DTC P0171 Fuel Trim System Lean Bank
1
Circuit
Description
The powertrain
control module (PCM) controls a Closed Loop air/fuel metering system in order
to provide the best possible combination of driveability,
fuel economy, and emission control. The PCM monitors the heated oxygen sensor
(HO2S) signal voltage and adjusts the fuel delivery based on the signal voltage
while in Closed Loop. A change made to the fuel delivery changes the long and
short term fuel trim values. The short term fuel trim values change rapidly in
response to the HO2S signal voltages. These changes fine tune the engine
fueling. The long term fuel trim values change in response to trends in the
short term fuel trim. The long term fuel trim makes coarse adjustments to
fueling in order to re-center and restore control to short term fuel trim. You
can use a scan tool in order to monitor the short and long term fuel trim. The
ideal fuel trim values are around 0 percent. A positive fuel trim value
indicates that the PCM is adding fuel in order to compensate for a lean
condition. A negative fuel trim value indicates that the PCM is reducing the
amount of fuel in order to compensate for a rich condition. If the PCM detects
an excessively Rich or Lean condition, the PCM sets a diagnostic trouble code
(DTC). The long term fuel trim diagnostic parameter is an
average of several of the long term speed load learn cells which the PCM
selects based on the engine speed and the engine load.
Conditions
for Running the DTC
- DTCs P0101, P0102, P0103, P0107,
P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0300,
P0335, P0336, P0351-P0358, P0401, P0404, P0405, P0410, P0412, P0418,
P0443, P0500, P0502, P0503, P1111, P1112, P1258, P1404, P1415, P1416 not
set.
- The engine coolant temperature is
between 50°C (122°F) and 115°C (239°F).
- The barometric pressure is greater
than 74 kPa.
- The mass air flow is between
5.0 g/s and 90 g/s.
- The manifold absolute pressure is
between 26 kPa and 90 kPa.
- The intake air temperature is
between -20°C (-4°F) and 90°C (194°F).
- The engine speed is between
400 RPM and 3,000 RPM.
- The TP sensor angle is less than
90%.
- The vehicle speed is less than
137 km/h (85 mph).
- The fuel level is greater than 10%.
Conditions
for Setting the DTC
- The average Long Term Fuel Trim cell
values are above a predetermined threshold.
- All the above conditions are present
for 6 seconds.
Action
Taken When the DTC Sets
- The PCM illuminates the Malfunction
Indicator Lamp (MIL) on the second consecutive ignition cycle that the
diagnostic runs and fails, if the diagnostic fails under the same
conditions (load, RPM, temperature, etc.) as the previous ignition cycle
that the test ran and failed.
- The first time the diagnostic fails,
the PCM records the operating conditions in Failure Records.
- The second consecutive ignition
cycle that this diagnostic fails [under the same conditions (load, RPM,
temperature, etc.) as the previous ignition cycle that the test ran and
failed], the PCM stores this information in
Freeze Frame. The PCM copies any data previously stored in Freeze Frame
and copies the data into the Failure Records. The PCM then overwrites the
Freeze Frame. The only exception to this is if a Misfire DTC was already recorded
in Freeze Frame. In this case, the Misfire data stays in Freeze Frame and
the PCM updates the Fuel Trim data in the Failure Records.
Conditions
for Clearing the MIL/DTC
- The PCM turns the MIL OFF after
three consecutive ignition cycles that the diagnostic runs and does not
fail within the same conditions that the DTC last failed.
Important
If
the last failure was during a non-typical driving condition, the MIL may remain
ON longer than the three ignition cycles. Review the Freeze Frame/Failure
Records for the last failure conditions.
- A History DTC clears after forty
consecutive warm-up cycles, if this or any other emission related
diagnostic does not report any failures.
- A last test failed (Current DTC)
clears when the diagnostic runs and does not fail.
- Use a scan tool in order to clear
the MIL/DTC.
Diagnostic
Aids
- This DTC sets if the engine runs out
of fuel.
- A fuel delivery malfunction causes
this DTC to set. Thoroughly inspect all items that cause a lean condition.
- For an intermittent condition, refer
to Symptoms
.
Test
Description
The numbers below refer
to the step numbers on the diagnostic table.
- This step determines
whether the fault is present. For any test that requires probing the PCM
or a component harness connector, use the Connector Test Adapter Kit J 35616-A .
