Chevrolet Trax: 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 re-center 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, P0178, P0179, P0201-
P0204, 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, or P2444 are
not set.
- The engine is in Closed Loop status.
- The catalyst monitor diagnostic intrusive test, post 02 diagnostic
intrusive test, and evaporative emissions
system leak test are not active.
- The engine coolant temperature (ECT) is between -20ºC and +130ºC (-4ºF
and +266ºF).
- The intake air temperature (IAT) is between -20ºC and +150ºC (-4ºF and
+302ºF).
- The manifold absolute pressure (MAP) is between 18-253 kPa (2.6-36.7 psi).
- The engine speed is between 400-6,100 RPM.
- The mass air flow (MAF) is between 1.5-505 g/s.
- The barometric pressure (BARO) is greater than 70 kPa (10.2 psi).
- The fuel level is greater than 10 % and no fuel sensor fault is present.
- 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
DTCs P0171 and P0172 are Type B DTCs.
Diagnostic Aids
- Allow the engine to reach operating temperature. With the engine running,
observe the HO2S parameter
with a scan tool. The HO2S value should vary from approximately 40 mV to
approximately 900 mV, and
respond to fueling changes.
- 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.
- Inspect the air filter for being the correct one for this application.
Make sure 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 (LUV) ,
Powertrain Diagnostic Trouble
Code (DTC) Type Definitions (2H0)
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Ignition ON.
- Verify no other DTCs are set.
- If any other DTCs are set
Refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.
- Verify DTC P0171 or P0172 is not set.
Refer to Circuit/System Testing.
- 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.
- Verify DTC P0171 or P0172 is not set.
Refer to Circuit/System Testing.
- All OK.
Circuit/System Testing
- Ignition ON.
- 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
- If within the specified range
- Engine running at the operating temperature.
- Verify the Long Term Fuel Trim parameter is between -28.5 % and +33 %.
- 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 (LUJ) , Fuel System
Diagnosis (LUV) .
- 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.
- If a condition is found, repair as necessary.
- If no condition is found, test 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 (LUJ) , Fuel
System Diagnosis
(LUV)
- Dirty or restricted air filter
- Objects blocking the throttle body
- Improper operation of the evaporative emissions control system
- Excessive fuel in the crankcase. Change the engine oil as necessary.
- If a condition is found, repair as necessary.
- If no condition is found, test the engine for a mechanical condition.
Refer to
Symptoms - Engine Mechanical .
- If between -28.5 % and +33 %
- All OK.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the repair
Reset the fuel trim 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:
Special Tools
BO-6392 Flanging Tool Kit
BO-6396 Bonding Pliers
For equivalent regional tools, refer to Special Tools.
NOTE: According to different corrosion warranties, only the
regional mandatory joining
methods are allowed.
Removal Procedure
WARNING: Refer to Glass and Sheet Metal Handling Wa
Removal Procedure
WARNING: Refer to Approved Equipment for Collision Repair Warning .
Disable the SIR system. Refer to SIR Disabling and Enabling .
Disconnect the negative battery cable. Refer to Battery Negative Cable
Disconnection and
Connection .
Remove all related panels and components.