Buick Regal: DTC P0171 or P0172
Diagnostic Instructions
- Perform the Diagnostic System Check - Vehicle prior to using this
diagnostic procedure.
- Review Strategy Based Diagnosis for an overview of the diagnostic
approach.
- Diagnostic Procedure Instructions provides an overview of each
diagnostic category.
DTC Descriptors
DTC P0171
Fuel Trim System Lean
DTC P0172
Fuel Trim System Rich
Circuit/System Description
The engine control module (ECM) controls a Closed Loop air/fuel metering
system in order to provide
the best possible combination of driveability, fuel economy, and emission
control. The ECM 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 recenter
and restore control to short term fuel trim. The ideal fuel trim values are
around 0 %. A positive
fuel trim value indicates that the ECM is adding fuel in order to compensate for
a lean condition. A
negative fuel trim value indicates that the ECM is reducing the amount of fuel
in order to compensate
for a rich condition.
Conditions for Running the DTC
- DTCs P0030, P0053, P0101, P0102, P0103, P0106, P0107, P0108, P0131 -
P0135, P015A,
P015B, P0178, P0179, P0201 - P0204, P0236, P0237, P0238, P0261, P0262,
P0264, P0265,
P0267, P0268, P0270, P0271, P0300 - P0304, P0411, P0442, P0455, P0458,
P0496, P0506,
P0507, P1248, P1249, P124A, P124B, P2147, P2148, P2150, P2151, P2153, P2154,
P2156,
P2157, P2227, P2228, P2229, P2230, P2269, P2440, P2444, or P2A00 are not
set.
- The engine is in Closed Loop status.
- The catalyst monitor diagnostic intrusive test, post 02 diagnostic
intrusive test, device control, and
evaporative emission leak test are not active.
- The engine coolant temperature (ECT) is between -20 and +130ºC (-4 and
+266ºF).
- The intake air temperature (IAT) is between -20 and +150ºC (-4 and
+302ºF).
- The manifold absolute pressure (MAP) is between 15 - 255 kPa (2.2 - 37
psi).
- The engine speed is between 400 - 6, 600 RPM.
- The mass air flow (MAF) is between 1 - 512 g/s.
- The barometric pressure (BARO) is greater than 70 kPa (10.2 psi).
- The fuel level is greater than 10 %.
- This diagnostic runs continuously when the above conditions have been
met.
Conditions for Setting the DTC
- The average long term fuel trim weighted average value is greater 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 and P0172 are Type B DTCs.
Conditions for Clearing the MIL/DTC
TCs P0171 and P0172 are Type B DTCs.
Diagnostic Aids
- The normal Short Term Fuel Trim and Long Term Fuel Trim parameters
should be between +10
and -10 % with 0 % the optimum, with the engine running at operating
temperature.
- Any un-metered air into the engine causes this DTC to set. Thoroughly
inspect all areas of the
engine for vacuum leaks.
- A MAF sensor condition can cause this DTC without setting a MAF DTC. If
there is a MAF
sensor condition, the MAF sensor parameters will appear to be within range.
- Verify that the air filter is the correct one for this application.
Verify that the engine oil fill cap is
in place and that it is tight. Verify that the engine oil dip stick is fully
seated.
- Certain aftermarket air filters may cause a DTC to set.
- Certain aftermarket air induction systems or modifications to the air
induction system may cause a
DTC to set.
- Certain aftermarket exhaust system components may cause a DTC to set.
Reference Information
Component View Reference
Powertrain Component Views
Electrical Information Reference
- Circuit Testing
- Connector Repairs
- Testing for Intermittent Conditions and Poor Connections
- Wiring Repairs
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
1. Ignition ON.
2. Verify no other DTCs are set.
- If any other DTCs are set
Refer to Diagnostic Trouble Code (DTC) List - Vehicle for further
diagnosis.
- Go to next step: If no other DTCs are set
3. Verify DTC P0171 or P0172 is not set.
Refer to Circuit/System Testing.
- Go to next step: If no DTC is set
4. Operate the vehicle within the Conditions for Running the DTC. You may
also operate the vehicle
within the conditions that you observed in the Freeze Frame/Failure Records
data.
5. Verify DTC P0171 or P0172 is not set.
Refer to Circuit/System Testing.
