects.

3. If a problem was found, repair as necessary.

Did your inspection reveal a condition requiring repair?

—

Verify repair

Go to

Step 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

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 21

1. Disconnect the MAF sensor electrical connector.
2. Operate the vehicle in “closed loop” while

monitoring the “Long Term Fuel Trim” and “Short
Term Fuel Trim” display on the Tech 2.

Did both values change to near the specified value?

Go to

Step 22

Go to

Step 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 15

1. Ignition “ON,” engine “OFF.”
2. Connect a test light between the harness connector

terminals of canister purge solenoid.

Is the test light on?

—

Go to

Step 16

Go to

Step 19

Check for short to ground in the wire (red/blue)
between the canister purge solenoid and ECM terminal
A-15.

Was there a short to ground?

—

Go to

Step 17

Go to

Step 18

Repair the short to ground.

Is the action complete?

—

Verify repair

—

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