GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2006 🢒 Epica 🢒 Engine 🢒 Engine Controls - 2.5L (LBK) 🢒 DTC P0171, P0172, P0174, or P0175

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 provide an overview of each diagnostic category.

DTC Descriptors

DTC P0171: Fuel Trim System Lean Bank 1

DTC P0172: Fuel Trim System Rich Bank 1

DTC P0174: Fuel Trim System Lean Bank 2

DTC P0175: Fuel Trim System Rich Bank 2

Circuit 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 percent. 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. The fuel trim cells are based on the engine speed and load.

Conditions for Running the DTC
    • DTCs P0030, P0031, P0032, P0036, P0037, P0038, P0050, P0051, P0052, P0056, P0057, P0058, P0102, P0103, P0107, P0108, P0111, P0112, P0113, P0114, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0130, P0131, P0132, P0133, P0134, P0136, P0137, P0138, P0139, P0140, P0150, P0151, P0152, P0153, P0154, P0156, P0157 P0158, P0159, P0160, P0221, P0222, P0223, P0230, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0276, P0277, P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0335, P0336, P0337, P0340, P0341, P0351, P0352, P0353, P0354, P0355, P0356, P0443, P0458, P0459, P0638, P2111, P2112, and P2119 are not set.
    • The fuel system is in closed loop.
    • The engine speed is greater than 608 RPM
    • The mass air flow (MAF) is greater than 49 mg/stk.
    • The engine coolant temperature (ECT) is greater than 75°C (167°F).
    • The barometric pressure (BARO) is greater than 75 kPa.
    • The intake air temperature (IAT) sensor is greater than -10°C (14°F).
    • The EVAP canister has been purging for more than 240 seconds, then it is disabled for 60 seconds.
    • The DTCs run continuously when the above conditions are met.

Conditions for Setting the DTC

P0171 or P0174

The average long term fuel trim cell values are more than 30 percent for 10 seconds.

P0172 or P0175

The average long term fuel trim cell values are less than -30 percent for 10 seconds.

Action Taken When the DTC Sets

DTCs P0171, P0172, P0174, P0175 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0171, P0172, P0174, P0175 are Type B DTCs.

Diagnostic Aids
    • The system will become lean if a fuel injector is not supplying enough fuel.
    • A lean condition could 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.
    • Review the Freeze Frame/Failure Records with a scan tool.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls Connector End 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

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls

Circuit/System Verification
  1. Verify that other DTCs are not set.
    2. ⇒If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .
  2. Ignition ON, observe the scan tool manifold absolute pressure (MAP) sensor pressure parameter.
  3. Compare the reading on the scan tool to the barometric pressure table. Refer to Altitude Versus Barometric Pressure .
    4. ⇒If not within the range specified for your altitude, refer to DTC P0107 or P0108 .
  4. Engine idling, observe the scan tool TP sensor percentage parameter. The reading should be less than 10 percent w/o throttle actuator control (TAC), and less than 17 percent with TAC.
    5. ⇒If greater than the applicable specified range, refer to DTC P0121, P0122, P0123, P0222, or P0223 w/o TAC or DTC P0121, P0122, P0123, P0221, P0222, or P0223 with TAC.
  5. Engine idling, observe the scan tool HO2S sensor voltage parameter. The reading should fluctuate within 200-800 mV.
    6. ⇒If not within the specified range, refer to DTC P0130 or P0150 .
  6. Engine at normal operating temperature, observe the scan tool Long Term FT parameter. The parameter should be between -5 to +5 percent.
  7. If the vehicle passes the Circuit/System Verification test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.

Circuit/System Testing
  1. Verify that none of the following conditions exist:

    2. P0171 or P0174

    • Splits, kinks, or improper connections at the vacuum hoses
    • Vacuum leaks at the intake manifold, throttle body, and injector O-rings
    • Leaking crankcase ventilation system
    • Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • The fuel system is operating lean. Refer to Fuel System Diagnosis .
    • The fuel injectors are operating lean. Refer to Fuel Injector Balance Test with Special Tool .
    • Missing, or leaking exhaust components.

    P0172 or P0175

    • Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • The fuel system is operating rich. Refer to Fuel System Diagnosis .
    • The fuel injectors are operating rich. Refer to Fuel Injector Balance Test with Special Tool .
    • The air intake duct for being collapsed or restricted possibly by a restricted air filter
    • Leaking fuel pressure regulator--Inspect for evidence of fuel in the vacuum line. Refer to Fuel System Diagnosis .
    • Excessive fuel in the crankcase.
    • The incorrect operation of the evaporative emissions control system.
    • Missing, or leaking exhaust components.
  2. 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.

    •  Fuel Injection Fuel Rail Assembly Replacement
    •  Air Cleaner Element Replacement