P0171 Fuel Trim System Lean Bank - Isuzu 2000 Trooper Workshop Manual

Diagnostic Trouble Code (DTC) P0171 Fuel Trim System Lean Bank 1
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
D No Tech 2 test is being run.
D 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.
TROOPER 6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS
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.
D Ignition voltage is above 9.5 volts.
D Fuel system is in "closed loop."
D Canister purge duty cycle is greater than 0% if on.
Action Taken When the DTC Sets
D The PCM will illuminate the malfunction indicator lamp
(MIL) after the second consecutive trip in which 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 P0171 will clear after 40 consecutive
warm-up cycles have occurred without a fault.
6E–225
D06RY00171