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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 the 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 (FT) values. The short term FT values change rapidly in response to the HO2S voltage signals. These changes fine tune the engine fuelling. The long term FT makes coarse adjustments in order to maintain an optimum air/fuel ratio. The ideal FT values are around zero percent. A positive FT value indicates that the ECM is adding fuel in order to compensate for a lean condition. A negative FT 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, P0112, P0113, P0114, P0121, P0122, P0123, P0131, P0132, P0133, P0134, P0135, P0201, P0202, P0203, P0204, P0300, P0301, P0302, P0303, P0304, P0442, P0455, P0458, and P2A00 are not set.
    • The engine is in Closed Loop.
    • The catalyst monitor intrusive test, post HO2S intrusive test, device controls and EVAP leak test are not active.
    • The engine coolant temperature (ECT) is between -38 to +130°C (-36.4 to +266°F).
    • The inlet air temperature (IAT) is between -20 to +150°C (-4 to +302°F).
    • The manifold absolute pressure (MAP) is between 15-255 kPa (2-37 PSI).
    • The engine speed is between 400-6,100 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.
    • These DTCs run continuously when the above conditions have been met.

Conditions for Setting the DTC
    • The long term FT 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 and P0172 are type B DTCs.

Conditions for Clearing the DTC

DTCs P0171 and P0172 are type B DTCs.

Diagnostic Aids
    • The system will become lean if a fuel injector is not supplying enough fuel -- P0171.
    • 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 -- P0172.
    • The system will become rich if a fuel injector is supplying too much fuel -- P0172.
    • An exhaust system leak that may not be audible but can cause a DTC to set.
    • Certain aftermarket air filters may cause a DTC to set.
    • Certain aftermarket 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

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Hybrid Modes of Operation Description

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. Vehicle in Service Mode, verify that other DTCs are not set.
    2. ⇒If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .
  2. Observe the MAP Sensor parameter. The MAP Sensor pressure should be within the range specified for your altitude. Refer to Altitude Versus Barometric Pressure .
    3. ⇒If not within the specified range, refer to DTC P0106 .
  3. Vehicle ON, engine speed between 1,375--1,425 RPM, normal operating temperature. Verify the scan tool MAF Sensor parameter is between 1,800-2,400 Hz.
    4. ⇒If not within the specified range, refer to DTC P0101 .
  4. Observe the Long Term Fuel Trim parameter with a scan tool. The reading should be between -19 to +24%.
    5. ⇒If not within the specified range, verify none of the following conditions exist:

    P0171

    • Vacuum hoses for splits, kinks, and improper connections.
    • Insufficient fuel in the tank.
    • Low fuel pressure, refer to Fuel System Diagnosis .
    • Ethanol concentration greater than 15%, refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Fuel contamination, refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Malfunctioning fuel injectors, refer to Fuel Injector Solenoid Coil Test .
    • Missing, loose, or leaking exhaust components from the Heated Oxygen Sensor 1 forward, refer to Symptoms - Engine Exhaust .
    • Vacuum leaks at the inlet manifold, the throttle body, and the fuel injector O-rings.
    • The air induction system and the air inlet 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.

    P0172

    • Vacuum hoses for splits, kinks, and improper connections
    • The air inlet 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 EVAP control system for improper operation, refer to Evaporative Emission Control System Diagnosis .
    • Excessive fuel pressure, refer to Fuel System Diagnosis .
    • Malfunctioning fuel injectors, refer to Fuel Injector Solenoid Coil Test .
    • Fuel contamination, refer to Alcohol/Contaminants-in-Fuel Diagnosis .
  5. If all conditions test normal, test the engine for a mechanical condition. Refer to Symptoms - Engine Mechanical
  6. Operate the vehicle within the conditions for running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the freeze frame/failure records data.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

   


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