DTC P0171 or P0172 (LDD)
Diagnostic Instructions
DTC Descriptor
DTC P0171 00: Fuel Trim System Lean |
DTC P0172 00: Fuel Trim System Rich |
Circuit/System Description
The engine control module (ECM) controls the air/fuel metering
system in order to provide the best possible combination of
driveability, fuel economy, and emission control. Fuel delivery is
controlled differently during open loop and closed loop. During
open loop, the ECM determines fuel delivery based on sensor signals
without heated oxygen sensor (HO2S) input. During closed loop, the
ECM adds HO2S inputs and level of purge to calculate the short and
long term fuel trim adjustments. If the HO2S indicates a lean
condition, the fuel trim values will be above 0%. If the HO2S
indicates a rich condition, the fuel trim values will be below 0%.
The short term fuel trim values change rapidly in response to the
HO2S voltage signals. The long term fuel trim makes rough
adjustments in order to maintain an optimal air/fuel ratio. A block
of memory cells contain information arranged in combinations of
engine RPM and engine load for a full range of vehicle operating
conditions. The long term fuel trim diagnostic is based on an
average of cells currently being used. The ECM selects the cells
based on engine speed and load. The fuel trim diagnostic will
conduct a test to determine if a rich malfunction actually exists
or if excessive vapor from the evaporative emission (EVAP) canister
is causing a rich condition.
The heating elements inside each heated oxygen sensor (HO2S)
heat the sensor to bring the sensor up to operating conditions
faster. This allows the system to enter closed loop earlier and the
control module to calculate the air-to-fuel ratio sooner.
The heated oxygen sensor (HO2S) utilizes the following
circuits:
• |
A low reference circuit
|
• |
An ignition voltage
circuit |
• |
A heater control
circuit |
Conditions for Running the DTC
• |
DTCs P0101 00, P0102 00, P0103
00, P0106 00, P0107 00, P0108 00, P0112 00, P0113 00, P0201 00,
P0202 00, P0203 00, P0204 00, P0300 00, P0301 00, P0302 00, P0303
00, P0304 00, P0442 00, P0443 00, P0449 00, P0451 00, P0452 00,
P0453 00, P0454 00, P0455 00, P0461 00, P0462 00, P0463 00, P0464
00, P0496 00, P0506 00, and P0507 00 are not set. |
• |
Where applicable DTCs P2270
00, P2271 00, P2272 00, P2A01 00 are not set. |
• |
The loop status parameter
indicates closed. |
• |
The fuel trim learn is
enabled. |
• |
The engine coolant temperature
(ECT) is between -38 to +1 530°C (-36.4 to +266°F).
|
• |
The intake air temperature
(IAT) is between -38 to +150°C (-36.4 to +302°F).
|
• |
The manifold absolute pressure
(MAP) is between 15-255 kPa (2-37 PSI). |
• |
The vehicle speed is less than
134 km/h (83 MPH). |
• |
The engine speed is between
400-6 000 RPM. |
• |
The engine airflow is between
1-512 g/s. |
• |
The fuel level is greater than
10%. |
• |
The barometric pressure (BARO)
is more than 70 kPa. |
• |
DTCs P0171 00 and P0172 00 run
continuously when the above conditions have been met. |
Conditions for Setting the DTC
• |
The average long term weighted
average value is more or less than a calibrated value. |
• |
The above condition is present
for approximately 3 min after the conditions for running the DTC
have been met. |
Action Taken When the DTC Sets
DTCs P0171 00, P0172 00 are Type B DTCs.
Conditions for Clearing the DTC
DTCs P0171 00, P0172 00 are Type B DTCs.
Diagnostic Aids
• |
On vehicles equipped with a
vacuum brake booster, rapid brake pedal cycling may imitate a
vacuum leak. |
• |
The system will become lean if
a fuel injector is not supplying enough fuel. |
• |
A lean condition may be
present during high fuel demand due to a fuel pump that does not
deliver enough fuel, a plugged fuel filter, or a restricted fuel
pipe. |
• |
The system will become rich if
a fuel injector is supplying too much fuel. |
• |
An exhaust system leak that
may not be audible but can cause a DTC to set. |
• |
A mass air flow (MAF) sensor
that is installed incorrectly can set this these DTCs. |
Reference Information
Schematic Reference
Engine Controls Schematics
Connector End View Reference
Component Connector End Views
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
Note: Disregard any
transmission symptoms, antilock brake system (ABS) indicators, and
traction control system indicators until any fuel trim faults are
repaired. A fuel trim fault may cause default actions such as harsh
shifts and illumination of the ABS or traction control
indicators.
