GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2008 🢒 Allure 🢒 Engine 🢒 Engine Controls and Fuel - 2.8L, 3.0L, 3.2L, or 3.6L 🢒 DTC P2177

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 P2177: Fuel Trim System Lean at Cruise or Accel

Circuit 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 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 HO2S inputs are added and used by the ECM to calculate short and long term fuel trim fuel delivery adjustments. If the HO2S indicate a lean condition, fuel trim values will be above 0 percent. If the oxygen sensor (O2S) indicate a rich condition, fuel trim values will be below 0 percent. Short term fuel trim values change rapidly in response to the HO2S signals. Long term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1.

Conditions for Running the DTC
    • Before the ECM can report DTC P2177 failed, DTCs P0030, P0031, P0032, P0053, P0101, P0121, P0122, P0123, P0130, P0131, P0132, P0133, P0135, P0221, P0222, P0223, P0335, P0336, P0338, P0443, P0458, P0459, P167A, P2096, P2097, P2195, P2196, P2231, P2237, P2243, P2251, and P2626 must run and pass.
    • DTCs P0010, P0011, P0013, P0014, P0020, P0021, P0023, P0024, P0455, P0496, P0117, P0118, P0125, P0201-P0206, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0276, P0277, P0300-P0306, P0461, P0462, P0463, P2088, P2089, P2090, P2091, P2092, P2093, P2094, P2095, and P2176 are not set.
    •  The fuel system is in closed loop.
    • The long fuel trim is active.
    • The engine coolant temperature (ECT) is greater than 60°C (140°F).
    • The intake air temperature (IAT) is less than 66°C (151°F).
    • The mass air flow is between 7-83 g/s.
    • The engine load is between 16-46 percent.
    • The evaporative emission (EVAP) canister purge solenoid valve is not enabled.
    • The fuel level is greater than 10 percent.
    • DTC P2177 runs continuously once the above conditions are met for at least 300 seconds.

Conditions for Setting the DTC
    • The Total Fuel Trim Average is greater than 23 percent.
    • The condition exists for 4 seconds, or for a cumulative of 50 seconds.

Action Taken when the DTC Sets

DTC P2177 is a Type B DTC.

Conditions for Clearing the MIL/DTC

DTC P2177 is a Type B DTC.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component 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

Control Module References for scan tool information

Diagnostic Aids
    • A fuel system delivery condition causes this DTC to set. Thoroughly inspect all items that cause a lean condition.
    • Any un-metered air into the engine causes this DTC to set. Thoroughly inspect all areas of the engine for vacuum leaks.

Circuit/System Verification
  1. Ignition ON, observe the scan tool DTC information. Verify there are no other DTCs set.
    2. ⇒If there are other DTCs set refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.
  2. Engine at normal operating temperature, observe the scan tool Total Fuel Trim Avg. parameter. The parameter should display between -22 to +23 percent.
    3. ⇒If not within the specified range, verify that none of the following conditions exist:
    • A mass air flow (MAF) sensor signal that is skewed--If the Short Term FT parameters for both banks changes greater than 20 percent when the MAF sensor is disconnected, refer to DTC P0101 for further diagnosis.
    • Inspect the HO2S 1 and HO2S 2 for being secure
    • Damaged wiring between either HO2S and the ECM
    • Inspect the throttle body and the intake manifold for vacuum leaks
    • Inspect for exhaust leaks, missing or loose exhaust hardware.
    • Inspect the crankcase ventilation system for leaks
    • Lean fuel injectors--Refer to Fuel Injector Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2
    • Incorrect fuel system pressure--Refer to Fuel System Diagnosis
    • Fuel that is contaminated--Refer to Alcohol/Contaminants-in-Fuel Diagnosis
    • Contaminated HO2S-Silicon
    • Inspect for a high engine oil level condition. A high engine oil level causes oil residue to form on the MAF sensor, causing a lean indication. The MAF sensor does not need to be replaced
  3. 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 are captured in the Freeze Frame/Failure Records Data List.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.