- Go to next step: If none of the DTCs set
6. All OK.
Circuit/System Testing
1. Ignition ON.
2. Verify the manifold absolute pressure sensor is within the range specified
for your altitude. Refer
to Altitude Versus Barometric Pressure.
- If not within the specified range
Refer to DTC P0106
- Go to next step: If within the specified range
3. Engine running at the operating temperature.
4. Verify the Long Term Fuel Trim parameter is between -10 % and +10 %.
If greater than +10 %
- Ignition OFF.
- Inspect for the conditions listed below:
- Mass air flow (MAF) sensor signal skewed. If the Short Term Fuel
Trim parameter
changes greater than 20 % when the MAF sensor is disconnected, refer to
DTC
P0101.
- Fuel contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis.
- Missing, restricted, or leaking exhaust components. Refer to
Symptoms - Engine Exhaust.
- Malfunctioning fuel injectors. Refer to Fuel Injector Diagnosis.
- Split, kinked or improperly connected vacuum hoses.
- Insufficient fuel in the tank
- Low fuel pressure. Refer to Fuel System Diagnosis.
- Vacuum leaks at the intake manifold, the throttle body, and the
injector O-rings.
- Leaks in the air induction system and the air intake ducts
- Missing air filter element
- Cracked EVAP canister
- Evaporative pipes obstructed or leaking
- Leaks in the crankcase ventilation system. Refer to Crankcase
Ventilation System Inspection/Diagnosis.
- If a condition is found, repair as necessary.
- If no condition is found, inspect the engine for a mechanical
condition. Refer to Symptoms - Engine Mechanical.
- Ignition OFF.
- Inspect for the conditions listed below:
- Mass air flow (MAF) sensor signal skewed. If the Short Term Fuel
Trim parameters
for both banks changes greater than 20 % when the MAF sensor is
disconnected, refer
to DTC P0101.
- Fuel contamination - Refer to Alcohol/Contaminants-in-Fuel
Diagnosis.
- Missing, restricted, or leaking exhaust components - Refer to
Symptoms - Engine Exhaust.
- Malfunctioning fuel injectors - Refer to Fuel Injector Diagnosis
- Collapsed or restricted air intake duct
- Excessive fuel pressure - Refer to Fuel System Diagnosis
- Dirty or restricted air filter
- Objects blocking the throttle body
- Improper operation of the evaporative emissions control system
- Excessive fuel in the crankcase - Change engine oil as necessary and
inspect for the
following:
G18 High Pressure Fuel Pump=Leaking
Q17 Fuel Injector=Leaking - Refer to Fuel Injector Diagnosis
- If a condition is found, repair as necessary.
- If no condition is found, inspect the engine for a mechanical condition.
Refer to Symptoms - Engine Mechanical.
- Go to next step: If between -10 % and +10 %
5. Operate the vehicle within the Conditions for Running the DTC. You may
also operate the vehicle
within the conditions that you observed in the Freeze Frame/Failure Records
data.
6. Verify DTC P0171 or P0172 is not set.
Refer to conditions listed above.
- Go to next step: If none of the DTCs set
7. All OK.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the repair.
Perform the scan tool Fuel Trim Reset after completing the repair.
READ NEXT:
Diagnostic Instructions
Perform the Diagnostic System Check - Vehicle prior to using this
diagnostic procedure.
Review Strategy Based Diagnosis for an overview of the diagnostic
approach.
Diag
Diagnostic Instructions
Perform the Diagnostic System Check - Vehicle prior to using this
diagnostic procedure.
Review Strategy Based Diagnosis for an overview of the diagnostic
approach.
Diag
Diagnostic Instructions
Perform the Diagnostic System Check - Vehicle prior to using this
diagnostic procedure.
Review Strategy Based Diagnosis for an overview of the diagnostic
approach.
Diag
SEE MORE:
NOTE: Review the system description and operation in order to
familiarize yourself
with the system functions. Refer to Power Steering System Description and
Operation (Electronic Power Steering).
Visual/Physical Inspection
Inspect for aftermarket devices which could affect the operation of the
Removal Procedure
1. Drain the cooling system.
2. Front Bumper Fascia - Remove.
3.
Hood Primary Latch Mount Panel Bracket (3) - Remove.
4. Recover the refrigerant.
5.
Air Conditioning Condenser Bracket (1) - Remove.
6. Transmission Fluid Cooler Inlet and Outlet Pipe Retainer @ Engine Cooler