DTC P0171 or P0172 - LLU
Diagnostic Instructions
DTC Descriptors
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 vapour 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) utilises 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 DTC's. |
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 as
illumination of the antilock brake system (ABS), and traction
control system indicators.
- Engine running, observe the DTC information with a
scan tool. Verify that other DTCs are not set.
- Ignition ON, observe the scan tool MAP sensor pressure
parameter and compare the reading on the scan tool to the
barometric pressure table. Refer to
Altitude Versus Barometric Pressure .
⇒ |
If the MAP sensor pressure is not within the range
specified for your altitude. |
- Engine running, observe the scan tool MAF Sensor
parameter. The MAF sensor parameter should be between 2-6 g/s
at idle.
- Engine running, observe the scan tool Throttle
Position sensor percentage parameter. The reading should be less
than 10%.
- Observe the scan tool HO2S Sensor 1 voltage
parameter. The reading should fluctuate within
200-800 mV.
⇒ |
If not within the specified range, refer to
DTC P0131, P0132, P0137, or P0138 and
DTC P0133, P0134, P0140, P1133, P2270, P2271, or P2A00 . |
- Engine at normal operating temperature, observe the
scan tool Long Term Fuel Trim parameter. The reading should be
between -5 to +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
Note: You must perform the
circuit/system verification before proceeding with circuit/system
testing.
- Verify none of the following conditions exist:
• |
Splits, kinks, or improper connections at the
vacuum hoses |
• |
Leaks in the air induction system between the
turbocharger outlet and the throttle body inlet, including the air
cooler. |
• |
Vacuum leaks at the intake manifold, throttle
body, and injector O-rings. |
• |
Leaking crankcase ventilation system. |
• |
The air intake duct for being collapsed or
restricted possibly by a restricted air filter. |
• |
Excessive fuel in the crankcase. |
• |
The incorrect operation of the evaporative
emissions control system. |
- If all conditions test normal, test the engine for a
mechanical condition. Refer to
Symptoms - Engine Mechanical .
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic
procedure.
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