1. |
Verify that other DTCs are not
set. |
2. |
Allow the engine to reach
operating temperature. With the engine running, observe the B52A
Heated Oxygen Sensor 1 parameter with a scan tool. The B52A Heated
Oxygen Sensor 1 value should vary from approximately 40 mV to
approximately 900 mV, and respond to fueling changes. |
|
Note: The EVAP purge
enablement may cause the fuel trim to be momentarily outside the
normal range.
|
3. |
The normal short term fuel
trim parameter should be between +5 to -5%, with near 0% the
optimum, with the engine running at operating temperature.
|
4. |
The long term fuel trim
parameter should be between +5 to -5%, with near 0% the optimum,
with the engine running at operating temperature. |
5. |
Operate the vehicle within the
conditions for running the DTC. You may also operate the vehicle
within the conditions that you observed from the freeze
frame/failure records data. |
Circuit/System Testing
P0171 00
Allow the engine to reach operating temperature. With the engine
running, observe the Long Term Fuel Trim parameter with a scan
tool. The value should be between +5 to -5%.
If not within the specified range, verify none of the following
conditions exist.
• |
With the engine idling,
observe the MAF sensor parameter. The MAF sensor parameter should
be between 2-6 g/s at idle. |
⇒ |
If the MAF sensor parameter is not between 2-6 g/s
at idle, refer to
DTC P0101 . |
• |
Vacuum hoses for splits,
kinks, and improper connections |
• |
Insufficient fuel in the
tank |
• |
Missing, loose, or leaking
exhaust components from the B52A Heated Oxygen Sensor 1
forward-Refer to
Symptoms - Engine Exhaust . |
• |
Vacuum leaks at the intake
manifold, the Q38 Throttle Body, and the Q17 Fuel Injector
O-rings |
• |
The air induction system and
the air intake ducts for leaks or for a missing air filter
element |
• |
A cracked EVAP canister
|
• |
Evaporative pipes obstructed
or leaking |
• |
The crankcase ventilation
system for leaks |
• |
The B52A Heated Oxygen Sensor
1 for improper installation and for electrical wires or connectors
that may have contacted the exhaust system |
• |
The B52A Heated Oxygen Sensor
1 signal circuit open, shorted to ground, or shorted to the low
reference circuit |
P0172 00
Allow the engine to reach operating temperature. With the engine
running, observe the Long Term Fuel Trim parameter with a scan
tool. The reading should be between +5 to -5%.
If not within the specified range, inspect for the following:
• |
With the engine idling and the
transmission in the park or neutral position, observe the MAP
Sensor parameter. The MAP Sensor parameter should be between 19-42
kPa. |
⇒ |
If the MAP Sensor parameter is not between 19-42
kPa (2.8-6.0 PSI), refer to
DTC P0106 . |
• |
With the engine idling,
observe the MAF Sensor parameter. The MAF Sensor parameter should
be between 2-6 g/s at idle. |
⇒ |
If the MAF Sensor parameter is not between 2-6 g/s
at idle, refer to
DTC P0101 . |
• |
Vacuum hoses for splits,
kinks, and improper connections |
• |
The air intake duct for being
collapsed or restricted |
• |
The air filter for being dirty
or restricted |
• |
Objects blocking the throttle
body |
• |
Excessive fuel in the
crankcase due to leaking fuel injectors |
• |
The HO2S for improper
installation and for electrical wires or connectors that may have
contacted the exhaust system |
• |
The HO2S signal circuit
shorted to voltage |
Repair or replace as necessary.
Repair Instructions
Repair Verification
|
Note: After repairs,
use the scan tool fuel trim reset function in order to reset the
long term fuel trim values.
|
1. |
Install any components or
connectors that have been removed or replaced during
diagnosis. |
2. |
Perform any adjustment,
programming, or setup procedures that are required when a component
or module is removed or replaced. |
3. |
Turn ON the ignition, with the
engine OFF. |
|
Note: Do not clear
codes with the engine running. DTCs may reset in the same ignition
cycle.
|
5. |
Turn OFF the ignition for 60
s. |
7. |
Duplicate the conditions for
running the DTC and use freeze frame/failure records, if
applicable, in order to verify the DTC does not reset. If the DTC
resets or another DTC is present, refer to
Diagnostic Trouble Code (DTC) List - Vehicle . |
8. |
In order to ensure that the
performance of the catalyst has not been affected by the fault that
set this DTC, perform the repair verification for DTC P0420 00.
Refer to
DTC P0420 . |
|