Using this kit prevents damage to the harness connector terminals.
- Using the Freeze
Frame and/or Failure Records data may aid in locating an intermittent
condition. If you cannot duplicate the DTC, the information included in
the Freeze Frame and/or Failure Records data can help determine how many
miles since the DTC set. The Fail Counter and Pass Counter can also help
determine how many ignition cycles the diagnostic reported a pass and/or a
fail. Operate the vehicle within the same freeze frame conditions (RPM,
load, vehicle speed, temperature etc.) that you observed. This will
isolate when the DTC failed. For an intermittent condition, refer to Symptoms
.
- If DTC 174 is also
set indicates both banks of the engine are operating lean. Inspect the
items that would cause both banks to operate lean.
- A vacuum leak causes
DTCs P0171 and P0174 to set at the same time. Inspect all areas of the
engine for a vacuum leak. Also inspect the PCV valve for being the correct
one for this application. Make sure the engine oil fill cap is in place
and that it is tight. Ensure that the engine oil dip stick is fully
seated.
|
Step
|
Action
|
Value(s)
|
Yes
|
No
|
|
1
|
Did
you perform the Powertrain On-Board Diagnostic
(OBD) System Check?
|
--
|
Go
to Step 2
|
Go to A
Powertrain On Board Diagnostic (OBD) System Check
|
|
2
|
Important
If any DTCs are set, except
P0171 and P0174, refer to those DTCs before proceeding with this diagnostic.
- Install the scan tool.
- Idle the engine at the normal
operating temperature.
- Fuel system in Closed Loop.
- Monitor the LT FT Bn 1 display on the Fuel Trim Data List using the
scan tool.
Is
the LT FT less than the specified value indicated?
|
23% LT
|
Go
to Step 3
|
Go
to Step 4
|
|
3
|
- Turn ON the ignition leaving the
engine OFF.
- Review the Freeze Frame and/or
Failure Records data for this DTC and observe the parameters.
- Turn OFF the ignition for 15
seconds.
- Start the engine.
- Operate the vehicle within the
conditions required for this diagnostic to run, and as close to the
conditions recorded in Freeze Frame and/or Failure Records as possible.
Special operating conditions that you need to meet before the PCM will
run this diagnostic, where applicable, are listed in Conditions for
Running the DTC.
- Select the Diagnostic Trouble Code
(DTC) option and the Specific DTC option, then
enter the DTC number using the scan tool.
Does
the scan tool indicate that this diagnostic failed this ignition?
|
--
|
Go
to Step 4
|
Go to Diagnostic Aids
|
|
4
|
Is
DTC P0174 also set?
|
--
|
Go
to Step 5
|
Go
to Step 6
|
|
5
|
Visually/physically
inspect the following items:
Was
a concern found in any of the above areas?
|
--
|
Go
to Step 7
|
Go to Fuel
System Diagnosis
|
|
6
|
Visually/physically
inspect the following items:
- Bank 1 exhaust leaks, missing or
loose exhaust hardware.
- Bank 1 HO2S 1 is installed
securely and the electrical connector not contacting exhaust system or
ignition wires.
- Engine mechanical failure. Refer
to Base
Engine Misfire Diagnosis in Engine Mechanical 5.7L.
- Vacuum leaks that will only affect
bank 1, such as the intake manifold, the injector O rings, etc.
Was
a concern found in any of the above areas?
|
--
|
Go
to Step 7
|
Refer to Fuel
System Diagnosis
|
|
7
|
Repair
or replace any faulty items found. Is the action complete?
|
--
|
Go
to Step 8
|
--
|
|
8
|
- Select the Diagnostic Trouble Code
(DTC) option and the Clear DTC Information option using the scan tool.
- Idle the engine at the normal
operating temperature.
- Select the Diagnostic Trouble Code
(DTC) option and the Specific DTC option, then
enter the DTC number using the scan tool.
- Operate the vehicle within the
Conditions for Running the DTC as specified in the supporting text, if
applicable.
Does
the scan tool indicate that this test ran and passed?
|
--
|
Go
to Step 9
|
Go
to Step 2
|
|
9
|
Select
the Capture Info option and the Review Info option using the scan tool. Does
the scan tool display any DTCs that you have not diagnosed?
|
--
|
Go to the applicable
DTC table
|
System OK
|